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Sequence of SDO/AIA 94 Å filtergrams. The first row displays one pre-flare image and two images recorded around the start of the flare. The second and third rows show snapshots during the main phase of the event. All images are displayed with logarithmic scaling, based on the minimum/maximum range of the image sequence.
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![Figure 9. From top to bottom: Magnetic-reconnection rate [ ˙ ϕ(t)]...](profile/Wolfgang-Polanec-2/publication/282181449/figure/fig6/AS:358796070277126@1462555057997/From-top-to-bottom-Magnetic-reconnection-rate-pht-determined-from-AIA-1600A1600A_Q320.jpg)
We study the energy-release process in the confined X1.6 flare that occurred
on 22 October 2014 in AR 12192. Magnetic-reconnection rates and reconnection
fluxes are derived from three different data sets: space-based data from the
Atmospheric Imaging Assembly (AIA) 1600 {\AA} filter onboard the Solar Dynamics
Observatory (SDO) and ground-based H$\a...
Similar publications
We demonstrate the sensitivity of magnetic energy and helicity computations regarding the quality of the underlying coronal magnetic field model. We apply the method of Wiegelmann & Inhester (2010) to a series of SDO/HMI vector magnetograms, and discuss nonlinear force-free (NLFF) solutions based on two different sets of the free model parameters....
Citations
... Tschernitz et al. (2018) found a high correlation (r = 0.9) of the peak values of the global reconnection rate with the SXR peak flux and its derivative over four orders of magnitude in GOES flare class. A correspondence has been also noted between the time evolution ofφ(t) and the time profiles of SXR derivative or HXR emission in the flare impulsive phase (e.g., Qiu 2009;Qiu et al. 2010;Miklenic et al. 2009;Veronig & Polanec 2015). However, Miklenic et al. (2009) found that in several eruptive flares the peak of the reconnection rate occurred ∼1−2 min earlier than the main HXR peak. ...
... To identify flaring pixels, we used a thresholding technique based on increases of >5.5 standard deviations in the intensitynormalized Hα images. Finally, for each time step we applied the derived mask of newly brightened flare pixels to the LOS magnetic field maps and calculated the magnetic flux swept by newly brightened flare pixels to obtain for each time step, t (for further details of the calculations see Veronig & Polanec 2015;Tschernitz et al. 2018). Figure 1 gives an overview of the 28 October 2003 flare evolution in USO Hα images along with the derived cumulated flare pixel masks (blue (red) for positive (negative) magnetic polarity) used to calculateφ(t). ...
Context. The 2003 October 28 (X17.2) eruptive flare was a unique event. The coronal electric field and the π -decay γ -ray emission flux displayed the highest values ever inferred for solar flares.
Aims. Our aim is to reveal physical links between the magnetic reconnection process, energy release, and acceleration of electrons and ions to high energies in the chain of the magnetic energy transformations in the impulsive phase of the solar flare.
Methods. The global reconnection rate, φ̇ ( t ), and the local reconnection rate (coronal electric field strength), E c ( r , t ), were calculated from flare ribbon separation in H α filtergrams and photospheric magnetic field maps. Then, HXRs measured by CORONAS-F/SPR-N and the derivative of the GOES SXR flux, İ SXR ( t ) were used as proxies of the flare energy release evolution. The flare early rise phase, main raise phase, and main energy release phase were defined based on temporal profiles of the above proxies. The available results of INTEGRAL and CORONAS-F/SONG observations were combined with Konus-Wind data to quantify the time behavior of electron and proton acceleration. Prompt γ -ray lines and delayed 2.2 MeV line temporal profiles observed with Konus-Wind and INTEGRAL/SPI were used to detect and quantify the nuclei with energies of 10−70 MeV.
Results. The magnetic-reconnection rates, φ̇ ( t ) and E c ( r , t ), follow a common evolutionary pattern with the proxies of the flare energy released into high-energy electrons. The global and local reconnection rates reach their peaks at the end of the main rise phase of the flare. The spectral analysis of the high-energy γ -ray emission revealed a close association between the acceleration process efficiency and the reconnection rates. High-energy bremsstrahlung continuum and narrow γ -ray lines were observed in the main rise phase when E c ( r , t ) of the positive (negative) polarity reached values of ∼120 V cm ⁻¹ (∼80 V cm ⁻¹ ). In the main energy release phase, the upper energy of the bremsstrahlung spectrum was significantly reduced and the pion-decay γ -ray emission appeared abruptly. We discuss the reasons why the change of the acceleration regime occurred along with the large-scale magnetic field restructuration of this flare.
