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Impulsive Acceleration of Coronal Mass Ejections. II. Relation to Soft X-Ray Flares and Filament Eruptions
Abstract
Using high time cadence images from the STEREO EUVI, COR1 and COR2
instruments, we derived detailed kinematics of the main acceleration stage for
a sample of 95 CMEs in comparison with associated flares and filament
eruptions. We found that CMEs associated with flares reveal on average
significantly higher peak accelerations and lower acceleration phase durations,
initiation heights and heights, at which they reach their peak velocities and
peak accelerations. This means that CMEs that are associated with flares are
characterized by higher and more impulsive accelerations and originate from
lower in the corona where the magnetic field is stronger. For CMEs that are
associated with filament eruptions we found only for the CME peak acceleration
significantly lower values than for events which were not associated with
filament eruptions. The flare rise time was found to be positively correlated
with the CME acceleration duration, and negatively correlated with the CME peak
acceleration. For the majority of the events the CME acceleration starts before
the flare onset (for 75% of the events) and the CME accleration ends after the
SXR peak time (for 77% of the events). In ~60% of the events, the time
difference between the peak time of the flare SXR flux derivative and the peak
time of the CME acceleration is smaller than \pm5 min, which hints at a
feedback relationship between the CME acceleration and the energy release in
the associated flare due to magnetic reconnection.
... CMEs reach their peak velocity at varying heights from the Sun. In general, fast CMEs reach their peak velocity at a low height, thanks to strong and impulsive acceleration, while slow CMEs reach their peak velocity at a relatively high height Bein et al. 2011Bein et al. , 2012Wood et al. 2017). Based on a statistical study of 95 events, Bein et al. (2011) found that the heights of peak velocity distribute from a very low height of 1.17 Rs (from disk center) to~10.5 Rs (close to the border height of STEREO COR2 used in this study). ...
... Based on a statistical study of 95 events, Bein et al. (2011) found that the heights of peak velocity distribute from a very low height of 1.17 Rs (from disk center) to~10.5 Rs (close to the border height of STEREO COR2 used in this study). A continued study by Bein et al. (2012) found that CMEs associated with flares, in comparison with CMEs associated with filaments, have on average significantly higher peak acceleration and lower height of peak velocities. Wood et al. (2017) found that the average peak velocity height was~3.2 ...
... Low coronal observations also revealed the close relationship between solar flares and CMEs (Schmieder et al. 2015;Vršnak 2016). Strong and powerful flares tend to be associated with fast and massive CMEs (Moon et al. 2002;Burkepile et al. 2004;Vršnak et al. 2005;Bein et al. 2012), which results in a 90% correspondence for flares above X-class (Yashiro et al. 2006). However, there exist flares without CMEs (i.e., confined flares (e.g., Pallavicini et al. 1977;Wang and Zhang 2007;Sun et al. 2015) and vice versa, CMEs without flares (e.g., stealth CMEs) (Robbrecht et al. 2009b;Ma et al. 2010;Howard and Harrison 2013;D'Huys et al. 2014). ...
This review article summarizes the advancement in the studies of Earth-affecting solar transients in the last decade that encompasses most of solar cycle 24. It is a part of the effort of the International Study of Earth-affecting Solar Transients (ISEST) project, sponsored by the SCOSTEP/VarSITI program (2014–2018). The Sun-Earth is an integrated physical system in which the space environment of the Earth sustains continuous influence from mass, magnetic field, and radiation energy output of the Sun in varying timescales from minutes to millennium. This article addresses short timescale events, from minutes to days that directly cause transient disturbances in the Earth’s space environment and generate intense adverse effects on advanced technological systems of human society. Such transient events largely fall into the following four types: (1) solar flares, (2) coronal mass ejections (CMEs) including their interplanetary counterparts ICMEs, (3) solar energetic particle (SEP) events, and (4) stream interaction regions (SIRs) including corotating interaction regions (CIRs). In the last decade, the unprecedented multi-viewpoint observations of the Sun from space, enabled by STEREO Ahead/Behind spacecraft in combination with a suite of observatories along the Sun-Earth lines, have provided much more accurate and global measurements of the size, speed, propagation direction, and morphology of CMEs in both 3D and over a large volume in the heliosphere. Many CMEs, fast ones, in particular, can be clearly characterized as a two-front (shock front plus ejecta front) and three-part (bright ejecta front, dark cavity, and bright core) structure. Drag-based kinematic models of CMEs are developed to interpret CME propagation in the heliosphere and are applied to predict their arrival times at 1 AU in an efficient manner. Several advanced MHD models have been developed to simulate realistic CME events from the initiation on the Sun until their arrival at 1 AU. Much progress has been made on detailed kinematic and dynamic behaviors of CMEs, including non-radial motion, rotation and deformation of CMEs, CME-CME interaction, and stealth CMEs and problematic ICMEs. The knowledge about SEPs has also been significantly improved. An outlook of how to address critical issues related to Earth-affecting solar transients concludes this article.
... Based on a statistical study of 95 events, Bein et al. (2011) found that the heights of peak velocity distribute from a very low height of 1.17 Rs (from disk center) to ~10.5 Rs (close to the border height of STEREO COR2 used in this study). A continued study by Bein et al. (2012) found that CMEs associated with flares, in comparison with CMEs associated with filaments, have on average significantly higher peak acceleration and lower height of peak velocities. Wood et al. (2017) found that the average peak-velocityheight was ~3.2 Rs for fast CMEs that were associated with flares, ~13.9 Rs for intermediate velocity CME associated with erupting filaments, and ~29.4 Rs for slow CMEs that were not associated with any apparent surface source regions. ...
... Strong and powerful flares tend to be associated with fast and massive CMEs (Moon et al. 2002;Burkepile et al. 2004;B. Vršnak, Sudar, and Ruždjak 2005b;Bein et al. 2012), which results in a 90% correspondence for flares above X-class (Yashiro et al. 2006). However, there exist flares without CMEs (i.e. ...
... The main acceleration phase of the CME is correlated with the time evolution of the flare-related hard X-ray burst (M. Temmer et al. 2008;Gou et al. 2020) and a close relationship between their onset times was found in statistical studies (Maričić et al. 2007;Bein et al. 2012). Further evidence for a close flare/CME relationship is provided by the strong correlation between characteristic CME parameters, such as the velocity, the acceleration and its kinetic energy with the SXR peak flux, indicating the flare strength, or the integrated flux of the associated flare (Vršnak, Sudar, and Ruždjak 2005b;Maričić et al. 2007;Yashiro and Gopalswamy 2009). ...
This review article summarizes the advancement in the studies of Earth-affecting solar transients in the last decade that encompasses most of solar cycle 24. The Sun Earth is an integrated physical system in which the space environment of the Earth sustains continuous influence from mass, magnetic field and radiation energy output of the Sun in varying time scales from minutes to millennium. This article addresses short time scale events, from minutes to days that directly cause transient disturbances in the Earth space environment and generate intense adverse effects on advanced technological systems of human society. Such transient events largely fall into the following four types: (1) solar flares, (2) coronal mass ejections (CMEs) including their interplanetary counterparts ICMEs, (3) solar energetic particle (SEP) events, and (4) stream interaction regions (SIRs) including corotating interaction regions (CIRs). In the last decade, the unprecedented multi viewpoint observations of the Sun from space, enabled by STEREO Ahead/Behind spacecraft in combination with a suite of observatories along the Sun-Earth lines, have provided much more accurate and global measurements of the size, speed, propagation direction and morphology of CMEs in both 3-D and over a large volume in the heliosphere. Several advanced MHD models have been developed to simulate realistic CME events from the initiation on the Sun until their arrival at 1 AU. Much progress has been made on detailed kinematic and dynamic behaviors of CMEs, including non-radial motion, rotation and deformation of CMEs, CME-CME interaction, and stealth CMEs and problematic ICMEs. The knowledge about SEPs has also been significantly improved.
... To understand the initiation and early evolution of CMEs, the relationship between their kinematic evolution and the light curve of their associated flares has been studied extensively. The three CME evolution phases were found to correspond to, respectively, the pre-flare phase, rise phase, and decay phase of the associated flare in soft X-rays (SXRs; Neupert et al. 2001;Zhang et al. 2001Zhang et al. , 2004Cheng et al. 2010;Bein et al. 2012). This is further supported by a statistical study of a sample of 22 CMEs performed by Maričić et al. (2007). ...
... The best fits of the h(t) data yield a relatively precise timing of the kinematic evolution, which is then compared with the flare light curve for each event. This might either yield a discrimination between the ideal MHD and resistive eruption models, or provide information on how early and closely the feedback between flux rope instability and reconnection is established, thereby adding to the substantial existing knowledge, which has not yet established a definite picture (Zhang & Dere 2006;Maričić et al. 2007;Bein et al. 2012). Similarly, a relatively precise height of the onset of both the slow-rise and main-acceleration phases is obtained, which we utilize to determine whether one of these onsets is related to the threshold of the torus instability. ...
We investigate the initiation and early evolution of 12 solar eruptions, including six active-region hot channel and six quiescent filament eruptions, which were well observed by the Solar Dynamics Observatory, as well as by the Solar Terrestrial Relations Observatory for the latter. The sample includes one failed eruption and 11 coronal mass ejections, with velocities ranging from 493 to 2140 km s ⁻¹ . A detailed analysis of the eruption kinematics yields the following main results. (1) The early evolution of all events consists of a slow-rise phase followed by a main-acceleration phase, the height–time profiles of which differ markedly and can be best fit, respectively, by a linear and an exponential function. This indicates that different physical processes dominate in these phases, which is at variance with models that involve a single process. (2) The kinematic evolution of the eruptions tends to be synchronized with the flare light curve in both phases. The synchronization is often but not always close. A delayed onset of the impulsive flare phase is found in the majority of the filament eruptions (five out of six). This delay and its trend to be larger for slower eruptions favor ideal MHD instability models. (3) The average decay index at the onset heights of the main acceleration is close to the threshold of the torus instability for both groups of events (although, it is based on a tentative coronal field model for the hot channels), suggesting that this instability initiates and possibly drives the main acceleration.
... However, magnetic reconnection forms closed loops and energizes plasmas and particles therein, resulting in impulsively enhanced flare radiation. The observed coincidence between the evolution of the CME kinematics and that of the flare X-ray fluxes indicates that the CME eruption is related to the reconnection that produces solar flares (Zhang et al. 2001(Zhang et al. , 2004Temmer et al. 2008;Bein et al. 2012;Patsourakos et al. 2013), as predicted by CME initiation models (e.g.,Chen 2011). Apart from flare light curves, morphological evolution of flare emission in the lower atmosphere has also been used to infer the reconnection process in the corona and indirectly measure the rate of magnetic reconnection (Forbes & Priest 1984;Poletto & Kopp 1986). ...
... To complement the foregoing correlation analysis on the overall progress of the CME acceleration and flare reconnection, here we investigate the timings when CME acceleration or flare reconnection begins to rise (Kahler et al. 1988;Zhang et al. 2001;Temmer et al. 2008;Liu et al. 2014;Wang et al. 2019). We choose the start time of CME acceleration t _ a st or that of flare reconnection rate t _ r st to be the moment when CME acceleration (or reconnection rate) has increased to 10% of the peak Bein et al. 2012). For this analysis, the time profile of the reconnection rate is smoothed with a boxcar of 5 minutes, similar to the time cadence of the CME observation. ...
Theoretically, coronal mass ejection (CME) kinematics are related to magnetic reconnection processes in the solar corona. However, the current quantitative understanding of this relationship is based on the analysis of only a handful of events. Here we report a statistical study of 60 CME-flare events from 2010 August to 2013 December. We investigate kinematic properties of CMEs and magnetic reconnection in the low corona during the early phase of the eruptions, by combining limb observations from STEREO with simultaneous on-disk views from SDO. For a subset of 42 events with reconnection rate evaluated by the magnetic fluxes swept by the flare ribbons on the solar disk observed from SDO, we find a strong correlation between the peak CME acceleration and the peak reconnection rate. Also, the maximum velocities of relatively fast CMEs (>600 km s −1) are positively correlated with the reconnection flux, but no such correlation is found for slow CMEs. A time-lagged correlation analysis suggests that the distribution of the time lag of CME acceleration relative to reconnection rate exhibits three peaks, approximately 10 minutes apart, and on average, acceleration-led events have smaller reconnection rates. We further compare the CME total mechanical energy with the estimated energy in the current sheet. The comparison suggests that, for small-flare events, reconnection in the current sheet alone is insufficient to fuel CMEs. Results from this study suggest that flare reconnection may dominate the acceleration of fast CMEs, but for events of slow CMEs and weak reconnection, other mechanisms may be more important.
... To understand the initiation and early evolution of CMEs, the relationship between their kinematic evolution and the light curve of their associated flares has been studied extensively. The three CME evolution phases were found to correspond to, respectively, the pre-flare phase, rise phase, and decay phase of the associated flare in soft X-rays (SXRs) (Zhang et al. 2001(Zhang et al. , 2004Neupert et al. 2001;Cheng et al. 2010;Bein et al. 2012). This is further supported by a statistical study of a sample of 22 CMEs performed by Maričić et al. (2007). ...
... The best fits of the h(t) data yield a relatively precise timing of the kinematic evolution, which is then compared with the flare light curve for each event. This might either yield a discrimination between the ideal MHD and resistive eruption models, or provide information on how early and closely the feedback between flux rope instability and reconnection is established, thereby adding to the substantial existing knowledge, which has not yet established a definite picture (Zhang & Dere 2006;Maričić et al. 2007;Bein et al. 2012). Similarly, a relatively precise height of the onset of both the slow-rise and main-acceleration phases is obtained, which we utilize to determine whether one of these onsets is related to the threshold of the torus instability. ...
We investigate the initiation and early evolution of 12 solar eruptions, including six active region hot channel and six quiescent filament eruptions, which were well observed by the \textsl{Solar Dynamics Observatory}, as well as by the \textsl{Solar TErrestrial RElations Observatory} for the latter. The sample includes one failed eruption and 11 coronal mass ejections, with velocities ranging from 493 to 2140~km~s$^{-1}$. A detailed analysis of the eruption kinematics yields the following main results. (1) The early evolution of all events consists of a slow-rise phase followed by a main-acceleration phase, the height-time profiles of which differ markedly and can be best fit, respectively, by a linear and an exponential function. This indicates that different physical processes dominate in these phases, which is at variance with models that involve a single process. (2) The kinematic evolution of the eruptions tends to be synchronized with the flare light curve in both phases. The synchronization is often but not always close. A delayed onset of the impulsive flare phase is found in the majority of the filament eruptions (5 out of 6). This delay, and its trend to be larger for slower eruptions, favor ideal MHD instability models. (3) The average decay index at the onset heights of the main acceleration is close to the threshold of the torus instability for both groups of events (although based on a tentative coronal field model for the hot channels), suggesting that this instability initiates and possibly drives the main acceleration.
... However, magnetic reconnection forms closed loops and energizes plasmas and particles therein, resulting in impulsively enhanced flare radiation. The observed coincidence between the evolution of the CME kinematics and that of the flare X-ray fluxes indicates that the CME eruption is related with the reconnection which produces solar flares (Zhang et al. 2001(Zhang et al. , 2004Temmer et al. 2008;Bein et al. 2012;Patsourakos et al. 2013), as predicted by CME initiation models (e.g., Chen 2011). Apart from flare light curves, morphological evolution of flare emission in the lower atmosphere has also been used to infer the reconnection process in the corona and indirectly measure the rate of magnetic reconnection (Forbes & Priest 1984;Poletto & Kopp 1986). ...
... To complement the foregoing correlation analysis on the overall progress of the CME acceleration and flare reconnection, here we investigate the timings when CME acceleration or flare reconnection begins to rise (Kahler et al. 1988;Zhang et al. 2001;Temmer et al. 2008;Liu et al. 2014;Wang et al. 2019). We choose the start time of CME acceleration t a st or that of flare reconnection rate t r st to be the moment when CME acceleration (or reconnection rate) has increased to 10% of the peak Bein et al. 2012). For this analysis, the time profile of the reconnection rate is smoothed with a boxcar of 5 min, similar to the time cadence of the CME observation. ...
Theoretically, CME kinematics are related to magnetic reconnection processes in the solar corona. However, the current quantitative understanding of this relationship is based on the analysis of only a handful of events. Here we report a statistical study of 60 CME-flare events from August 2010 to December 2013. We investigate kinematic properties of CMEs and magnetic reconnection in the low corona during the early phase of the eruptions, by combining limb observations from STEREO with simultaneous on-disk views from SDO. For a subset of 42 events with reconnection rate evaluated by the magnetic fluxes swept by the flare ribbons on the solar disk observed from SDO, we find a strong correlation between the peak CME acceleration and the peak reconnection rate. Also, the maximum velocities of relatively fast CMEs (> 600 km/s) are positively correlated with the reconnection flux, but no such correlation is found for slow CMEs. A time-lagged correlation analysis suggests that the distribution of the time lag of CME acceleration relative to reconnection rate exhibits three peaks, approximately 10 minutes apart, and on average, acceleration-lead events have smaller reconnection rates. We further compare the CME total mechanical energy with the estimated energy in the current sheet. The comparison suggests that, for small-flare events, reconnection in the current sheet alone is insufficient to fuel CMEs. Results from this study suggest that flare reconnection may dominate the acceleration of fast CMEs, but for events of slow CMEs and weak reconnection, other mechanisms may be more important.
... 0.41) for both GLEs and non-GLEs. This is similar to the values reported previously by several researchers (e.g., Moon et al. 2002;Vršnak et al. 2005;Yashiro & Gopalswamy 2009;Bein et al. 2012). The correlation strength between the flare peak and CME speed is more often weak, likely because the CME main acceleration pronounces over the flare rise phase and ceases over/around the flare peak (see Figure 1; see also, e.g., Qiu et al. 2004;Zhang et al. 2004;Li & Zank 2005). ...
... The standard flare-CME model (e.g., Aschwanden 2001Aschwanden , 2004Qiu et al. 2004;Forbes et al. 2006;Aschwanden et al. 2015;Grechnev et al. 2018) illustrates that the thermal/ nonthermal and mechanical energy are generally released from the same magnetic reconnection; the released thermal/nonthermal energy manifested in flare components and the mechanical energy manifested in CMEs are thus interrelated (e.g., Hundhausen 1993;Dryer 1994;Cliver et al. 2004;Yihua 2005;Aschwanden 2006Aschwanden , 2017Miklenic et al. 2009;Liu et al. 2010;Su et al. 2011Su et al. , 2013Bein et al. 2012;Grechnev et al. 2013Grechnev et al. , 2015a. Following the model, we observed (e.g., Figure 1) that the CME acceleration phase and SXR (thermal) flare rise phase evolve almost simultaneously. ...
Association of solar flares and coronal mass ejections (CMEs) with ground level enhancement (GLE) is a recognized fact, but the question arises when observed similar association with some non-GLEs. In this respect, we carry out a detailed study on the relation between flare fluences (ϕ J m-2) and CME speeds (Vcme km s-1) during some selected GLEs and non-GLEs. As found, most of the data points of ϕ (J m-2) and Vcme (km s-1) of GLEs follow a near-linear trend, with the ϕ (J m-2) increasing as the Vcme (km s-1) increase, resulting in a strong positive correlation (r ≥ 0.82), while the correlation (r≤0.47) remains weak for non-GLEs. For any exceptional GLE, the ϕ (J m-2) and Vcme (km s-1) that do not maintain a near-linear trend over flare whole phase do maintain at least a minimum rational proportionality over the flare rise phase, whereas this characteristic was not generally observed for non-GLEs. Although the ϕ (J m-2) and Vcme (km s-1) of some non-GLEs show the trend similar to those of GLEs, they indeed originated over the flare impulsive phases concomitant with coronal shock manifested in m-type II burst whilst GLEs originated over flare initial phase before the m-type II. Flare peak fluences (ϕpk J m-2) and Vcme (km s-1) maintain weak correlation for both GLEs and non-GLEs, likely because the CME main acceleration ceases around the flare peak. However, though the ϕpk (J m-2) governs the flare total fluence, it does not blur the correlation between the fluence over flare rise phase (ϕr J m-2) and Vcme (km s-1), indicating that the flare-peak/strength does not control the GLE occurrence.
... A very close coupling would favor our first three cases. However, Bein et al. (2012) found that the CME acceleration onset precedes the onset of the SXR flare emission in about 75 percent of all events with an average difference of 4-5 minutes. The differences obtained from our scalings stay in this range (Bein et al., 2012). ...
... However, Bein et al. (2012) found that the CME acceleration onset precedes the onset of the SXR flare emission in about 75 percent of all events with an average difference of 4-5 minutes. The differences obtained from our scalings stay in this range (Bein et al., 2012). Table 3.2. ...
The Sun is the nearest star to the Earth. It consists of an interior and an atmosphere. The convection zone is the outermost layer of the solar interior. A flux rope may emerge as a coherent structure from the convection zone into the solar atmosphere or be formed by magnetic reconnection in the atmosphere. A flux rope is a bundle of magnetic field lines twisting around an axis field line, creating a helical shape by which dense filament material can be supported against gravity. The flux rope is also considered as the key structure of the most energetic phenomena in the solar system, such as coronal mass ejections (CMEs) and flares. These magnetic flux ropes can produce severe geomagnetic storms. In particular, to improve the ability to forecast space weather, it is important to enrich our knowledge about the dynamic formation of flux ropes and the underlying physical mechanisms that initiate their eruption, such as a CME. A confined eruption consists of a filament eruption and usually an associated are, but does not evolve into a CME; rather, the moving plasma is halted in the solar corona and usually seen to fall back. The first detailed observations of a confined filament eruption were obtained on 2002 May 27by the TRACE satellite in the 195 A band. So, in the Chapter 3, we focus on a flux rope instability model. A twisted flux rope can become unstable by entering the kink instability regime. We show that the kink instability, which occurs if the twist of a flux rope exceeds a critical value, is capable of initiating of an eruption. This model is tested against the well observed confined eruption on 2002 May 27 in a parametric magnetohydrodynamic (MHD) simulation study that comprises all phases of the event. Very good agreement with the essential observed properties is obtained, only except for a relatively poor matching of the initial filament height. Therefore, in Chapter 4, we submerge the center point of the flux rope deeper below the photosphere to obtain a flatter coronal rope section and a better matching with the initial height profile of the erupting filament. This implies a more realistic inclusion of the photospheric line tying. All basic assumptions and the other parameter settings are kept the same as in Chapter 3. This complement of the parametric study shows that the flux rope instability model can yield an even better match with the observational data. We also focus in Chapters 3 and 4 on the magnetic reconnection during the confined eruption, demonstrating that it occurs in two distinct locations and phases that correspond to the observed brightenings and changes of topology, and consider the fate of the erupting flux, which can reform a (less twisted) flux rope. The Sun also produces series of homologous eruptions, i.e. eruptions which occur repetitively in the same active region and are of similar morphology. Therefore, in Chapter 5, we employ the reformed flux rope as a new initial condition, to investigate the possibility of subsequent homologous eruptions. Free magnetic energy is built up by imposing motions in the bottom boundary, such as converging motions, leading to flux cancellation. We apply converging motions in the sunspot area, such that a small part of the flux from the sunspots with different polarities is transported toward the polarity inversion line (PIL) and cancels with each other. The reconnection associated with the cancellation process forms more helical magnetic flux around the reformed flux rope, which leads to a second and a third eruption. In this study, we obtain the first MHD simulation results of a homologous sequence of eruptions that show a transition from a confined to two ejective eruptions, based on the reformation of a flux rope after each eruption.
... For instance, by transferring restraining overlying flux into flux of the erupting sheared core or flux rope, or by producing highly bent field lines in a rope that accelerates it by means of a slingshot effect (e.g., Linton et al. 2001;Mackay and van Ballegooijen 2006;Archontis and Török 2008). These two processes (instability and reconnection) often occur simultaneously and are closely coupled (e.g., Bein et al. 2012;Vršnak 2016, see also Sect. 2.2.3). ...
... Indeed, in eruptions of active-region structures, where the Alfvén speed is high and the source region is rather compact, the acceleration is usually much larger than in eruptions from quiet-sun regions (e.g. eruptions of quiescent prominences, stealth CMEs; see, e.g., Vršnak et al. 2005;Bein et al. 2012;Howard and Harrison 2013). Note that the relation a ≈ v 2 A /2d implies that in the case of very compact sources, d < 100 Mm, accelerations can achieve values on the order of 10 km s −2 , such as is observed in the most impulsive events Bein et al. 2011). ...
Coronal mass ejections (CMEs) were discovered in the early 1970s when space-borne coronagraphs revealed that eruptions of plasma are ejected from the Sun. Today, it is known that the Sun produces eruptive flares, filament eruptions, coronal mass ejections and failed eruptions; all thought to be due to a release of energy stored in the coronal magnetic field during its drastic reconfiguration. This review discusses the observations and physical mechanisms behind this eruptive activity, with a view to making an assessment of the current capability of forecasting these events for space weather risk and impact mitigation. Whilst a wealth of observations exist, and detailed models have been developed, there still exists a need to draw these approaches together. In particular more realistic models are encouraged in order to asses the full range of complexity of the solar atmosphere and the criteria for which an eruption is formed. From the observational side, a more detailed understanding of the role of photospheric flows and reconnection is needed in order to identify the evolutionary path that ultimately means a magnetic structure will erupt.
... Some analytical considerations have suggested that magnetic reconnection dominates in the impulsive acceleration phase (e.g., Vršnak 2016). This is supported by the synchronization between the CME velocity and SXR flux (Zhang et al. 2001(Zhang et al. , 2004Cheng et al. 2010;Bein et al. 2012), as well as between the acceleration of CMEs and HXR flux or reconnection rate (Qiu et al. 2004;Temmer et al. 2008Temmer et al. , 2010. In our study, the velocity and acceleration of the filament do not coincide with the flare SXR and HXR fluxes at all, respectively, which strongly supports that reconnection plays a negligible role in the acceleration. ...
The eruption of magnetic flux ropes (MFRs), often taking filaments together, leads to coronal mass ejections (CMEs). Theoretical studies propose that both the resistive magnetic reconnection and the ideal instability of an MFR system can release magnetic-free energy and accelerate CMEs (i.e., MFRs or filaments) during eruptions. Observations find that the full kinematic evolution of CMEs usually undergoes three phases: the initiation phase, impulsive acceleration phase, and propagation phase. The impulsive acceleration phase often starts and ceases simultaneously with the flare onset time and peak time, respectively. This synchronization can be explained by the positive feedback relationship between the acceleration of CMEs and flare magnetic reconnection, and suggests that the reconnection has the dominant contribution to the acceleration of CMEs. It is rare to see strong evidence that supports the dominant contribution of ideal instability to the acceleration. In this paper, we report an intriguing filament eruption that occurred on 2011 May 11. Its complete acceleration is well recorded by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. The kinematic analysis shows that the impulsive acceleration phase starts and ceases obviously earlier than the flare onset time and peak time, respectively, which means a complete asynchronization between the impulsive acceleration phase and flare rise phase, and strongly supports that the ideal instability plays a dominant role in this impulsive acceleration. Furthermore, the accompanied flare is a B-class one, also implying that the contribution of reconnection is negligible in the energy release process.
... Berkebile-Stoiser et al. (2012) similarly find that the onset of nonthermal HXR flare emission lags the CME acceleration onset for a majority of studied events (average lag ∼6 minutes), consistent with the standard CSHKP model for solar eruptive events; a slow rise in the flux rope is first observed, which leads to formation of a current sheet and the onset of reconnection and flare energy release. Other studies using SXR emission (e.g., Maričić et al. 2007;Bein et al. 2012) also observe that the flare onset follows the start of the CME acceleration for a majority of events. ...
We study the evolution of solar eruptive events by investigating the temporal relationships among magnetic reconnection, flare energy release, and the acceleration of coronal mass ejections (CMEs). Leveraging the optimal viewing geometry of the Solar TErrestrial RElations Observatory (STEREO) relative to the Solar Dynamics Observatory (SDO) and the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) during 2010–2013, we identify 12 events with sufficient spatial and temporal coverage for a detailed examination. STEREO and SDO data are used to measure the CME kinematics and the reconnection rate, respectively, and hard X-ray (HXR) measurements from RHESSI provide a signature of the flare energy release. This analysis expands upon previous solar eruptive event timing studies by examining the fast-varying features, or “bursts,” in the HXR and reconnection rate profiles, which represent episodes of energy release. Through a time lag correlation analysis, we find that HXR bursts occur throughout the main CME acceleration phase for most events, with the HXR bursts lagging the acceleration by 2 ± 9 minutes for fast CMEs. Additionally, we identify a nearly one-to-one correspondence between bursts in the HXR and reconnection rate profiles, with HXRs lagging the reconnection rate by 1.4 ± 2.8 minutes. The studied events fall into two categories: events with a single dominant HXR burst and events with a train of multiple HXR bursts. Events with multiple HXR bursts, indicative of intermittent reconnection and/or particle acceleration, are found to correspond with faster CMEs.
... The solar corona can accelerate CMEs through a variety of magnetic-based mechanisms, but they tend to decay suddenly with distance or time (Chen & Garren 1993;Chen & Krall 2003;Vršnak et al. 2004;Chen et al. 2006;Schrijver & Siscoe 2013). Hence, beyond a few solar radii, the effects (acceleration) of those mechanisms that set the initial speed of CMEs become negligible, leaving the interaction with the ambient solar wind as the dominant dynamic agent acting on the trajectories of CMEs (Zhang & Dere 2006;Bein et al. 2011Bein et al. , 2012. Although an approximation, it is physically reasonable that the average acceleration of CMEs can be related to the proper speed of CMEs and the ambient solar wind's expansion speed (Gopalswamy et al. 2000(Gopalswamy et al. , 2001. ...
Coronal mass ejections (CMEs) are one of the most relevant phenomena for space weather. Moreover, CMEs can negatively affect essential services and facilities. Therefore, to protect society, we require well-grounded knowledge of the physics that governs the propagation of CMEs from near the Sun to the orbit of Earth. In this work, we deduce expressions to approximate the main forces that affect the dynamic coupling between CMEs and the surrounding solar wind. Therefore, we explore the CME-solar wind dynamic coupling from a magnetohydrodynamic perspective, which, combined with a few reasonable assumptions, allows us to obtain expressions for the thermal and magnetic pressure forces, viscous and dynamic drag, and gravity. We simultaneously use our expressions to compute the trajectories of 34 Earth-directed CMEs. Our results, which are compared with in situ data, show significant quantitative consistency; our synthetic transits closely mimic their in situ observed counterparts. We conclude from our results that magnetic, thermal, and dynamic drag significantly surpass the other forces such as dynamic agents of CMEs in the interplanetary medium. In addition, we find that the initial relative speed of CMEs and solar wind is a determinant factor for the dynamic behavior of CMEs. In other words, subsonic CMEs are initially mostly affected by magnetic and thermal pressure forces, whereas super-magnetosonic CMEs are initially governed by inertial drag.
... Some recent observational work has compared the development of CMEs with that of the associated X-ray profiles. In a statistical comparison of 95 CMEs and associated X-ray flares Bein et al. (2012) found flare rise times positively correlated with CME acceleration durations, but for most events those acceleration phases ended after the X-ray peak times. Bak-Steślicka et al. (2013) found in addition that 24 GOES flares of long-duration (27-217 minutes) rise phase were associated with CMEs of high speed Vcme during the propagation phase, suggesting prolonged acceleration in those phases. ...