Conclusions. The similarities between the proxies of the flare energy release with φ̇ ( t ) and E c ( r , t ) in the flare’s main rise phase are in accordance with the reconnection models. We argue that the main energy release and proton acceleration up to subrelativistic energies began just when the reconnection rate was going through the maximum, that is, following a major change of the flare topology.
... There have been several studies on the relationship between MFE and solar flaring activity (Sun et al. 2012(Sun et al. , 2015Choudhary et al. 2013;Tarr et al. 2013;Veronig & Polanec 2015;Jiang et al. 2016;Liu et al. 2016). Their studies have a couple of limitations: (1) their results are based on 2D magnetic field data, and (2) they did not use a large sample of data for the relationship. ...
In this Letter, we examine the relationship between 3D magnetic free energy (MFE) and flaring activity using 83 major solar flares (M-class and X-class) in nine solar active regions (ARs). For this, we use 998 nonlinear force-free field extrapolations compiled by the “Institute for Space-Earth Environmental Research Database” at Nagoya University. These ARs produced at least three major flares with distinct rising and peak phases of 3D MFE. For each phase, the solar flare occurrence rate (FOR) is calculated as a ratio of the number of flares to the duration. The major results from this study are summarized as follows. First, there is no clear linear correlation (CC = 0.15) between 3D MFE and flare peak flux. Second, the FOR (3.4 day ⁻¹ ) of the rising phase is a little higher than that (3.1 day ⁻¹ ) of the peak phase, depending on AR. Third, for several flares, there are noticeable decreases in 3D MFE, which correspond to the typical energy of a major flare (about 10 ³² erg). Fourth, it is interesting to note that there are noticeable enhancements in FORs at several local maxima of 3D MFE, which may be associated with flux emergence and/or shearing motions. Fifth, the flare index rates, which are defined as the summation of flaring activity divided by the duration, of rising and peak phases are 151 day ⁻¹ and 314 day ⁻¹ , respectively. Our results imply that the traditional and simple “storage and release” model does not apply to flare activities, and the random perturbation may be important for triggering flares.
... Therefore, the delay is either a consequence of the differences in cadences between the instruments or a physical mechanism causing the delay. Miklenic et al. (2007) and Veronig & Polanec (2015) found similar results when comparing reconnection rates with the HXR emission observed by RHESSI and GOES SXR emission rate. They interpret the newly brightened H α /EUV/UV flaring kernels, which are used to track the reconnection flux evolution and HXR emission to be produced by two types of nonthermal electrons. ...
Magnetic reconnection is understood to be the main physical process that facilitates the transformation of magnetic energy into heat, motion, and particle acceleration during solar eruptions. Yet, observational constraints on reconnection region properties and dynamics are limited due to a lack of high-cadence and high-spatial-resolution observations. By studying the evolution and morphology of postreconnected field-lines footpoints, or flare ribbons and vector photospheric magnetic field, we estimate the magnetic reconnection flux and its rate of change with time to study the flare reconnection process and dynamics of the current sheet above. We compare high-resolution imaging data to study the evolution of the fine structure in flare ribbons as ribbons spread away from the polarity inversion line. Using data from two illustrative events (one M- and X-class flare), we explore the relationship between the ribbon-front fine structure and the temporal development of bursts in the reconnection region. Additionally, we use the RibbonDB database to perform statistical analysis of 73 (C- to X-class) flares and identify quasiperiodic pulsation (QPP) properties using the Wavelet Transform. Our main finding is the discovery of QPP signatures in the derived magnetic reconnection rates in both example events and the large flare sample. We find that the oscillation periods range from 1 to 4 minutes. Furthermore, we find nearly cotemporal bursts in Hard X-ray (HXR) emission profiles. We discuss how dynamical processes in the current sheet involving plasmoids can explain the nearly cotemporal signatures of quasiperiodicity in the reconnection rates and HXR emission.