Recent work has shown that plots of solar flare X-ray peak temperatures, Tm, versus log peak fluxes, Fp, show statistically significant separations of lower Tm flares with fast (Vcme ≥ 1000 km s ⁻¹ ) and wide (Wcme = 360°) strong coronal mass ejections (CMEs) from higher Tm flares with no CMEs or slow (Vcme < 1000 km s ⁻¹ ) or narrow (<360°) weak CMEs. We extend that statistical separation to CME kinetic energies, Ecme. Flares with long-duration timescales also have well-known associations with fast CMEs and solar energetic ( E > 10 MeV) particle events. Using a data set of 585 ≥ M3.0 GOES X-ray flares, we ask whether longer flare timescales (rise times, TR; durations from onset to half-power decay, TD; decay times to half power, Td; and decay times to C2, TC2) also statistically discriminate among the three groups of CMEs for speeds, widths, and energies. All log–log plots of flare timescales versus Fp produce significant separations of the three groups of CMEs generally better than those of Tm versus log Fp. We use separations of CME distribution medians to sort the four flare timescales as effective discriminants among the three CME groups. Separations between the confined flares (no-CMEs) and weak CMEs are generally smaller than those between the weak CMEs and strong CMEs. A combination of Tm and TC2 provides optimum group separations, but Tm and log TD or log Td appears best for CME forecasting purposes.
... b Observational results for the December 22, 2009 CME event revealing the early evolution from combined EUV and coronagraph data (STEREO-B spacecraft) and GOES SXR flux profile for the related flare and derivative (proxy for HXR emission). Images reproduced with permission a from Temmer (2016), copyright by Wiley-VCH; and b from Bein et al. (2012), copyright by AAS The flare-CME feedback loop can be well explained by the CSHKP standard model (Carmichael 1964;Sturrock 1966;Hirayama 1974;Kopp and Pneuman 1976) through the magnetic reconnection process underlying both activity phenomena. In a simplistic scenario, we may summarize that magnetic reconnection drives particle acceleration (neglecting details on the actual acceleration process) leading to flare emission and closes magnetic field increasing the magnetic pressure inside the presumable CME flux rope (neglecting details on the actual magnetic configuration of the active region and surrounding). ...
The Sun, as an active star, is the driver of energetic phenomena that structure interplanetary space and affect planetary atmospheres. The effects of Space Weather on Earth and the solar system is of increasing importance as human spaceflight is preparing for lunar and Mars missions. This review is focusing on the solar perspective of the Space Weather relevant phenomena, coronal mass ejections (CMEs), flares, solar energetic particles (SEPs), and solar wind stream interaction regions (SIR). With the advent of the STEREO mission (launched in 2006), literally, new perspectives were provided that enabled for the first time to study coronal structures and the evolution of activity phenomena in three dimensions. New imaging capabilities, covering the entire Sun-Earth distance range, allowed to seamlessly connect CMEs and their interplanetary counterparts measured in-situ (so called ICMEs). This vastly increased our knowledge and understanding of the dynamics of interplanetary space due to solar activity and fostered the development of Space Weather forecasting models. Moreover, we are facing challenging times gathering new data from two extraordinary missions, NASA’s Parker Solar Probe (launched in 2018) and ESA’s Solar Orbiter (launched in 2020), that will in the near future provide more detailed insight into the solar wind evolution and image CMEs from view points never approached before. The current review builds upon the Living Reviews article by Schwenn from 2006, updating on the Space Weather relevant CME-flare-SEP phenomena from the solar perspective, as observed from multiple viewpoints and their concomitant solar surface signatures.
... Many models 49,50,51 predict that CME acceleration occurs primarily below 2 R☉. Only a handful of observations 52,53,55 have captured complete CME trajectories that track their acceleration through this region, or the associated impulsive expansion of the CME as it rises 54 . Likewise, models of reconnection in eruptions predict the formation of current sheets that drive flows and heating in the middle corona, but these have been observed only infrequently 23,56,57,58 and often the reconnection site itself lies outside the FOV of low coronal imagers 59 . ...
The "middle corona" is a critical transition between the highly disparate physical regimes of the lower and outer solar corona. Nonetheless, it remains poorly understood due to the difficulty of observing this faint region (1.5-3 solar radii). New observations from the GOES Solar Ultraviolet Imager in August and September 2018 provide the first comprehensive look at this region's characteristics and long-term evolution in extreme ultraviolet (EUV). Our analysis shows that the dominant emission mechanism here is resonant scattering rather than collisional excitation, consistent with recent model predictions. Our observations highlight that solar wind structures in the heliosphere originate from complex dynamics manifesting in the middle corona that do not occur at lower heights. These data emphasize that low-coronal phenomena can be strongly influenced by inflows from above, not only by photospheric motion, a factor largely overlooked in current models of coronal evolution. This study reveals the full kinematic profile of the initiation of several coronal mass ejections, filling a crucial observational gap that has hindered understanding of the origins of solar eruptions. These new data uniquely demonstrate how EUV observations of the middle corona provide strong new constraints on models seeking to unify the corona and heliosphere.
... Trottet et al., 2015). It is well known that the acceleration of CMEs is closely related in time with the evolution of thermal energy release in the associated flare suggesting a relationship between the CME speed and the peak flux or fluence of the SXR burst (Bein et al., 2012). Adding to this, Cane, Richardson, and Von Rosenvinge (2010) argued that the SXR flare fluence can serve as a proxy of the CME linear speed, especially for long duration events. ...
A consistent approach for the inherently imbalanced problem of Solar
Energetic Particle (SEP) events binary prediction is being presented. This is based on solar flare, coronal mass ejections (CMEs) data and combinations of both thereof.We exploit several machine learning (ML) and conventional statistics techniques to predict SEPs. The methods used are: logistic regression (LR), support vector machines (SVM), neural networks (NN) in the fully connected multi-layer perceptron (MLP) implementation, random forests (RF), decision
trees (DTs), extremely randomized trees (XT) and extreme gradient boosting (XGB). We provide an assessment of the methods employed and conclude that RF could be the prediction technique of choice for an optimal sample comprised by both flares and CMEs. The best-performing method gives a Probability of Detection (POD) of 0.76(�0.06), False Alarm Rate (FAR) of 0.34(�0.10), true skill statistic (TSS) 0.75(�0.05), and Heidke skill score (HSS) 0.69(�0.04). We further show that the most important features for the identification of SEPs, in
our sample, are the CME speed, width and flare soft X-ray (SXR) fluence.
Keywords: Solar Energetic Particles; Nowcasting; Machine Learning Methods; Forecasting
... Solar type II radio bursts are radio emissions characterized by a small speed of the frequency drift across the dynamic spectrum (McLean and Labrum, 1985). These radio bursts were first burst is localized in a small region of the shock front (Bemporad and Mancuso, 2011;Bein et al., 2012;Carley et al., 2013;Zimovets and Sadykov, 2015;Su et al., 2016) Bemporad and Mancuso (2011) concluded that the type II radio burst generated at the nose of the shock front, because the shock velocity here is usually larger than at the flanks. Reiner et al. (2003) found that type II radio bursts can be generated in a high-density coronal streamer when the shock flank travels through it. ...
The 13 June 2010 event was chosen as an example to find spots on a CME-related shock where type II radio bursts were generated. We used the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatory (SDO) data to find the shock and calculate the emission measure distribution over the solar limb in order to obtain various plasma characteristics ahead of and behind the shock front. A region was found in the shock where the electron density jump \(X\) on the shock front, the Alfvén Mach number \(M_{a}\) and the shock velocity \(V_{sh}\) reach a maximum simultaneously. Moreover, the calculated value of \(X\) in this region was found to be closest to the value of \(X^{rb}\) based on type II radio burst data, \((X^{rb})=N_{2}/N_{1}=(f_{u}/f_{l})^{2}\), where \(N_{2}\) and \(N_{1}\) are the electron densities at the upstream and downstream shock regions, \(f_{u}\) and \(f_{l}\) are the radio emission frequencies at the upper and lower band of the dynamic spectrum, in the second harmonic region. Based on these findings, we hypothesized that it is this shock region that is the source of type II radio bursts (type II RB). This region moves at an angle of \(+20^{\circ }\) from the center of the circle approximating the shock, relative to the direction through the shock middle. The type II radio burst source velocity is shown to be close to the CME-related shock velocity. This can be regarded as indirect evidence of the shocks being the source of type II radio bursts. A dependence, \(N_{1}(R_{sh})\), has been obtained in the \(+20^{\circ }\) direction, where \(R_{sh}\) is the shock front location. This dependence is shown to differ noticeably from the coronal background electron densities obtained by Newkirk (Astrophys. J. 133, 983, 1961) and Saito et al. (Ann. Tokyo Astron. Obs. 12, 53, 1970) density models.
... Zhang et al. (2001) investigated the relationship between CMEs and flares and proposed three kinematic evolution phases of CMEs: the slow rise phase, the impulsive acceleration phase, and the propagation phase, which are closely related to the pre-flare phase, the main phase, and the decay phase of associated flares, respectively. Such a synchronization has also been found in studies with more advanced observations, such as Maričić et al. (2007), Bein et al. (2012), and Cheng et al. (2020). Moreover, Temmer et al. (2008Temmer et al. ( , 2010 and Qiu et al. (2004) revealed a close correlation between the CME acceleration and the hard X-ray flux of flares. ...
In this Letter, we study the kinematic properties of ascending hot blobs associated with confined flares. Taking advantage of high-cadence extreme-ultraviolet images provided by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we find that for the 26 events selected here, the hot blobs are first impulsively accelerated outward, but then quickly slow down to motionlessness. Their velocity evolution is basically synchronous with the temporal variation of the Geostationary Operational Environmental Satellite soft X-ray flux of the associated flares, except that the velocity peak precedes the soft X-ray peak by minutes. Moreover, the duration of the acceleration phase of the erupting blobs is moderately correlated with that of the flare rise phase. For nine of the 26 cases, the erupting blobs even appear minutes prior to the onset of the associated flares. Our results show that a fraction of confined flares also involve the eruption of a magnetic flux rope, which sometimes is formed and heated prior to the flare onset. We suggest that the initiation and development of these confined flares are similar to that of eruptive ones, and the main difference may lie in the background field constraint, which is stronger for the former than for the latter.
... However, if an X-type HFT exists at the underside of an unstable MFR, then the HFT collapses into a vertical CS, and reconnection commences, simultaneously with the onset of the rise, i.e., flare and CME commence simultaneously. However, since flare onset and CME onset are rather well synchronized in the majority of eruptions (Zhang and Dere, 2006;Temmer et al, 2010;Cheng et al, 2020), with a trend though that CME rise starts before the impulsive flare energy release (in terms of the flare SXR and HXR emission, respectively) as shown in Bein et al (2012); Berkebile-Stoiser et al (2012), the time difference between them can only rarely be used to discriminate between SMA and MFR as the pre-eruptive structure. ...
A clear understanding of the nature of the pre-eruptive magnetic field configurations of Coronal Mass Ejections (CMEs) is required for understanding and eventually predicting solar eruptions. Only two, but seemingly disparate, magnetic configurations are considered viable; namely, sheared magnetic arcades (SMA) and magnetic flux ropes (MFR). They can form via three physical mechanisms (flux emergence, flux cancellation, helicity condensation). Whether the CME culprit is an SMA or an MFR, however, has been strongly debated for thirty years. We formed an International Space Science Institute (ISSI) team to address and resolve this issue and report the outcome here. We review the status of the field across modeling and observations, identify the open and closed issues, compile lists of SMA and MFR observables to be tested against observations and outline research activities to close the gaps in our current understanding. We propose that the combination of multi-viewpoint multi-thermal coronal observations and multi-height vector magnetic field measurements is the optimal approach for resolving the issue conclusively. We demonstrate the approach using MHD simulations and synthetic coronal images.
Our key conclusion is that the differentiation of pre-eruptive configurations in terms of SMAs and MFRs seems artificial. Both observations and modeling can be made consistent if the pre-eruptive configuration exists in a hybrid state that is continuously evolving from an SMA to an MFR. Thus, the ‘dominant’ nature of a given configuration will largely depend on its evolutionary stage (SMA-like early-on, MFR-like near the eruption).
... Zhang et al. (2001) investigated the relationship between CMEs and flares and proposed three kinematic evolution phases of CMEs: the slow rise phase, the impulsive acceleration phase, and the propagation phase, which are closely related to the pre-flare phase, the main phase, and the decay phase of associated flares, respectively. Such a synchronization has also been found in studies with more advanced observations, such as Maričić et al. (2007), Bein et al. (2012), and Cheng et al. (2020). Moreover, Temmer et al. (2008Temmer et al. ( , 2010 and Qiu et al. (2004) revealed a close correlation between the CME acceleration and the hard X-ray flux of flares. ...
In this Letter, we study the kinematic properties of ascending hot blobs associated with confined flares. Taking advantage of high-cadence extreme-ultraviolet images provided by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we find that for the 26 events selected here, the hot blobs are first impulsively accelerated outward, but then quickly slow down to motionlessness. Their velocity evolution is basically synchronous with the temporal variation of the Geostationary Operational Environmental Satellite soft X-ray flux of the associated flares, except that the velocity peak precedes the soft X-ray peak by minutes. Moreover, the duration of the acceleration phase of the erupting blobs is moderately correlated with that of the flare rise phase. For nine of the 26 cases, the erupting blobs even appear minutes prior to the onset of the associated flares. Our results show that a fraction of confined flares also involve the eruption of a magnetic flux rope, which sometimes is formed and heated prior to the flare onset. We suggest that the initiation and development of these confined flares are similar to that of eruptive ones, and the main difference may lie in the background field constraint, which is stronger for the former than for the latter.
... However, if an X-type HFT exists at the underside of an unstable MFR, then the HFT collapses into a vertical CS, and reconnection commences, simultaneously with the onset of the rise, i.e., flare and CME commence simultaneously. However, since flare onset and CME onset are rather well synchronized in the majority of eruptions (Zhang and Dere, 2006;Temmer et al, 2010;Cheng et al, 2020), with a trend though that CME rise starts before the impulsive flare energy release (in terms of the flare SXR and HXR emission, respectively) as shown in Bein et al (2012); Berkebile-Stoiser et al (2012), the time difference between them can only rarely be used to discriminate between SMA and MFR as the pre-eruptive structure. ...
A clear understanding of the nature of the pre-eruptive magnetic field configurations of Coronal Mass Ejections (CMEs) is required for understanding and eventually predicting solar eruptions. Only two, but seemingly disparate, magnetic configurations are considered viable; namely, sheared magnetic arcades (SMA) and magnetic flux ropes (MFR). They can form via three physical mechanisms (flux emergence, flux cancellation, helicity condensation) . Whether the CME culprit is an SMA or an MFR, however, has been strongly debated for thirty years. We formed an International Space Science Institute (ISSI) team to address and resolve this issue and report the outcome here. We review the status of the field across modeling and observations, identify the open and closed issues, compile lists of SMA and MFR observables to be tested against observations and outline research activities to close the gaps in our current understanding. We propose that the combination of multi-viewpoint multi-thermal coronal observations and multi-height vector magnetic field measurements is the optimal approach for resolving the issue conclusively. We demonstrate the approach using MHD simulations and synthetic coronal images. Our key conclusion is that the differentiation of pre-eruptive configurations in terms of SMAs and MFRs seems artificial. Both observations and modeling can be made consistent if the pre-eruptive configuration exists in a hybrid state that is continuously evolving from an SMA to an MFR. Thus, the 'dominant' nature of a given configuration will largely depend on its evolutionary stage (SMA-like early-on, MFR-like near the eruption).
... Such regions are expected above many ARs, as well as in QS regions (Evans et al., 2008;Zucca et al., 2014). High-resolution, multi-band EUV imaging, particularly from the SDO/AIA, has proven to be an excellent tool to study detailed morphology and kinematics of shocks, as well as key shock parameters including the compression ratio (Gopalswamy & Yashiro, 2011;Ma et al., 2011;Bein et al., 2012;Kozarev et al., 2015). Figure 4 shows an example of a coronal shock observed by AIA. ...
Accurate predictions of harmful space weather effects are mandatory for the protection of astronauts and other assets in space, whether in Earth or lunar orbit, in transit between solar system objects, or on the surface of other planetary bodies. Because the corona is multithermal (i.e., structured not only in space but also in temperature), wavelength-separated data provide crucial information that is not available to imaging methods that integrate over temperature. The extreme ultraviolet (EUV) wavelengths enable us to focus directly on high temperature coronal plasma associated with solar flares, coronal mass ejections (CMEs), and shocked material without being overwhelmed by intensity from the solar disk. Both wide-field imaging and spectroscopic observations of the solar corona taken from a variety of orbits (e.g., Earth, L1, or L5) using suitably-chosen EUV instrumentation offer the possibility of addressing two major goals to enhance our space weather prediction capability, namely: 1.) Improve our understanding of the coronal conditions that control the opening and closing of the corona to the heliosphere and consequent solar wind streams, and 2.) Improve our understanding of the physical processes that control the early evolution of CMEs and the formation of shocks, from the solar surface out into the extended corona.
... Geomagnetic storms driven by ICMEs may be predicted, based on the CME characteristics, between 2 and 4 days before arriving in the Earth environment. It is difficult nevertheless to get a better forecasting accuracy than 50% taking into account the different CME parameters (Bein et al., 2012;Gopalswamy et al., 2007;Jang et al., 2017;Vršnak et al., 2005). Moreover, interaction of ICMEs and interplanetary structures, for example, high-speed streams, is also reported to be drivers of severe geomagnetic activity (Gonzalez et al., 1996;Lugaz et al., 2017;Wang et al., 2003;Xie et al., 2006). ...
It is generally accepted that extreme space weather events tend to be related to strong flares and fast halo coronal mass ejections (CMEs). In the present paper, we carefully identify the chain of events from the Sun to the Earth induced by all 12 X‐class flares that occurred in 2002. In this small sample, we find an unusual high rate (58%) of solar sources with a longitude larger than 74°. Yet all 12 X‐class flares are associated with at least one CME. The fast halo CMEs (50%) are related to interplanetary CMEs (ICMEs) at L1 and weak Dst minimum values (more than −51 nT), while five (41%) of the 12 X‐class flares are related to solar proton events (SPEs).
We conclude that (i) all 12 analyzed solar events, even those associated with fast halo CMEs originating from the central disk region, and those ICMEs and SPEs were not very geo‐effective. This unexpected result demonstrates that the suggested events in the chain (fast halo CME, X‐class flares, central disk region, ICME, and SPE) are not infallible proxies for geo‐effectiveness. (ii) The low value of integrated and normalized southward component of the interplanetary magnetic field ( Bz*) may explain the low geo‐effectiveness for this small sample. In fact, Bz* is well correlated to the weak Dst and low auroral electrojet activity. Hence, the only space weather impact at Earth in 2002 we can explain is based on Bz* at L1.
... Geomagnetic storms driven by ICMEs may be predicted, based on the CME characteristics, between 2 and 4 days before arriving in the Earth environment. It is difficult nevertheless to get a better forecasting accuracy than 50% taking into account the different CME parameters (Bein et al., 2012;Gopalswamy et al., 2007;Jang et al., 2017;Vršnak et al., 2005). Moreover, interaction of ICMEs and interplanetary structures, for example, high-speed streams, is also reported to be drivers of severe geomagnetic activity (Gonzalez et al., 1996;Lugaz et al., 2017;Wang et al., 2003;Xie et al., 2006). ...
It is generally accepted that extreme space weather events tend to be related to strong flares and fast halo coronal mass ejections CMEs. In the present paper, we carefully identify the chain of events from the Sun to the Earth induced by all 12 X-class flares that occurred in 2002. In this small sample, we find an unusual high rate (58\%) of solar sources with a longitude larger than 74 degrees. Yet, all 12 X-class flares are associated with at least one CME. The fast halo CMEs (50\% ) are related to interplanetary CMEs (ICMEs) at L1 and weak Dst minimum values ($> -51\;$nT); while 5 (41\%) of the 12 X-class flares are related to solar proton events (SPE). We conclude that: (i) All twelve analyzed solar events, even those associated with fast halo CMEs originating from the central disk region, and those ICMEs and SPEs were not very geo-effective. This unexpected result demonstrates that the suggested events in the chain (fast halo CME, X-class flares, central disk region, ICME, SPE) are not infallible proxies for geo-effectiveness. (ii) The low value of integrated and normalized southward component of the IMF ($B^*_z$) may explain the low geo-effectiveness for this small sample. In fact, $B^*_z$ is well correlated to the weak Dst and low auroral electrojet (AE) activity. Hence, the only space weather impact at Earth in 2002 we can explain is based on $B^*_z$ at L1.
... Salas-Matamoros & Klein (2015), Moon et al. (2002), and Yashiro & Gopalswamy (2009) restricted their study to limb CMEs, for which the projection effects on the velocity is expected to be less important, and found a correlation of 0.48, 0.45, and 0.50 between the CME speed and SXR, respectively. Bein et al. (2012) and Vršnak et al. (2005) found correlation coefficients of 0.32 and 0.35 for unrestricted events. Moon et al. (2003) found a higher correlation coefficient of 0.93 with a carefully selected set of 8 events, for which they corrected the projection effects on the CME velocity. ...
We present the statistical analysis of 33 flare-related coronal jets, and discuss the link between the jet and the flare properties in these events. We selected jets that were observed between 2010 and 2016 by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory ( SDO ) that are temporally and spatially associated with flares observed by the Reuven Ramaty High Energy Solar Spectrometric Imager ( RHESSI ). For each jet, we calculated the jet duration and projected velocity in the plane of sky. The jet duration distribution has a median of 18.8 minutes. The projected velocities are between 31 and 456 km s ⁻¹ , with a median at 210 km s ⁻¹ . For each associated flare, we performed X-ray imaging and spectroscopy and identify nonthermal emission. Nonthermal emission was detected in only 1/4 of the events considered. We did not find a clear correlation between the flare thermal energy or soft X-ray (SXR) peak flux and the jet velocity or jet duration. There is no preferential time delay between the flare and the jet. The X-ray emission is generally located at the base of the jet. The analysis presented in this paper suggests that the flare and jet are part of the same explosive event, that the jet is driven by the propagation of an Alfvénic perturbation, and that the energy partition between flare and jets varies substantially from one event to another.
... Previously, Vrsnak et al. (2005) noticed that the CMEs associated with larger flares are generally faster and broader than those with small flares. A similar result is also found by Bein et al. (2012). Here we provide more detailed evidence. ...
Coronal mass ejections (CMEs) play a decisive role in driving space weather, especially the fast ones (e.g., with speeds above 800 km s ⁻¹ ). Understanding the trigger mechanisms of fast CMEs can help us gain important information in forecasting them. The filament eruptions accompanied with CMEs provide a good tracer in studying the early evolution of CMEs. Here we surveyed 66 filament-accompanied fast CMEs to analyze the correlation between the trigger mechanisms, namely either magnetic reconnection or ideal MHD process, associated flares, and CME speeds. Based on the data gathered from SDO , GONG, and STEREO , we find that (1) active region (AR) filament and intermediate filament (IF) eruptions show a higher probability for producing fast CMEs than quiet Sun (QS) filaments, while the probability of polar crown (PC) filament eruptions is zero in our statistic; (2) AR filament eruptions that produce fast CMEs are more likely to be triggered by magnetic reconnection, while QS filaments and IFs are more likely to be triggered by an ideal MHD process; (3) for AR filaments and IFs, it seems that the specific trigger mechanism does not have a significant influence on the resulting CME speeds, while for the QS filaments, the ideal MHD mechanism can more likely generate a faster CME; (4) comparing with previous statistical studies, the onset heights of filament eruptions and the decay indexes of the overlying field show some differences: for AR filaments and IFs, the decay indexes are larger and much closer to the theoretical threshold, while for QS filaments, the onset heights are higher than those obtained in previous results.
... This impulsive phase of acceleration is believed to be governed by the Lorentz self-force where the outward magnetic pressure dominates over the external and/or internal magnetic tension force (Byrne et al. 2010). Importantly, the peak acceleration height (1.67 ± 0.08 R S ) of the cavity obtained in this study is in agreement with the mean value (1.72 R S ) of that found for the filament associated CMEs studied by Bein et al. (2012). However, after 2 R S the average acceleration reduces to below 50 m/sec 2 which is believed to be the "residual acceleration phase" of the CME where the Lorentz self-force undergoes the declining phase and the flux-rope dynamics become strongly dependent on the drag force (Chen & Krall 2003). ...
We present the evolution of a coronal cavity encompassing its quiescent and eruptive phases in the lower corona. Using multiple vantage-point observations from the SDO /AIA, STEREO SECCHI/EUVI, and PROBA2 /Sun Watcher with the APS and Image Processing (SWAP) extreme ultraviolet (EUV) imagers, we capture a sequence of quasi-static equilibria of the quiescent cavity, which exhibited a slow rise and an expansion phase during its passage on the solar disk from 2010 May 30 to June 13. By comparing the decay-index profiles of the cavity system during the different stages of its quiescent and pre-eruptive phases, we find that the decay-index value at the cavity centroid height can be used as a good indicator to predict the cavity eruption in the context of torus instability. Combining the observations of SWAP and the Large Angle and Spectrometric Coronagraph Experiment C2/C3, we show the evolution of the EUV cavity into the white-light cavity as a three-part structure of the associated coronal mass ejection that was observed to erupt on 2010 June 13. By applying successive geometrical fits to the cavity morphology, we find that the cavity exhibited non-self-similar expansion in the lower corona, below 2.2 ± 0.2 R S , which points to the spatial scale for the radius of the source surface where the coronal magnetic field lines are believed to become radial. Furthermore, the kinematic study of the erupting cavity captures both the “impulsive” and “residual” phases of acceleration along with a strong deflection of the cavity at 1.3 R S . We also discuss the role of driving forces behind the dynamics of the morphological and kinematic evolution of the cavity.
... This impulsive phase of acceleration is believed to be governed by the Lorentz self-force where the outward magnetic pressure dominates over the external and/or internal magnetic tension force (Byrne et al. 2010). Importantly, the peak acceleration height (1.67 ± 0.08 R S ) of the cavity obtained in this study is in agreement with the mean value (1.72 R S ) of that found for the filament associated CMEs studied by Bein et al. (2012). However, after 2 R S the average acceleration reduces to below 50 m/sec 2 which is believed to be the "residual acceleration phase" of the CME where the Lorentz self-force undergoes the declining phase and the flux-rope dynamics become strongly dependent on the drag force (Chen & Krall 2003). ...
We present the evolution of a coronal cavity encompassing its quiescent and eruptive phases in the lower corona. Using the multi-vantage point observations from the SDO/AIA, STEREO SECCHI/EUVI and PROBA2/SWAP EUV imagers, we capture the sequence of quasi-static equilibria of the quiescent cavity which exhibited a slow rise and expansion phase during its passage on the solar disc from 2010 May 30 to 2010 June 13. By comparing the decay-index profiles of the cavity system during the different stages of its quiescent and pre-eruptive phases we find that the decay-index value at the cavity centroid height can be used as a good indicator to predict the cavity eruption in the context of torus instability. Combining the observations of SWAP and LASCO C2/C3 we show the evolution of the EUV cavity into the white-light cavity as a three-part structure of the associated CME observed to erupt on 2010 June 13. By applying successive geometrical fits to the cavity morphology we find that the cavity exhibited non self-similar expansion in the lower corona, below 2.2 +/- 0.2 Rs, which points to the spatial scale for the radius of source surface where the coronal magnetic field lines are believed to become radial. Furthermore, the kinematic study of the erupting cavity captures both the "impulsive" and "residual" phases of acceleration along with a strong deflection of the cavity at 1.3 Rs. We also discuss the role of driving forces behind the dynamics of the morphological and kinematic evolution of the cavity.
... Salas-Matamoros & Klein (2015); Moon et al. (2002); Yashiro & Gopalswamy (2009) restricted their study to limb CME, for which the projection effects on the velocity as expected to be less important, and found a correlation of 0.48, 0.45 and 0.50 between the CME speed and SXR respectively. Bein et al. (2012); Vršnak et al. (2005) found correlation coefficients of 0.32 and 0.35 for unrestricted events. Moon et al. (2003) found a higher correlation coefficient of 0.93 with a carefully selected set of 8 events for which they corrected the projection effects on the CME velocity. ...
We present the statistical analysis of 33 flare-related coronal jets, and discuss the link between the jet and the flare properties in these events. We selected jets that were observed between 2010 and 2016 by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO) and are temporally and spatially associated to flares observed by the Reuven Ramaty High Energy Solar Spectrometric Imager (RHESSI). For each jet, we calculated the jet duration and projected velocity in the plane of sky. The jet duration distribution has a median of 18.8 minutes. The projected velocities are between 31 km/s and 456 km/s with a median at 210 km/s. For each associated flare, we performed X-ray imaging and spectroscopy and identify non-thermal emission. Non-thermal emission was detected in only 1/4 of the event considered. We did not find a clear correlation between the flare thermal energy or SXR peak flux and the jet velocity. A moderate anti-correlation was found between the jet duration and the flare SXR peak flux. There is no preferential time delay between the flare and the jet. The X-ray emission is generally located at the base of the jet. The analysis presented in this paper suggests that the flare and jet are part of the same explosive event, that the jet is driven by the propagation of an Alfvenic perturbation, and that the energy partition between flare and jets varies substantially from one event to another.
... Although there seems to be a close relation between CMEs and solar flares, not all solar flares are accompanied by CMEs. Bein et al. (2012) reported that 25% of CMEs were not associated with solar flares. It is also known that solar flares without CMEs exist (Yashiro et al. 2006). ...
Statistical dependences among features of coronal mass ejections (CMEs), solar flares, and sigmoidal structures in soft-X-ray images were investigated. We applied analysis methods to all the features in the same way in order to investigate the reproducibility of the correlations among them, which may be found from previous statistical studies. Samples of 211 M-class and X-class flares, observed between 2006 and 2015 by the Hinode/X-ray telescope, Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph, and Geostationary Operational Environmental Satellite, were examined statistically. Five kinds of analysis were performed: occurrence rate analysis, linear-correlation analysis, association analysis, the Kolmogorov-Smirnov test, and the Anderson-Darling test. These give three main results. First, the sigmoidal structure and long-duration events (LDEs) have a stronger dependence on CME occurrence than large X-ray-class events in on-disk events. Second, for the limb events, a significant dependence exists between LDEs and CME occurrence, and between X-ray-class events and CME occurrence. Third, 32.4% of on-disk flare events have sigmoidal structure and are not accompanied by CMEs. However, the occurrence probability of CMEs without sigmoidal structure is very small, 8.8%, in on-disk events. While the first and second results are consistent with previous studies, we provide for the first time a difference between the on-disk and limb events. The third result, that non-sigmoidal regions produce fewer eruptive events, is also different from previous results. We suggest that sigmoidal structures in soft X-ray images will be a helpful feature for CME prediction in on-disk flare events. © 2018. The American Astronomical Society. All rights reserved.
... Thus, despite the important progress accomplished in recent years, in this article we have decided to develop an innovative approach by studying each Earth-directed event leading to an SSC in the magnetosphere during 2002 (maximum activity of Cycle 23). This unprecedented, comprehensive study consists in: i) starting from the list of SSCs, 1 ii) linking each SSC to a CME, iii) filling in the observational gaps along the Sun-Earth chain as much as possible, and iv) identifying one or many solar sources, with a clear signature on the Sun, in a temporal window determined by considering two extreme propagation velocities (300 and 1500 km s −1 ) (Bein et al., 2012). When there is no CME identified as the source of the observed SSC, we seek what process in the solar wind may have led to the SSC, with the help of observations at the Lagrangian point L1. ...