... Among other properties differing in confined and eruptive flares, average ribbon separation distances and ribbonpeak separation speeds tend to be smaller for confined flares (Kurokawa 1989;Su et al. 2007;Thalmann et al. 2015;Veronig & Polanec 2015;Hinterreiter et al. 2018). One explanation for this could be strong overlying fields in confined events, which prevent reconnecting the current sheet from moving upward. ...
... They found that in eruptive flares nonthermal HXR emission lags the EUV emission from flare ribbons, suggesting that eruptive flares have a gradual warm-up phase with lower nonthermal energy release efficiency. They also found that, on average, confined flares exhibit stronger magnetic shear and hightemperature components (up to 25 MK for up to 1 minute) at the onset, which is not present in eruptive flares (in agreement with the case study by Veronig & Polanec 2015). Note, however, that eruptive flares in the study by Qiu & Cheng (2022) had larger flare classes than confined events; ideally, flare samples of similar flare classes should be compared. ...
Solar flares sometimes lead to coronal mass ejections that directly affect Earth's environment. However, a large fraction of flares, including on solar-type stars, are confined flares. What are the differences in physical properties between confined and eruptive flares? For the first time, we quantify the thermodynamic and magnetic properties of hundreds of confined and eruptive flares of GOES class C5.0 and above, 480 flares in total. We first analyze large flares of GOES class M1.0 and above observed by the Solar Dynamics Observatory, 216 flares in total, including 103 eruptive and 113 confined flares, from 2010 until 2016 April; we then look at the entire data set of 480 flares above class C5.0. We compare GOES X-ray thermodynamic flare properties, including peak temperature and emission measure, and active-region (AR) and flare-ribbon magnetic field properties, including reconnected magnetic flux and peak reconnection rate. We find that for fixed peak X-ray flux, confined and eruptive flares have similar reconnection fluxes; however, for fixed peak X-ray flux confined flares have on average larger peak magnetic reconnection rates, are more compact, and occur in larger ARs than eruptive flares. These findings suggest that confined flares are caused by reconnection between more compact, stronger, lower-lying magnetic fields in larger ARs that reorganizes a smaller fraction of these regions’ fields. This reconnection proceeds at faster rates and ends earlier, potentially leading to more efficient flare particle acceleration in confined flares.
... Similarly, the correlation coefficient between peak X-ray flux and flare ribbon area was 0.58 for all flares, 0.48 for eruptive flares, and 0.53 for confined flares. These results are consistent with the findings of Veronig and Polanec (2015), Kazachenko et al. (2017), andTschernitz et al. (2018). ...
... Harra et al. (2016) showed that X-class flare duration has no correlation with flare class and type, however, their sample size is skewed towards eruptive flares due to the limited occurrence of confined X-class events due to CME usually associated with larger flares (Yashiro and Gopalswamy 2009;Youssef 2012). In another study, Veronig and Polanec (2015) discovered a significant correlation between the total magnetic reconnection flux against flare class, while Tschernitz et al. (2018) found a slightly higher correlation coefficient for eruptive flares as compared to confined flares. However, in the population sample size, there were extreme events included that could be regarded as outliers (Miklenic et al. 2009), and additionally, converting the variables to a logarithmic scale sometime could yield a higher correlation value as in this case. ...
... The chromosphere flare ribbon evolution images indicate the newly reconnected magnetic field. In line with Forbes and Priest (1984), Veronig and Polanec (2015), and Kazachenko et al. (2022), we use the newly brightened area of an image with an underlying magnetic field as a proxy for the total magnetic reconnection flux. The total magnetic reconnection flux cannot be derived directly but instead has to be obtained via an indirect approach. ...
Magnetic reconnection is a fundamental mechanism through which energy stored in magnetic fields is released explosively on a massive scale, they could be presented as eruptive or confined flares, depending on their association with coronal mass ejections (CMEs). Several previous works have concluded that there is no correlation between flare duration and flare class, however, their sample sizes are skewed towards B and C classes; they hardly represent the higher classes. Therefore, we studied a sample without extreme events in order to determine the correlation between flare duration and flare type (confined and eruptive). We examined 33 flares with classes between M5 to X5 within 45° of the disk centres, using data from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI). We find that the linear correlation between flare class against flare duration by full width half maximum (FWHM) in general is weak (\(r = 0.19\)); however, confined flares have a significant correlation (\(r = 0.58\)) compared to eruptive types (\(r = 0.08\)). Also, the confined M class flares’ average duration is less than half of the eruptive flares. Similarly, confined flares have a higher correlation (\(r = 0.89\)) than eruptive flares (\(r = 0.60\)) between flare classes against magnetic reconnection flux. In this work, a balanced sample size between flare types is an important strategy for obtaining a reliable quantitative comparison.