... Having three eyes viewing the Sun from different vantage points, many new insights about the initiation and subsequent propagation of coronal mass ejections (CMEs) in interplanetary space could be gained. Novel methods on 3D reconstructions of CMEs (Thernisien, Vourlidas, and Howard, 2009;Mierla et al., 2010), and with that, more detailed studies with respect to CME associated solar surface phenomena (e.g., flares or large-scale waves) were pursued, that could largely improve the understanding of CMEs (e.g., Kienreich, Temmer, and Veronig, 2009;Temmer et al., 2010;Bein et al., 2012). In situ measurements at 1 AU show signatures that can be related to CME-associated solar surface signatures as well as direct observations of CMEs in white-light. ...
... We analyze the rising motion of the eruptions, using data from EUVI (Extreme Ultraviolet Imager, Wuelser et al. 2004), COR1 and COR2 (Inner and Outer Coronagraphs, Thompson et al. 2003), that are all comprised in SECCHI (Sun Earth Connection Coronal and Heliospheric Investigation, Howard et al. 2008) on board STEREO-A. We further apply a CME detection tool (Bein et al. 2011(Bein et al. , 2012 to track the eruption structure in EUVI and COR1, COR2 images, by which its kinematics is obtained using a spline fit method. ...
In this paper, we analyzed a failed and a successful eruption that initiated from the same polarity inversion line within NOAA AR 11387 on December 25, 2011. They both started from a reconnection between sheared arcades, having distinct pre-eruption conditions and eruption details: before the failed one, the magnetic fields of the core region had a weaker non-potentiality; the external fields had a similar critical height for torus instability, a similar local torus-stable region, but a larger magnetic flux ratio (of low corona and near-surface region) as compared to the successful one. During the failed eruption, a smaller Lorentz force impulse was exerted on the outward ejecta; the ejecta had a much slower rising speed. Factors that might lead to the initiation of the failed eruption are identified: 1) a weaker non-potentiality of the core region, and a smaller Lorentz force impulse gave the ejecta a small momentum; 2) the large flux ratio, and the local torus-stable region in the corona provided strong confinements that made the erupting structure regain an equilibrium state.
... Thus, despite the important progress accomplished in recent years, in this article we have decided to develop an innovative approach by studying each Earth-directed event leading to an SSC in the magnetosphere during 2002 (maximum activity of Cycle 23). This unprecedented, comprehensive study consists in: i) starting from the list of SSCs, 1 ii) linking each SSC to a CME, iii) filling in the observational gaps along the Sun-Earth chain as much as possible, and iv) identifying one or many solar sources, with a clear signature on the Sun, in a temporal window determined by considering two extreme propagation velocities (300 and 1500 km s −1 ) (Bein et al., 2012). When there is no CME identified as the source of the observed SSC, we seek what process in the solar wind may have led to the SSC, with the help of observations at the Lagrangian point L1. ...
Taking the 32 storm sudden commencements (SSCs) listed by ISGI during 2002 as a starting point, we performed a multi-criterion analysis based on observations (propagation time, velocity comparisons, sense of the magnetic field rotation, radio waves) to associate them with solar sources. We identified their effects in the interplanetary medium, and looked at the response of the terrestrial ionized and neutral environment. We find that 28 SSCs can be related to 44 coronal mass ejections (CMEs), 15 with a unique CME and 13 with a series of multiple CMEs, among which 19 involved halo CMEs; 12 of the 19 fastest CMEs with speeds greater than 1000 km/s are halo CMEs. The probability for an SSC to occur is 75% if the CME is a halo CME. The complex interactions between two CMEs and the modification of their trajectories have been examined using joint white-light and multiple-wavelength radio observations. The solar-wind structures at L1 after the shocks leading the 32 SSCs are 12 magnetic clouds (MCs), 6 interplanetary CMEs (ICMEs) without an MC structure, 4 miscellaneous structures, which cannot unambiguously be classified as ICMEs, 5 corotating or stream interaction regions (CIRs/SIRs), and 4 isolated shock events; note than one CIR caused two SSCs. The 11 MCs listed in 3 or more MC catalogs covering the year 2002 are associated with SSCs. For the 3 most intense geomagnetic storms related to MCs, we note 2 sudden increases of the Dst, at the arrival of the sheath and the arrival of the MC itself. The most geoeffective events are MCs, since 92% of them trigger moderate or intense storms, followed by ICMEs (33%). At best, CIRs/SIRs only cause weak storms. We show that these geoeffective events (ICMEs or MCs) trigger or reinforce terrestrial radiowave activity in the magnetosphere, an enhanced convection in the ionosphere, and a stronger response in the thermosphere.
... We believe that the temporal correlation between the first acceleration phase and signatures of the flare reconnection is not a coincidence. For the majority of CMEs, the impulsive acceleration is correlated with the rise of the soft X-ray flux (Maričić et al. 2007;Bein et al. 2012), the hard X-ray bursts (Temmer et al. 2008(Temmer et al. , 2010, and peak of the reconnection rate (Qiu et al. 2004). ...
We study the coronal mass ejection (CME) with a complex acceleration profile. The event occurred on April 23, 2009. It had an impulsive acceleration phase, an impulsive deceleration phase, and a second impulsive acceleration phase. During its evolution, the CME showed signatures of different acceleration mechanisms: kink instability, prominence drainage, flare reconnection, and a CME-CME collision. The special feature of the observations is the usage of the TESIS EUV telescope. The instrument could image the solar corona in the Fe 171 \AA\ line up to a distance of 2 $R_\odot$ from the center of the Sun. This allows us to trace the CME up to the LASCO/C2 field of view without losing the CME from sight. The onset of the CME was caused by kink instability. The mass drainage occurred after the kink instability. The mass drainage played only an auxiliary role: it decreased the CME mass, which helped to accelerate the CME. The first impulsive acceleration phase was caused by the flare reconnection. We observed the two ribbon flare and an increase of the soft X-ray flux during the first impulsive acceleration phase. The impulsive deceleration and the second impulsive acceleration phases were caused by the CME-CME collision. The studied event shows that CMEs are complex phenomena that cannot be explained with only one acceleration mechanism. We should seek a combination of different mechanisms that accelerate CMEs at different stages of their evolution.
... Novel methods of 3D reconstructions of CMEs (Thernisien, Vourlidas, and Howard, 2009;Mierla et al., 2010) and with this, more detailed studies of CME-associated solar surface phenomena (e.g., flares or large-scale waves) were pursued, which were able to largely improve the understanding of CMEs (e.g. Kienreich, Temmer, and Veronig, 2009;Temmer et al., 2010;Bein et al., 2012). In situ measurements at 1 AU show signatures that can be related to CME-associated solar surface signatures, as well as direct observations of CMEs in white light. ...
We analyze the well observed flare-CME event from October 1, 2011 (SOL2011-10-01T09:18) covering the complete chain of action - from Sun to Earth - for a better understanding of the dynamic evolution of the CME and its embedded magnetic field. We study the solar surface and atmosphere associated with the flare-CME from SDO and ground-based instruments, and also track the CME signature off-limb from combined EUV and white-light data with STEREO. By applying 3D reconstruction techniques (GCS, total mass) to stereoscopic STEREO-SoHO coronagraph data, we track the temporal and spatial evolution of the CME in interplanetary space and derive its geometry and 3D-mass. We combine the GCS and Lundquist model results to derive the axial flux and helicity of the MC from in-situ measurements (Wind). This is compared to nonlinear force-free (NLFF) model results as well as to the reconnected magnetic flux derived from the flare ribbons (flare reconnection flux) and the magnetic flux encompassed by the associated dimming (dimming flux). We find that magnetic reconnection processes were already ongoing before the start of the impulsive flare phase, adding magnetic flux to the flux rope before its final eruption. The dimming flux increases by more than 25% after the end of the flare, indicating that magnetic flux is still added to the flux rope after eruption. Hence, the derived flare reconnection flux is most probably a lower limit for estimating the magnetic flux within the flux rope. We find that the magnetic helicity and axial magnetic flux are reduced in interplanetary space by ~50% and 75%, respectively, possibly indicating to an erosion process. A mass increase of 10% for the CME is observed over the distance range from ~4-20 Rs. The temporal evolution of the CME associated core dimming regions supports the scenario that fast outflows might supply additional mass to the rear part of the CME.
... These findings are consistent: the time integral of acceleration yields velocity, and the time integral of the rate of magnetic flux being swept by ribbons (∝ acceleration) yields the total magnetic flux swept by ribbons (∝ velocity). Bein et al. (2012) suggested a "feedback relationship" between CME acceleration and the rate of magnetic reconnection that, in principle, is directly related to the rate of flux being swept out by ribbons. In numerical simulations of a CME's formation and acceleration, Karpen, Antiochos, and DeVore (2012) also found that their model ejection's acceleration was closely tied to the onset of fast reconnection beneath the rising ejection. ...
Coronal mass ejections (CMEs) are the primary drivers of severe space weather disturbances in the heliosphere. Many CME models invoke ideal magnetohydrodynamics (MHD) to explain the onset and subsequent acceleration of ejections. Both observations and numerical modeling, however, suggest that magnetic reconnection likely plays a major role in most, if not all, fast CMEs. Here, we theoretically investigate the accretion of magnetic flux onto a rising ejection by reconnection involving the ejection's background field. This reconnection alters the magnetic structure of the ejection and its environment, thereby modifying the eruption's dynamics, generically leading to faster acceleration of the CME. Our analysis implies that CME models that neglect the effects of reconnection cannot accurately describe observed CME dynamics. Our ultimate aim is to characterize changes in CME acceleration in terms of observable properties of magnetic reconnection, such as the amount of reconnected flux, deduced from observations of flare ribbons and photospheric magnetic fields.
... Nevertheless, since these are only three events, they do not affect the statistical relationships and their late emission was not taken into account in the following analysis where we consider that the CME acceleration is most pronounced during the rise phase of the SXR burst (e.g. Maričić et al. 2007;Bein et al. 2012). We use the fluence at 3 GHz (/ 3 GHz ), 9 GHz (/ 9 GHz ) and the maximum fluence (/ max ) when it could be identified. ...
The propagation of a coronal mass ejection (CME) to the Earth takes between about 15 h and several days. We explore whether observations of non-thermal microwave bursts, produced by near-relativistic electons via the gyrosynchrotron process, can be used to predict travel times of interplanetary coronal mass ejections (ICMEs) from the Sun to the Earth. In a first step, a relationship is established between the CME speed measured by the Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph (SoHO/LASCO) near the solar limb and the fluence of the microwave burst. This relationship is then employed to estimate speeds in the corona of earthward-propagating CMEs. These speeds are fed into a simple empirical interplanetary acceleration model to predict the speed and arrival time of the ICMEs at Earth. The predictions are compared with observed arrival times and with the predictions based on other proxies, including soft X-rays (SXR) and coronographic measurements. We found that CME speeds estimated from microwaves and SXR predict the ICME arrival at the Earth with absolute errors of 11 ± 7 and 9 ± 7 h, respectively. A trend to underestimate the interplanetary travel times of ICMEs was noted for both techniques. This is consistent with the fact that in most cases of our test sample, ICMEs are detected on their flanks. Although this preliminary validation was carried out on a rather small sample of events (11), we conclude that microwave proxies can provide early estimates of ICME arrivals and ICME speeds in the interplanetary space. This method is limited by the fact that not all CMEs are accompanied by non-thermal microwave bursts. But its usefulness is enhanced by the relatively simple observational setup and the observation from ground, which makes the instrumentation less vulnerable to space weather hazards.
Aims. We perform a statistical study of the relations between the properties of solar energetic electron (SEE) events measured by the MESSENGER mission from 2010 to 2015 and the parameters of the respective parent solar activity phenomena in order to identify the potential correlations between them. During the time of analysis, the MESSENGER heliocentric distance varied between 0.31 and 0.47 au.
Methods. We used a published list of 61 SEE events measured by MESSENGER, which includes information on the near-relativistic electron peak intensities, the peak-intensity energy spectral indices, and the measured X-ray peak intensity of the flares related to the SEE events. Taking advantage of multi-viewpoint remote-sensing observations, we reconstructed, whenever possible, the associated coronal mass ejections (CMEs) and shock waves; and we determined the three-dimensional (3D) properties (location, speed, and width) of the CMEs and the maximum speed of the 3D CME-driven shocks in the corona. We used different methods (Spearman, Pearson, and a Bayesian approach, namely the Kelly method to linear regression) to estimate the correlation coefficients between the flare intensity, maximum speed at the apex of the CME-driven shock, CME speed at the apex, and CME width with the electron peak intensities and with the energy spectral indices. In this statistical study, we considered and addressed the limitations of the particle instrument on board MESSENGER (elevated background intensity level, anti-Sun pointing).
Results. There is an asymmetry to the east in the range of connection angles (CAs) for which the SEE events present the highest peak intensities, where the CA is the longitudinal separation between the footpoint of the magnetic field connecting to the spacecraft and the flare location. Based on this asymmetry, we define a subsample of well-connected events as when −65° ≤ CA ≤ +33°. For the well-connected sample, we find moderate to strong correlations between the near-relativistic electron peak intensity and the 3D CME-driven shock maximum speed at the apex (Spearman: cc = 0.53 ± 0.05; Pearson: cc = 0.65 ± 0.04; Kelly: cc = 0.87 ± 0.20), the flare peak intensity (Spearman: cc = 0.63 ± 0.03; Pearson: cc = 0.59 ± 0.03; Kelly: cc = 0.74 ± 0.30), and the 3D CME speed at the apex (Spearman: cc = 0.50 ± 0.04; Pearson: cc = 0.46 ± 0.03; Kelly: cc = 0.60 ± 0.39). When including poorly connected events (full sample), the relations between the peak intensities and the solar-activity phenomena are blurred, showing lower correlation coefficients.
Conclusions. Based on the comparison of the correlation coefficients presented in this study using near 0.4 au data, (1) both flare and shock-related processes may contribute to the acceleration of near relativistic electrons in large SEE events, in agreement with previous studies based on near 1 au data; and (2) the maximum speed of the CME-driven shock is a better parameter to investigate particle-acceleration-related mechanisms than the average CME speed, as suggested by the stronger correlation with the SEE peak intensities.
Context. Coronal and interplanetary shock waves produced by coronal mass ejections (CMEs) are major drivers of space-weather phenomena, inducing major changes in the heliospheric radiation environment and directly perturbing the near-Earth environment, including its magnetosphere. A better understanding of how these shock waves evolve from the corona to the interplanetary medium can therefore contribute to improving nowcasting and forecasting of space weather. Early warnings from these shock waves can come from radio measurements as well as coronagraphic observations that can be exploited to characterise the dynamical evolution of these structures.
Aims. Our aim is to analyse the geometrical and kinematic properties of 32 CME shock waves derived from multi-point white-light and ultraviolet imagery taken by the Solar Dynamics Observatory (SDO), Solar and Heliospheric Observatory (SoHO), and Solar-Terrestrial Relations Observatory (STEREO) to improve our understanding of how shock waves evolve in 3D during the eruption of a CME. We use our catalogue to search for relations between the shock wave’s kinematic properties and the flaring activity associated with the underlying genesis of the CME piston.
Methods. Past studies have shown that shock waves observed from multiple vantage points can be aptly reproduced geometrically by simple ellipsoids. The catalogue of reconstructed shock waves provides the time-dependent evolution of these ellipsoidal parameters. From these parameters, we deduced the lateral and radial expansion speeds of the shocks evolving over time. We compared these kinematic properties with those obtained from a single viewpoint by SoHO in order to evaluate projection effects. Finally, we examined the relationships between the shock wave and the associated flare when the latter was observed on the disc by considering the measurements of soft and hard X-rays.
Results. We find that at around 25 solar radii ( R ⊙ ), the shape of a shock wave is very spherical, with a ratio between the lateral and radial dimensions (minor radii) remaining at around b / a ≈ 1.03 and a radial to lateral speed ratio ( V R / V L )≈1.44. The CME starts to slow down a few tens of minutes after the first acceleration and then propagates at a nearly constant speed. We revisit past studies that show a relation between the CME speed and the soft X-ray emission of the flare measured by the Geostationary Operational Environmental Satellite (GOES) and extend them to higher flare intensities and shock speeds. The time lag between the peak of the flare and of the CME speed is up to a few tens of minutes. We find that for several well-observed shock onsets, a clear correlation is visible between the derivative of the soft X-ray flux and the acceleration of the shock wave.
The ‘middle corona’ is a critical transition between the highly disparate physical regimes of the lower and outer solar coronae. Nonetheless, it remains poorly understood due to the difficulty of observing this faint region (1.5–3 R☉). New observations from the Solar Ultraviolet Imager of a Geostationary Operational Environmental Satellite in August and September 2018 provide the first comprehensive look at this region’s characteristics and long-term evolution in extreme ultraviolet. Our analysis shows that the dominant emission mechanism here is resonant scattering rather than collisional excitation, consistent with recent model predictions. Our observations highlight that solar wind structures in the heliosphere originate from complex dynamics manifesting in the middle corona that do not occur at lower heights. These data emphasize that low-coronal phenomena can be strongly influenced by inflows from above, not only by photospheric motion, a factor largely overlooked in current models of coronal evolution. This study reveals the full kinematic profile of the initiation of several coronal mass ejections, filling a crucial observational gap that has hindered understanding of the origins of solar eruptions. These new data uniquely demonstrate how extreme ultraviolet observations of the middle corona provide strong new constraints on models seeking to unify the corona and heliosphere.
The focus is on the physical background and comprehension of the origin and the heliospheric propagation of interplanetary coronal mass ejections (ICMEs), which can cause most severe geomagnetic disturbances. The paper considers mainly the analytical modelling, providing useful insight into the nature of ICMEs, complementary to that provided by numerical MHD models. It is concentrated on physical processes related to the origin of CMEs at the Sun, their heliospheric propagation, up to the effects causing geomagnetic perturbations. Finally, several analytical and statistical forecasting tools for space weather applications are described.
Since Coronal Mass Ejections (CMEs) are the major drivers of space weather, it is crucial to study their evolution starting from the inner corona.
In this work we use Graduated Cylindrical Shell (GCS) model to study the 3D evolution of 59 CMEs in the inner ($<$ 3R$_{\odot}$) and outer ($>$ 3R$_{\odot}$) corona using observations from COR-1 and COR-2 on-board Solar TErrestrial RElations Observatory (STEREO) spacecraft. We identify the source regions of these CMEs and classify them as CMEs associated with Active Regions (ARs), Active Prominences (APs), and Prominence Eruptions (PEs). We find 27 $\%$ of CMEs show true expansion and 31 $\%$ show true deflections as they propagate outwards. Using 3D kinematic profiles of CMEs, we connect the evolution of true acceleration with the evolution of true width in the inner and outer corona. Thereby providing the observational evidence for the influence of the Lorentz force on the kinematics to lie in the height range of $2.5-3$ R$_{\odot}$. We find a broad range in the distribution of peak 3D speeds and accelerations ranging from 396 to 2465 km~s$^{-1}$ and 176 to 10922 m~s$^{-2}$ respectively with a long tail towards high values coming mainly from CMEs originating from ARs or APs. Further, we find the magnitude of true acceleration is be inversely correlated to its duration with a power law index of -1.19. We believe that these results will provide important inputs for the planning of upcoming space missions which will observe the inner corona and the models that study CME initiation and propagation.
As one of the payloads for the Advanced Space-based Solar Observatory (ASO-S) mission, the Lyman-alpha (Ly α ) Solar Telescope (LST) is aimed at imaging the Sun and the inner corona up to 2.5R ⊙ (mean solar radius) in both the Ly α (121.6 nm) and visible wavebands with high temporo-spatial resolution, mainly targeting solar flares, coronal mass ejections (CMEs) and filaments/prominences. LST observations allow us to trace solar eruptive phenomena from the disk center to the inner corona, to study the relationships between eruptive prominences/filaments, solar flares and CMEs, to explore the dynamical processes and evolution of solar eruptions, to diagnose solar winds, and to derive physical parameters of the solar atmosphere. LST is actually an instrument suite, which consists of a Solar Disk Imager (SDI), a Solar Corona Imager (SCI), aWhite-light Solar Telescope (WST) and two Guide Telescopes (GTs). This is the first paper in a series of LST-related papers. In this paper, we introduce the scientific objectives, present an overview of the LST payload and describe the planned observations. The detailed design and data along with potential diagnostics are described in the second (Paper II) and third (Paper III) papers, respectively, appearing in this issue.
Coronal mass ejections (CMEs) have been observed most commonly with white-light coronagraphs, which have a built-in occulting disk that eclipses the bright solar disk. This has the consequence that the lowest possible altitude of a CME detection is given by the diameter of the occulting disk.
We present a statistical study of 62 coronal dimming events associated with Earth-directed CMEs during the quasi-quadrature period of STEREO and SDO. This unique setting allows us to study both phenomena in great detail and compare characteristic quantities statistically. Coronal dimmings are observed on-disk by SDO/AIA and HMI, while the CME kinematics during the impulsive acceleration phase is studied close to the limb with STEREO/EUVI and COR, minimizing projection effects. The dimming area, its total unsigned magnetic flux and its total brightness, reflecting properties of the total dimming region at its final extent, show the highest correlations with the CME mass (c ∼ 0.6 − 0.7). Their corresponding time derivatives, describing the dynamics of the dimming evolution, show the strongest correlations with the CME peak velocity (c ∼ 0.6). The highest correlation of c = 0.68 ± 0.08 is found with the mean intensity of dimmings, indicating that the lower the CME starts in the corona, the faster it propagates. No significant correlation between dimming parameters and the CME acceleration was found. However, for events where high-cadence STEREO observations were available, the mean unsigned magnetic field density in the dimming regions tends to be positively correlated with the CME peak acceleration (c = 0.42 ± 0.20). This suggests that stronger magnetic fields result in higher Lorentz forces providing stronger driving force for the CME acceleration. Specific coronal dimming parameters correlate with both, CME and flare quantities providing further evidence for the flare-CME feedback relationship. For events in which the CME occurs together with a flare, coronal dimmings statistically reflect the properties of both phenomena.
We investigate on the relationship between flares and coronal mass ejections (CMEs) in which a flare started before and after the CME events which differ in their physical properties, indicating potentially different initiation mechanisms. The physical properties of two types flare-correlated CME remain an interesting and important question in space weather. We study the relationship between flares and CMEs using a different approach requiring both temporal and spatial constraints during the period from December 1, 2008 to April 30, 2017 in which the CMEs data were acquired by SOHO/LASCO (Solar and Heliospheric Observatory/Large Angle Spectrometric Coronagraph) over the solar cycle 24. The soft X-ray flare flux data, such as flare class, location, onset time and integrated flux, are collected from Geostationary Environmental satellite (GOES) and XRT Flare catalogs. We selected 307 CMEs-flares pairs applying simultaneously temporal and spatial constraints in all events for the distinguish between two associated CME-flare types. We study the correlated properties of coincident flares and CMEs during this period, specifically separating the sample into two types: flares that precede a CME and flares that follow a CME. We found an opposite correlation relationship between the acceleration and velocity of CMEs in the After- and Before-CMEs events. We found a log-log relation between the width and mass of CMEs in the two associated types. The CMEs and flares properties show that there were significant differences in all physical parameters such as (mass, angular width, kinetic energy, speed and acceleration) between two flare-associated CME types.
Coronal dimmings, localized regions of reduced emission in the EUV and soft X-rays, are interpreted as density depletions due to mass loss during the CME expansion. They contain crucial information on the early evolution of CMEs low in the corona. For 62 dimming events, characteristic parameters are derived, statistically analyzed and compared with basic flare quantities. On average, coronal dimmings have a size of 2.15×10^10 km^2 , contain a total unsigned magnetic flux of 1.75 ×10^21 Mx, and show a total brightness decrease of −1.91× 10^6 DN, which results in a relative decrease of ~60% compared to the pre-eruption intensity level. Their main evacuation phase lasts for ~50 minutes. The dimming area, the total dimming brightness, and the total unsigned magnetic flux show the highest correlation with the flare SXR fluence (c>0.7). Their corresponding time derivatives, describing the dimming dynamics, strongly correlate with the GOES flare class (c>0.6). For 60% of the events we identified core dimmings, i.e. signatures of an erupting flux rope. They contain 20% of the magnetic flux covering only 5% of the total dimming area. Secondary dimmings map overlying fields that are stretched during the eruption and closed down by magnetic reconnection, thus adding flux to the erupting flux rope via magnetic reconnection. This interpretation is supported by the strong correlation between the magnetic fluxes of secondary dimmings and flare reconnection fluxes (c = 0.63±0.08), the balance between positive and negative magnetic fluxes (c = 0.83±0.04) within the total dimmings and the fact that for strong flares (>M1.0) the reconnection and secondary dimming fluxes are roughly equal.
The structure and dynamics of the outer solar atmosphere are reviewed with emphasis on the role played by the magnetic field. Contemporary observations that focus on high resolution imaging over a range of temperatures, as well as UV, EUV and hard X-ray spectroscopy, demonstrate the presence of a vast range of temporal and spatial scales, mass motions, and particle energies present. By focusing on recent developments in the chromosphere, corona and solar wind, it is shown that small scale processes, in particular magnetic reconnection, play a central role in determining the large-scale structure and properties of all regions. This coupling of scales is central to understanding the atmosphere, yet poses formidable challenges for theoretical models.
Using an observed relation between speeds of CMEs near the Sun and in the solar wind, we determine an “effective” acceleration acting on the CMEs. We found a linear relation between this effective acceleration and the initial speed of the CMEs. The acceleration is similar to that of the slow solar wind in magnitude. The average solar wind speed naturally divides CMEs into fast and slow ones. Based on the relation between the acceleration and initial speed, we derive an empirical model to predict the arrival of CMEs at 1 AU.
The Solar and Heliospheric Observatory (SOHO) mission's white light
coronagraphs have observed nearly 7000 coronal mass ejections (CMEs)
between 1996 and 2002. We have documented the measured properties of all
these CMEs in an online catalog. We describe this catalog and present a
summary of the statistical properties of the CMEs. The primary
measurements made on each CME are the apparent central position angle,
the angular width in the sky plane, and the height (heliocentric
distance) as a function of time. The height-time measurements are then
fitted to first- and second-order polynomials to derive the average
apparent speed and acceleration of the CMEs. The statistical properties
of CMEs are (1) the average width of normal CMEs (20° < width
≤ 120°) increased from 47° (1996; solar minimum) to 61°
(1999; early phase of solar maximum) and then decreased to 53°
(2002; late phase of solar maximum), (2) CMEs were detected around the
equatorial region during solar minimum, while during solar maximum CMEs
appear at all latitudes, (3) the average apparent speed of CMEs
increases from 300 km s-1 (solar minimum) to 500 km
s-1 (solar maximum), (4) the average apparent speed of halo
CMEs (957 km s-1) is twice of that of normal CMEs (428 km
s-1), and (5) most of the slow CMEs (V ≤ 250 km
s-1) show acceleration while most of the fast CMEs (V >
900 km s-1) show deceleration. Solar cycle variation and
statistical properties of CMEs are revealed with greater clarity in this
study as compared with previous studies. Implications of our findings
for CME models are discussed.
We report on the statistical relationships between solar flares and coronal mass ejections (CMEs) observed during 1996-2007 inclusively. We used soft X-ray flares observed by the Geostationary Operational Environmental Satellite (GOES) and CMEs observed by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO) mission. Main results are (1) the CME association rate increases with flare's peak flux, fluence, and duration, (2) the difference between flare and CME onsets shows a Gaussian distribution with the standard deviation σ = 17 min (σ = 15 min) for the first (second) order extrapolated CME onset, (3) the most frequent flare site is under the center of the CME span, not near one leg (outer edge) of the CMEs, (4) a good correlation was found between the flare fluence versus the CME kinetic energy. Implications for flare-CME models are discussed.
We use high time cadence images acquired by the STEREO EUVI and COR instruments to study the evolution of coronal mass ejections (CMEs) from their initiation through impulsive acceleration to the propagation phase. For a set of 95 CMEs we derived detailed height, velocity, and acceleration profiles and statistically analyzed characteristic CME parameters: peak acceleration, peak velocity, acceleration duration, initiation height, height at peak velocity, height at peak acceleration, and size of the CME source region. The CME peak accelerations we derived range from 20 to 6800 m s-2 and are inversely correlated with the acceleration duration and the height at peak acceleration. Seventy-four percent of the events reach their peak acceleration at heights below 0.5 R sun. CMEs that originate from compact sources low in the corona are more impulsive and reach higher peak accelerations at smaller heights. These findings can be explained by the Lorentz force, which drives the CME accelerations and decreases with height and CME size.
We studied the distribution of plane-of-sky speeds determined for 4315 coronal mass ejections (CMEs) detected by the Large Angle and Spectrometric Coronagraph Experiment on board the Solar and Heliospheric Observatory (SOHO LASCO). We found that the speed distributions for accelerating and decelerating events are nearly identical and to a good approximation they can be fitted with a single lognormal distribution. This finding implies that, statistically, there is no physical distinction between the accelerating and the decelerating events. The lognormal distribution of the CME speeds suggests that the same driving mechanism of a nonlinear nature is acting in both slow and fast dynamical types of CMEs.
The temporal relationship between coronal mass ejections (CMEs) and associated solar flares is of great importance to understanding the origin of CMEs, but it has been difficult to study owing to the nature of CME detection. In this paper, we investigate this issue using the Large Angle and Spectrometric Coronagraph and the EUV Imaging Telescope observations combined with GOES soft X-ray observations. We present four well-observed events whose source regions are close to the limb such that we are able to directly measure the CMEs' initial evolution in the low corona (~ 1-3 R☉) without any extrapolation; this height range was not available in previous space-based coronagraph observations. The velocity-time profiles show that kinematic evolution of three of the four CMEs can be described in a three-phase scenario: the initiation phase, impulsive acceleration phase, and propagation phase. The initiation phase is characterized by a slow ascension with a speed less than 80 km s-1 for a period of tens of minutes. The initiation phase always occurs before the onset of the associated flare. Following the initiation phase, the CMEs display an impulsive acceleration phase that coincides very well with the flares' rise phase lasting for a few to tens of minutes. The acceleration of CMEs ceases near the peak time of the soft X-ray flares. The CMEs then undergo a propagation phase, which is characterized by a constant speed or slowly decreasing in speed. The acceleration rates in the impulsive acceleration phase are in the range of 100-500 m s-2. One CME (on 1997 November 6, associated with an X9.4 flare) does not show an initiation phase. It has an extremely large acceleration rate of 7300 m s-2. The possible causes of CME initiation and acceleration in connection with flares are explored.
We report the kinematic properties of a set of three coronal mass ejections (CMEs) observed with the LASCO (Large Angle and Spectrometric Coronagraph) on the Solar and Heliospheric Observatory (SOHO) spacecraft, which showed characteristics of impulsive, intermediate, and gradual acceleration, respectively. The first CME had a 30 minute long fast acceleration phase during which the average acceleration was about 308 m s-2; this acceleration took place over a distance of about 3.3 R☉ (from 1.3 to 4.6 R☉, height measured from disk center). The CME characterized by intermediate acceleration had a long acceleration phase of about 160 minutes during which the average acceleration was about 131 m s-2; the CME traveled a distance of at least 4.3 R☉, reaching a height of 7.0 R☉ at the end of the acceleration phase. The CME characterized by gradual acceleration had no fast acceleration phase. Instead, it displayed a persistent weak acceleration lasting more than 24 hr with an average acceleration of only 4.0 m s-2 throughout the LASCO field of view (from 1.1 to 30 R☉). This study demonstrates that the final velocity of a CME is determined by a combination of acceleration magnitude and acceleration duration, both of which can vary significantly from event to event. The first two CME events were associated with soft X-ray flares. We found that in the acceleration phase there was close temporal correlation both between the CME velocity and the soft X-ray flux of the flare and between the CME acceleration and derivative of the X-ray flux. These correlations indicate that the CME large-scale acceleration and the flare particle acceleration are strongly coupled physical phenomena occurring in the corona.