... We can see from Figure 14 that the motion of the ribbons is very slow and the displacement is small, confirming what has been observed by other authors about the ribbon separation during this flare (Thalmann et al. 2015;Veronig & Polanec 2015). It is worth mentioning the small displacement of the flare ribbon observed in the region of the magnetic polarity intrusion. ...
... Indeed, by comparing the magnetic field line connectivity with the temporal evolution of the isophotes of the flare ribbons observed by IRIS, we could expect that the interaction between the positive intrusion observed within the IBIS FOV and the overlying magnetic field might have had a role during the flare, and therefore the fact that we do not observe photospheric B LOS changes in this area is noteworthy. In this respect, taking into account that the isophotes' distribution with time (see Figure 14) indicates quite a slow evolution of the ribbons, we recall that Veronig & Polanec (2015) and Thalmann et al. (2015) found that the considered event shows a great initial separation of the ribbon, but no significant displacement during the flare. ...
We report on observations acquired by the Interferometric Bidimensional Spectropolarimeter (IBIS) during SOL2014-10-22T14:02, an X1.6 flare that occurred in active region NOAA 12192, taken in the Fe i 617.30 nm and Ca ii 854.2 nm line profiles. We analyze polarization signatures in the Stokes profiles of the two lines across one of the flare ribbons. Focusing our attention on the chromospheric signals and using the weak-field approximation (WFA), we study the temporal variation of the line-of-sight (LOS) magnetic field. We find variations of the magnetic field or the opacity along the flare ribbon, in most cases within the first 3 minutes of the observation just after the flare peak, during the tail of the flare impulsive phase. This result was validated by the STiC inversion of the pixels used for the WFA analysis. The analysis of the photospheric magnetic field shows that in this layer, the LOS magnetic field does not show the same changes observed in the chromosphere in the selected pixels, nor clear evidence of changes along the polarity inversion line around a magnetic polarity intrusion. In this respect, we also find that the temporal observing window is not suitable for assessing the presence of stepwise changes. The nonlinear force-free field extrapolations, together with the analysis of the ribbons’ isophotes obtained from Interface Region Imaging Spectrograph data, suggest that the region corresponding to the magnetic intrusion observed by IBIS is characterized by a complex magnetic connectivity and is almost cospatial with the area affected by the initial energy release.
... A certain correlation has been established between the time evolution of the magneticfield reconnection rate, the time profiles of SXR derivative or HXR emission in the flare impulsive phase (e.g., Qiu, 2009;Miklenic, Veronig, and Vršnak, 2009;Veronig and Polanec, 2015). In the confined flare of 2014 October 22 (X1.6) ...
... In the confined flare of 2014 October 22 (X1.6) Veronig and Polanec (2015) showed that the RHESSI HXR count rates reached a peak level within a one-minute interval close to the maximum of the reconnection rate. Conversely Miklenic, Veronig, and Vršnak (2009) found that the reconnection rate maximum in eruptive flares is observed somewhat ahead (1 -2 min) of the main peak in the HXR. ...
We analyze here the impulsive phase of the 2001 August 25 eruptive flare (X5.3, S21, E38) in order to reveal the link of the time evolution of the magnetic-field reconnection rate φ˙(t) with the energy-release process, as quantified by electron and proton acceleration to high energies. Hard X-rays and γ-rays from 150 keV to 100 MeV were observed by the SONG (SOlar Neutrons and Gamma) detector onboard the CORONAS-F (Complex ORbital ObservatioNs of the Active Sun) mission. The soft X-ray derivative dISXR/dt was used as a proxy for the flare energy release that revealed itself as a sequence of acceleration pulses. The reconnection rate φ˙(t) was calculated previously from flare-ribbon observations in EUV and coaligned magnetic-field maps. The γ-ray emission spectra were obtained from SONG data. All spectra contain both bremsstrahlung and γ-ray lines. The bremsstrahlung spectrum extends to tens of MeV. The pion-decay gamma-ray emission, being a manifestation of proton acceleration to subrelativistic energies, appeared for the first time in the time interval of the φ˙(t) maximum. This maximum was ahead of the maxima of dISXR/dt as well as of all other emissions by about one minute. Proton acceleration to subrelativistic energies is confirmed by detection of solar neutrons by SONG and the Chacaltaya neutron monitor.