A high-velocity coronal mass ejection (CME) associated with the 2002 April 21 X1.5 flare is studied using a unique set of observations from the Transition Region and Coronal Explorer (TRACE), the Ultraviolet Coronagraph Spectrometer (UVCS), and the Large Angle and Spectroscopic Coronagraph (LASCO). The event is first observed as a rapid rise in GOES X-rays, followed by two simultaneous brightenings that appear to be connected by an ascending looplike feature. While expanding, the appearance of the feature remains remarkably constant as it passes through the TRACE 195 Å passband and LASCO fields of view, allowing its height-time behavior to be accurately determined. The acceleration is consistent with an exponential rise with an e-folding time of ~138 s and peaks at ~1500 m s-2 when the leading edge is at ~1.7 R☉ from Sun center. The acceleration subsequently falls off with an e-folding time of over 1000 s. At distances beyond ~3.4 R☉, the height-time profile is approximately linear with a constant velocity of ~2500 km s-1. These results are briefly discussed in light of recent kinematic models of CMEs.
We study two well-observed, fast halo CMEs, covering the full CME kinematics including the initiation and impulsive acceleration phase, and their associated flares. We find a close synchronization between the CME acceleration profile and the flare energy release as indicated by the RHESSI hard X-ray flux onsets, as well as peaks occur simultaneously within 5 minutes. These findings indicate a close physical connection between both phenomena and are interpreted in terms of a feedback relationship between the CME dynamics and the reconnection process in the current sheet beneath the CME.
A comprehensive statistical study is performed to address the question of whether two classes of coronal mass ejections (CMEs) exist. A total of 3217 CME events observed by SOHO/LASCO in 1996–2000 have been analyzed. We have examined the distributions of CMEs according to speed and acceleration, respec-tively, and investigated the correlation between speed and acceleration of CMEs. This statistical analysis is conducted for two subsets containing those CMEs that show a temporal and spatial association either with GOES X-ray solar flares or with eruptive filaments. We have found that CMEs associated with flares have a higher median speed than those associated with eruptive filaments and that the median speed of CMEs associated with strong flares is higher than that of weak-flare–associated CMEs. The distribution of CME acceleration shows a conspicuous peak near zero, not only for the whole data set, but also for the two subsets associated either with solar flares or with eruptive filaments. However, we have confirmed that the CMEs associated with major flares tend to be more decelerated than the CMEs related to eruptive filaments. The fraction of flare-associated CMEs has a tendency to increase with the CME speed, whereas the fraction of eruptive-filament–associated CMEs tends to decrease with the CME speed. This result supports the concept of two CME classes. We have found a possibility of two components in the CME speed distribution for both the CME data associated with flares larger than M1 class and the CME data related with limb flares. Our results suggest that the apparent single-peak distribution of CME speed can be attributed to the projection effect and possibly to abundance of small flares too. We also note that there is a possible correlation between the speed of CMEs and the time-integrated X-ray flux of the CME-associated limb flares.
Using the potential of two unprecedented missions, Solar Terrestrial Relations Observatory (STEREO) and Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI), we study three well-observed fast coronal mass ejections (CMEs) that occurred close to the limb together with their associated high-energy flare emissions in terms of RHESSI hard X-ray (HXR) spectra and flux evolution. From STEREO/EUVI and STEREO/COR1 data, the full CME kinematics of the impulsive acceleration phase up to ~4 R <SUB>sun</SUB> is measured with a high time cadence of <=2.5 minutes. For deriving CME velocity and acceleration, we apply and test a new algorithm based on regularization methods. The CME maximum acceleration is achieved at heights h <= 0.4 R <SUB>sun</SUB>, and the peak velocity at h <= 2.1 R <SUB>sun</SUB> (in one case, as small as 0.5 R <SUB>sun</SUB>). We find that the CME acceleration profile and the flare energy release as evidenced in the RHESSI HXR flux evolve in a synchronized manner. These results support the "standard" flare/CME model which is characterized by a feedback relationship between the large-scale CME acceleration process and the energy release in the associated flare.
The main challenge for the theory of solar eruptions has been to understand two basic aspects of large flares. These are the cause of the flare itself and the nature of the morphological features which form during its evolution. Such features include separating ribbons of H\(\alpha\) emission joined by a rising arcade of soft x-ray loops, with hard x-ray emission at their summits and at their feet. Two major advances in our understanding of the theory of solar flares have recently occurred. The first is the realisation that a magnetohydrodynamic (MHD) catastrophe is probably responsible for the basic eruption and the second is that the eruption is likely to drive a reconnection process in the field lines stretched out by the eruption. The reconnection is responsible for the ribbons and the set of rising soft x-ray loops, and such a process is well supported by numerical experiments and detailed observations from the Japanese satellite Yohkoh.
Magnetic energy conversion by reconnection in two dimensions is relatively well understood, but in three dimensions we are only starting to understand the complexity of the magnetic topology and the MHD dynamics which are involved. How the dynamics lead to particle acceleration is even less well understood. Particle acceleration in flares may in principle occur in a variety of ways, such as stochastic acceleration by MHD turbulence, acceleration by direct electric fields at the reconnection site, or diffusive shock acceleration at the different kinds of MHD shock waves that are produced during the flare. However, which of these processes is most important for producing the energetic particles that strike the solar surface remains a mystery.
Based on our previous works regarding solar eruptions, we focus on the relationships among different eruptive phenomena, such
as solar flares, eruptive prominences and coronal mass ejections (CMEs). The three processes show clear correlations under
certain circumstances. The correlation between a CME and solar flare depends the energy that stored in the relevant magnetic
structure, which is available to drive the eruption: the more energy that is stored, the better the correlation is; otherwise,
the correlation is poor. The correlation between a CME and eruptive prominence, on the other hand, depends on the plasma mass
concentration in the configuration prior to the eruption: if the mass concentration is significant, a CME starts with an eruptive
prominence, otherwise, a CME develops an without an apparent associated eruptive prominence. These results confirm that solar
flares, eruptive prominences and CMEs are different significances of a single physical process that is related to the energy
release in a disrupted coronal magnetic field. The impact of gravity on CME propagation and the above correlations is also
investigated. Our calculations indicate that the effect of gravity is not significant unless the strength of the background
field in the disrupted magnetic configuration becomes weak, say weaker than 30G.
Coronal mass ejections (CMEs) are routinely identified in the images of the solar corona obtained by the Solar and Heliospheric
Observatory (SOHO) mission’s Large Angle and Spectrometric Coronagraph (LASCO) since 1996. The identified CMEs are measured
and their basic attributes are cataloged in a data base known as the SOHO/LASCO CME Catalog. The Catalog also contains digital
data, movies, and plots for each CME, so detailed scientific investigations can be performed on CMEs and the related phenomena
such as flares, radio bursts, solar energetic particle events, and geomagnetic storms. This paper provides a brief description
of the Catalog and summarizes the statistical properties of CMEs obtained using the Catalog. Data products relevant to space
weather research and some CME issues that can be addressed using the Catalog are discussed. The URL of the Catalog is: http://cdaw.gsfc.nasa.gov/CME_list.
We study kinematics of 22 coronal mass ejections (CMEs) whose motion was traced from the gradual pre-acceleration phase up
to the post-acceleration stage. The peak accelerations in the studied sample range from 40, up to 7000m s−2, and are inversely proportional to the acceleration phase duration and the height range involved. Accelerations and velocities
are, on average, larger in CMEs launched from a compact source region. The acceleration phase duration is proportional to
the source region dimensions; i.e., compact CMEs are accelerated more impulsively. Such behavior is interpreted as a consequence of stronger Lorentz force and
shorter Alfvén time scales involved in compact CMEs (with stronger magnetic field and larger Alfvén speed being involved at
lower heights). CMEs with larger accelerations and velocities are on average wider, whereas the widths are not related to
the source region dimensions. Such behavior is explained in terms of the field pile-up ahead of the erupting structure, which
is more effective in the case of a strongly accelerated structure.
We present an overview of solar flares and associated phenomena, drawing upon a wide range of observational data primarily from the RHESSI era. Following an introductory discussion and overview of the status of observational capabilities, the article is split into topical sections which deal with different areas of flare phenomena (footpoints and ribbons, coronal sources, relationship to coronal mass ejections) and their interconnections. We also discuss flare soft X-ray spectroscopy and the energetics of the process. The emphasis is to describe the observations from multiple points of view, while bearing in mind the models that link them to each other and to theory. The present theoretical and observational understanding of solar flares is far from complete, so we conclude with a brief discussion of models, and a list of missing but important observations.
We analyze the relationship between the acceleration of coronal mass ejections (CMEs) and the energy release in associated
flares, employing a sample of 22 events in which the CME kinematics were measured from the pre-eruption stage up to the post-acceleration
phase. The data show a distinct correlation between the duration of the acceleration phase and the duration of the associated
soft X-ray (SXR) burst rise, whereas the CME peak acceleration and velocity are related to the SXR peak flux. In the majority
of events the acceleration started earlier than the SXR burst, and it is usually prolonged after the SXR burst maximum. In
about one half of the events the acceleration phase is very closely synchronized with the fastest growth of the SXR burst.
An additional one quarter of the events may be still considered as relatively well-synchronized, whereas in the remaining
quarter of the events there is a considerable mismatch. The results are interpreted in terms of the feedback relationship
between the CME dynamics and the reconnection process in the wake of the CME.
In this paper, we analyze the full evolution, from a few days prior to the eruption to the initiation, and the final acceleration and propagation, of the CME that occurred on 2008 April 26 using the unprecedented high cadence and multi-wavelength observations by STEREO. There existed frequent filament activities and EUV jets prior to the CME eruption for a few days. These activities were probably caused by the magnetic reconnection in the lower atmosphere driven by photospheric convergence motions, which were evident in the sequence of magnetogram images from MDI (Michelson Doppler Imager) onboard SOHO. The slow low-layer magnetic reconnection may be responsible for the storage of magnetic free energy in the corona and the formation of a sigmoidal core field or a flux rope leading to the eventual eruption. The occurrence of EUV brightenings in the sigmoidal core field prior to the rise of the flux rope implies that the eruption was triggered by the inner tether-cutting reconnection, but not the external breakout reconnection. During the period of impulsive acceleration, the time profile of the CME acceleration in the inner corona is found to be consistent with the time profile of the reconnection electric field inferred from the footpoint separation and the RHESSI 15-25 keV HXR flux curve of the associated flare. The full evolution of this CME can be described in four distinct phases: the build-up phase, initiation phase, main acceleration phase, and propagation phase. The physical properties and the transition between these phases are discussed, in an attempt to provide a global picture of CME dynamic evolution. Comment: 28 pages, 8 figures, accepted for publication in ApJ
We present a statistical analysis of 545 flare-associated CMEs and 104 non-flare CMEs observed in the heliocentric distance range 2–30 solar radii. We found that both data sets show quite similar characteristics, contradicting the concept of two distinct (flare/non-flare) types of CMEs. In both samples there is a significant fraction of CMEs showing a considerable acceleration or deceleration and both samples include a comparable ratio of fast and slow CMEs. We present kinematical curves of several fast non-flare CMEs moving at a constant speed or decelerating, i.e., behaving as expected for flare-associated CMEs. Analogously, we identified several slow flare-CMEs showing the acceleration peak beyond a height of 3 solar radii.
On the other hand, it is true that CMEs associated with major flares are on average faster and broader than non-flare CMEs and small-flare CMEs. There is a well-defined correlation between the CME speed and the importance of the associated flare. In this respect, the non-flare CMEs show characteristics similar to CMEs associated with flares of soft X-ray class B and C, which is indicative of a “continuum” of events rather than supporting the existence of two distinct CME classes. Furthermore, we inferred that CMEs whose source region cannot be identified with either flares or eruptive prominences are on average slowest. The results indicate that the magnetic reconnection taking place in the current sheet beneath the CME significantly influences the CME dynamics.
The Sun-Earth Connection Coronal and Heliospheric Investigation (SECCHI) com- bines a suite of optical telescopes with numerical modeling to capitalize on the unique viewpoint of the NASA Solar Terrestrial Relations Observatory (STEREO) mission to advance our understanding of the three-dimensional nature of the solar corona and coronal mass ejections. The instrument suite consists of two white-light coronagraphs (COR1 and COR2), an extreme ultraviolet disk imager (EUVI), collectively referred to as the Sun Centered Imaging Package (SCIP), and a heliospheric imager (HI). SEC- CHI will observe CMEs from their birth at the Sun, through the corona to their impact at Earth, from two different viewpoints away from the Sun-Earth line. SECCHI will also obtain stereoscopic observations of coronal structures such as loops and stream- ers. A coordinated modeling and data visualization effort will be used to interpret the images, and to integrate the SECCHI observations with the in-situ and radio measure- ments that will also be obtained from STEREO.
The most important observational characteristics of coronal mass ejections (CMEs) are summarized, emphasizing those aspects which are relevant for testing physical concepts employed to explain the CME take-off and propagation. In particular, the kinematics, scalings, and the CME-flare relationship are stressed. Special attention is paid to 3-dimensional (3-D) topology of the magnetic field structures, particularly to aspects related to the concept of semi-toroidal flux-rope anchored at both ends in the dense photosphere and embedded in the coronal magnetic arcade. Observations are compared with physical principles and concepts employed in explaining the CME phenomenon, and implications are discussed. A simple flux-rope model is used to explain various stages of the eruption. The model is able to reproduce all basic observational requirements: stable equilibrium and possible oscillations around equilibrium, metastable state and possible destabilization by an external disturbance, pre-eruptive gradual-rise until loss of equilibrium, possibility of fallback events and failed eruptions, relationship between impulsiveness of the CME acceleration and the source-region size, etc. However, it is shown that the purely ideal MHD process cannot account for highest observed accelerations which can attain values up to 10 km s−2. Such accelerations can be achieved if the process of reconnection beneath the erupting flux-rope is included into the model. Essentially, the role of reconnection is in changing the magnetic flux associated with the flux-rope current and supplying "fresh" poloidal magnetic flux to the rope. These effects help sustain the electric current flowing along the flux-rope, and consequently, reinforce and prolong the CME acceleration. The model straightforwardly explains the observed synchronization of the flare impulsive phase and the CME main-acceleration stage, as well as the correlations between various CME and flare parameters.
In this paper the Kolmogorov-Smirnov statistical test for the analysis of histograms is presented. The test is discussed for both the two-sample case (comparing fn1(X) to fn2 (X)) and the one-sample case (comparing fn1 (X) to f(X)). Presentation of the specific algorithmic steps involved is done through development of an example where the data are from an experiment discussed elsewhere in this issue. It is shown that the two histograms examined come from two different parent populations at the 99.9% confidence level.
Based on a sample of 1114 flares observed simultaneously in hard X-rays (HXR) by the BATSE instrument and in soft X-rays (SXR) by GOES, we studied several aspects of the Neupert effect and its interpretation in the frame of the electron-beam-driven evaporation model. In particular, we investigated the time differences ($\Delta t$) between the maximum of the SXR emission and the end of the HXR emission, which are expected to occur at almost the same time. Furthermore, we performed a detailed analysis of the SXR peak flux -- HXR fluence relationship for the complete set of events, as well as separately for subsets of events which are likely compatible/incompatibe with the timing expectations of the Neupert effect. The distribution of the time differences reveals a pronounced peak at $\Delta t = 0$. About half of the events show a timing behavior which can be considered to be consistent with the expectations from the Neupert effect. For these events, a high correlation between the SXR peak flux and the HXR fluence is obtained, indicative of electron-beam-driven evaporation. However, there is also a significant fraction of flares (about one fourth), which show strong deviations from $\Delta t = 0$, with a prolonged increase of the SXR emission distinctly beyond the end of the HXR emission. These results suggest that electron-beam-driven evaporation plays an important role in solar flares. Yet, in a significant fraction of events, there is also clear evidence for the presence of an additional energy transport mechanism other than the nonthermal electron beams, where the relative contribution is found to vary with the flare importance. Comment: 15 pages, 11 figures, to be published in A&A (2002)
The most important observational characteristics of coronal mass ejections (CMEs) are summarized, emphasizing those aspects which are relevant for testing physical concepts employed to explain the CME take-off and propagation. In particular, the kinematics, scalings, and the CME-flare relationship are stressed. Special attention is paid to 3-dimensional (3-D) topology of the magnetic field structures, particularly to aspects related to the concept of semi-toroidal flux-rope anchored at both ends in the dense photosphere and embedded in the coronal magnetic arcade. Observations are compared with physical principles and concepts employed in explaining the CME phenomenon, and implications are discussed. A simple flux-rope model is used to explain various stages of the eruption. The model is able to reproduce all basic observational requirements: stable equilibrium and possible oscillations around equilibrium, metastable state and possible destabilization by an external disturbance, pre-eruptive gradual-rise until loss of equilibrium, possibility of fallback events and failed eruptions, relationship between impulsiveness of the CME acceleration and the source-region size, etc. However, it is shown that the purely ideal MHD process cannot account for highest observed accelerations which can attain values up to 10 km s−2. Such accelerations can be achieved if the process of reconnection beneath the erupting flux-rope is included into the model. Essentially, the role of reconnection is in changing the magnetic flux associated with the flux-rope current and supplying "fresh" poloidal magnetic flux to the rope. These effects help sustain the electric current flowing along the flux-rope, and consequently, reinforce and prolong the CME acceleration. The model straightforwardly explains the observed synchronization of the flare impulsive phase and the CME main-acceleration stage, as well as the correlations between various CME and flare parameters.
We investigate the relationship between the main acceleration phase of coronal mass ejections (CMEs) and the particle acceleration in the associated flares as evidenced in Reuven Ramaty High Energy Solar Spectroscopic Imager non-thermal X-rays for a set of 37 impulsive flare-CME events. Both the CME peak velocity and peak acceleration yield distinct correlations with various parameters characterizing the flare-accelerated electron spectra. The highest correlation coefficient is obtained for the relation of the CME peak velocity and the total energy in accelerated electrons (c = 0.85), supporting the idea that the acceleration of the CME and the particle acceleration in the associated flare draw their energy from a common source, probably magnetic reconnection in the current sheet behind the erupting structure. In general, the CME peak velocity shows somewhat higher correlations with the non-thermal flare parameters than the CME peak acceleration, except for the spectral index of the accelerated electron spectrum, which yields a higher correlation with the CME peak acceleration (c –0.6), indicating that the hardness of the flare-accelerated electron spectrum is tightly coupled to the impulsive acceleration process of the rising CME structure. We also obtained high correlations between the CME initiation height h 0 and the non-thermal flare parameters, with the highest correlation of h 0 to the spectral index δ of flare-accelerated electrons (c 0.8). This means that CMEs erupting at low coronal heights, i.e., in regions of stronger magnetic fields, are accompanied by flares that are more efficient at accelerating electrons to high energies. In the majority of events (~80%), the non-thermal flare emission starts after the CME acceleration, on average delayed by 6 minutes, in line with the standard flare model where the rising flux rope stretches the field lines underneath until magnetic reconnection sets in. We find that the current sheet length at the onset of magnetic reconnection is 21 ± 7 Mm. The flare hard X-ray peaks are well synchronized with the peak of the CME acceleration profile, and in 75% of the cases they occur within ±5 minutes. Our findings provide strong evidence for the tight coupling between the CME dynamics and the particle acceleration in the associated flare in impulsive events, with the total energy in accelerated electrons being closely correlated with the peak velocity (and thus the kinetic energy) of the CME, whereas the number of electrons accelerated to high energies is decisively related to the CME peak acceleration and the height of the pre-eruptive structure.
Many properties of Coronal Mass Ejections (CMEs), such as size, location and brightness, have been determined from measurements of white light coronal observations. We expect the average properties derived from these measurements contain systematic inaccuracies due to projection effects and suggest that CME properties are most accurately determined for those events occurring near the plane-of-the-sky (i.e., over the solar limb as observed from Earth), where projection effects are minimized. A set of 111 such ``limb'' events have been identified in Solar Maximum Mission (SMM) white light observations through associations with Erupting Prominences at the Limb (EPLs), and X-ray and limb optical flares. These ``limb'' CMEs have greater average speeds (519 +/- 46 km/sec) and masses (4.5 +/- .5 × 1015 grams) than the average values obtained from all SMM CMEs, consistent with the expected behavior of projection effects. Only a very small percentage of ``limb'' CMEs are centered at high latitudes, suggesting there are many fewer ``true'' high latitude CMEs than has previously been reported. No ``limb'' CMEs have widths greater than 110°, consistent with the interpretation that very wide CMEs (i.e., halos) are actually events of more typical widths originating away from the solar limb and viewed in projection. Only a small percentage of ``limb'' CMEs have measured speeds below 200 km/sec, indicating there may be fewer ``true'' subsonic SMM CMEs than previously reported. The correlation detected between the kinetic energy of the ``limb'' CMEs and the peak intensity of the associated GOES X-ray flares, is stronger than was previously found using a set of CMEs of undetermined limb distances. All these results provide strong evidence that projection effects systematically influence the deduced properties of CME events.
The Extreme Ultraviolet Imager (EUVI) is part of the SECCHI instrument suite currently being developed for the NASA STEREO mission. Identical EUVI telescopes on the two STEREO spacecraft will study the structure and evolution of the solar corona in three dimensions, and specifically focus on the initiation and early evolution of coronal mass ejections (CMEs). The EUVI telescope is being developed at the Lockheed Martin Solar and Astrophysics Lab. The SECCHI investigation is led by the Naval Research Lab. The EUVI"s 2048 x 2048 pixel detectors have a field of view out to 1.7 solar radii, and observe in four spectral channels that span the 0.1 to 20 MK temperature range. In addition to its view from two vantage points, the EUVI will provide a substantial improvement in image resolution and image cadence over its predecessor SOHO-EIT, while complying with the more restricted mass, power, and volume allocations on the STEREO mission.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
We use a model of solar eruptions that combines a loss-of-equilibrium coronal mass ejection (CME) model with a multi-threaded flare loop model in order to understand the relationship between the CME kinematics, thermal energy release, and soft X-ray emissions in solar eruptions. We examine the correlation between CME acceleration and the peak soft X-ray flux in many modeled cases with different parameters, and find that the two quantities are well correlated. We also examine the timing of the peak acceleration and the light curve derivative, and find that these quantities tend to peak at similar times for cases where the magnetic field is high and the inflow Alfvén Mach number is fast. Finally, we study the relationship between the total thermal energy released in the model and the calculated peak soft X-ray flux of the resulting flare. We find that there is a power-law relationship between these two quantities, with F peak ~ E α, where α is between 2.54 and 1.54, depending on the reconnection rate. This finding has repercussions for the assumptions underlying the Neupert effect, in which the peak soft X-ray flux is assumed to be proportional to the thermal energy release.
In this paper we present the results of a statistical study of the accelerations of coronal mass ejections (CMEs). A CME usually undergoes a multiphased kinematic evolution, with a main acceleration phase characterized by a rapid increase of CME velocity in the inner corona, followed by a relatively smooth propagation phase characterized by a constant speed or a small residual acceleration in the outer corona. We study both the main acceleration and the residual acceleration for 50 CME events based on Large Angle Spectrometric Coronagraph (LASCO) observations. We find that the magnitude of the main acceleration has a wide distribution, from 2.8 to 4464.0 m s-2, with a median (average) value of 170.1 (330.9 m s-2), and a standard deviation of 644.8 m s-2, whereas the magnitude of the residual acceleration ranges only from -131.0 to 52.0 m s-2, with a median (average) value of 3.1 (0.9 m s-2) and a standard deviation of 25.3 m s-2. The duration of the main acceleration is also widely distributed, from 6 to 1200 minutes, with a median (average) value of 54 (180 minutes) and a standard deviation of 286 minutes.We find an intriguing scaling law between the acceleration magnitude (A) and the acceleration duration (T) over the entire parameter range of almost 3 orders of magnitude, which can be expressed as A (m s-2) = 10,000T-1 (minutes). The implications of these observational results on the issues of CME classification and CME modelings are discussed.
The "empirical Neupert effect" (ENE) is the observed temporal correlation of the hard X-ray (HXR) flux FHXR(t) with the time derivative of the soft X-ray (SXR) flux SXR(t) in many flares. This is widely taken to mean that the energetic electrons responsible for FHXR(t) by thick-target collisional bremsstrahlung are the main source of heating and mass supply (via chromospheric evaporation) of the SXR-emitting hot coronal plasma. If this interpretation were correct, one would expect better correlation between the beam power supply Pbeam(t), inferred from the HXR spectrum, and the actual power Pin(t) required to explain the SXR flux and spectrum, allowing for variations in both emission measure (EM) and temperature T, for radiative and conductive cooling losses, and for complexities of geometry like multiple loops. We call this the "theoretical Neupert effect" (TNE). To test if it is true that Pbeam(t) and Pin(t) inferred from data are better correlated than FHXR(t) and SXR(t), we use an approximate approach for a simple single-loop geometry and rough estimates of the particle and energy transport and apply the model to RHESSI and GOES data on four flares. We find that if the beam low cutoff energy E1 is taken as constant, the correlation of Pbeam(t), Pin(t) is no better than that of FHXR(t), SXR(t). While our modeling contains many approximations to cooling and other physics, ignored entirely from ENE data considerations, there seems to be no reason why their order-of-magnitude inclusion should make the TNE worse rather than better, although this should be checked by more accurate simulations. These results suggest that one or more of the following must be true: (1) fast electrons are not the main source of SXR plasma supply and heating, (2) the beam low cutoff energy varies with time, or (3) the TNE is strongly affected by source geometry. These options are discussed in relation to possible future directions for TNE research.
We analyze the relationship between the dynamics of the coronal mass ejection (CME) of 15 May 2001 and the energy release in the associated flare. The flare took place behind the east limb and was disclosed by a growing system of hot soft X-ray (SXR) loops that appeared from behind the limb around the onset of the rapid acceleration of the CME. The highly correlated behavior of the SXR light-curve derivative and the time profile of the CME acceleration reveals an intrinsic relationship between the CME dynamics and the flare energy release. Furthermore, we found that the CME acceleration peak occurs simultaneously with the fastest growth (100 km s-1) of X-ray loops, indicating that the reconnection plays an essential role in the eruption. Inspecting the CME/flare morphology we recognized in the Yohkoh-SXT images an oval feature that formed within the rising structure at the onset of the rapid acceleration phase, simultaneously with the appearance of the X-ray loops. The eruptive prominence was imbedded within the lower half of the oval, suggestive of a flux-rope/prominence magnetic configuration. We interpret the observed morphological evolution in terms of a reconnection process in the current sheet that presumably formed below the erupting flux-rope at the onset of the CME acceleration. Measurements of the tip-height of the cusped X-ray loop system and the height of the lower edge of the oval, enable us to trace the stretching of the current sheet. The initial distance between the oval and the loops amounted to 35 – 40 Mm. In about 1 h the inferred length of the current sheet increased to 150 – 200 Mm, which corresponds to a mean elongation speed of 35 – 45 km s-1. The results are discussed in the framework of CME models that include the magnetic reconnection below the erupting flux-rope.
We study the initiation and development of the limb coronal mass ejection (CME) of 15 May 2001, utilizing observations from Mauna Loa Solar Observatory (MLSO), the Solar and Heliospheric Observatory (SOHO), and Yohkoh. The pre-eruption images in various spectral channels show a quiescent prominence imbedded in the coronal void, being overlaid by the coronal arch. After the onset of rapid acceleration, this three-element structure preserved its integrity and appeared in the MLSO MK-IV coronagraph field of view as the three-part CME structure (the frontal rim, the cavity, and the prominence) and continued its motion through the field of view of the SOHO/LASCO coronagraphs up to 30 solar radii. Such observational coverage allows us to measure the relative kinematics of the three-part structure from the very beginning up to the late phases of the eruption. The leading edge and the prominence accelerated simultaneously: the rapid acceleration of the frontal rim and the prominence started at approximately the same time, the prominence perhaps being slightly delayed (4 – 6 min). The leading edge achieved the maximum acceleration a
max≈ 600 ± 150 m s−2 at a heliocentric distance 2.4 –2.5 solar radii, whereas the prominence reached a
max≈ 380± 50 m s−2, almost simultaneously with the leading edge. Such a distinct synchronization of different parts of the CME provides clear evidence that the entire magnetic arcade, including the prominence, erupts as an entity, showing a kind of self-similar expansion. The CME attained a maximum velocity of v
max≈ 1200 km s−1 at approximately the same time as the peak of the associated soft X-ray flare. Beyond about 10 solar radii, the leading edge of the CME started to decelerate at a≈−20 m s−2, most likely due to the aerodynamic drag. The deceleration of the prominence was delayed for 10 –30 min, which is attributed to its larger inertia.
On the charms of statistics, and how mechanical models resembling gambling machines offer a link to a handy way to characterize log-normal distributions, which can provide deeper insight into variability and probability - Normal or log-normal: That is the question.
Aims. Here, we study the relationship between flares and CMEs.Methods. For this purpose a statistical analysis of 578 flare-associated CMEs is presented. We considered two types of flare-associated CMEs: CMEs that follow and precede flare onset.Results. We shown that both samples have quite different characteristics. The first type of CMEs tends to be decelerated (median acceleration = –5.0 m s$^{-2}$), faster (median velocity = 519 km s$^{-1}$), and physically related to flares (a correlation coefficient between the energy of the CME and the peak of the X-ray flare = 0.80). The CMEs preceding associated flares are mostly accelerated (median acceleration = 5.4 m s$^{-2}$), slightly slower (median velocity = 487 km s$^{-1}$), and poorly related to flares (a correlation coefficient between the energy of the CME and the peak of the X-ray flare = 0.12).Conclusions. These two types of flare-associated CMEs demonstrate that magnetic reconnection, which influences the CME acceleration, could be significantly different in the two types of events.
This is a review of bootstrap methods, concentrating on basic ideas and applications rather than theoretical considerations. It begins with an exposition of the bootstrap estimate of standard error for one-sample situations. Several examples, some involving quite complicated statistical procedures, are given. The bootstrap is then extended to other measures of statistical accuracy such as bias and prediction error, and to complicated data structures such as time series, censored data, and regression models. Several more examples are presented illustrating these ideas. The last third of the paper deals mainly with bootstrap confidence intervals.
We discuss the following problem given a random sample X = (X
1, X
2,…, X
n) from an unknown probability distribution F, estimate the sampling distribution of some prespecified random variable R(X, F), on the basis of the observed data x. (Standard jackknife theory gives an approximate mean and variance in the case R(X, F) = \(\theta \left( {\hat F} \right) - \theta \left( F \right)\), θ some parameter of interest.) A general method, called the “bootstrap”, is introduced, and shown to work satisfactorily on a variety of estimation problems. The jackknife is shown to be a linear approximation method for the bootstrap. The exposition proceeds by a series of examples: variance of the sample median, error rates in a linear discriminant analysis, ratio estimation, estimating regression parameters, etc.
A study aimed at determining the fractions of impulsive and gradual flares that show the Neupert effect (the correlation observed in many flares between the time-integrated microwave and hard X-ray emissions and the soft X-ray emission light curve) and the implications that can be drawn about the different flare types is presented. The study is based on hard X-ray data from the Hard X-ray Burst Spectrometer on the Solar Maximum Mission and soft X-ray data from the GOES detector. It is concluded that the comparison of the soft X-ray time-derivative and the hard X-ray profile provides a simple and effective way of comparing the timing of the hard X-ray emission and the heating of the plasma.
Solar X ray line emission compared with microwave emission during flares
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