... To identify and segment the flare ribbon pixels, we apply a threshold-based method, following Veronig & Polanec (2015) and Tschernitz et al. (2018). More precisely, we determine the lowest intensity maximum I m across the entire set of AIA maps, which usually corresponds to a time of low solar activity. ...
Aims. We analyze the complete chain of effects – from the Sun to Earth – caused by a solar eruptive event in order to better understand the dynamic evolution of magnetic-field-related quantities in interplanetary space, in particular that of magnetic flux and helicity.
Methods. We study a series of connected events – a confined C4.5 flare, a flare-less filament eruption, and a double-peak M-class flare – that originated in NOAA active region (AR) 12891 on late 2021 November 1 and early 2021 November 2. We deduce the magnetic structure of AR 12891 using stereoscopy and nonlinear force-free (NLFF) magnetic field modeling, allowing us to identify a coronal flux rope and to estimate its axial flux and helicity. Additionally, we compute reconnection fluxes based on flare ribbon and coronal dimming signatures from remote sensing imagery. Comparison to corresponding quantities for the associated magnetic cloud (MC) deduced from in situ measurements from Solar Orbiter and near-Earth spacecraft allows us to draw conclusions on the evolution of the associated interplanetary coronal mass ejection (CME). The latter analysis is aided by the application of geometric fitting techniques (graduated cylindrical shell modeling; GCS) and interplanetary propagation models (drag-based ensemble modeling; DBEM) to the interplanetary CME.
Results. NLFF modeling suggests the magnetic structure of the host AR was in the form of a left-handed (negative-helicity) flux rope reaching altitudes of 8−10 Mm above photospheric levels, which is in close agreement with the corresponding stereoscopic estimate. GCS and DBEM modeling suggest that the ejected flux rope propagated in a self-similar expanding manner through interplanetary space. Comparison of magnetic fluxes and helicities processed by magnetic reconnection in the solar source region and the respective budgets of the MC indicate a considerable contribution from the eruptive process, though the pre-eruptive budgets also appear to be relevant.
... Bamba et al. (2017) studied the precursor conditions to this event in order to determine triggering conditions in the chromosphere and photospheric magnetic field. Veronig & Polanec (2015) attempted to quantify the magnetic reconnection flux and rate. utilized data from the Interface Region Imaging Spectrometer (IRIS;De Pontieu et al. 2014) and RHESSI instruments to study Doppler velocities in Fe XXI and C I and HXR intensities. ...
We studied an X1.6 solar flare produced by NOAA Active Region 12602 on 2014 October 22. The entirety of this event was covered by RHESSI, IRIS, and Hinode/EIS, allowing analysis of the chromospheric response to a nonthermal electron driver. We derived the energy contained in nonthermal electrons via RHESSI spectral fitting and linked the time-dependent parameters of this call to the response in Doppler velocity, density, and nonthermal width across a broad temperature range. The total energy injected was 4.8 × 10 ³⁰ erg and lasted 352 s. This energy drove explosive chromospheric evaporation, with a delineation in both Doppler and nonthermal velocities at the flow reversal temperature, between 1.35 and 1.82 MK. The time of peak electron injection (14:06 UT) corresponded to the time of highest velocities. At this time, we found 200 km s ⁻¹ blueshifts in the core of Fe xxiv , which is typically assumed to be at rest. Shortly before this time, the nonthermal electron population had the shallowest spectral index (≈6), corresponding to the peak nonthermal velocity in Si iv and Fe xxi . Nonthermal velocities in Fe xiv , formed near the flow reversal temperature, were low and not correlated with density or Doppler velocity. Nonthermal velocities in ions with similar temperatures were observed to increase and correlate with Doppler velocities, implying unresolved flows surrounding the flow reversal point. This study provides a comprehensive, time-resolved set of chromospheric diagnostics for a large X-class flare, along with a time-resolved energy injection profile, ideal for further modeling studies.
... Bamba et al. (2017) studied the precursor conditions to this event in order to determine triggering conditions in the chromosphere and photospheric magnetic field. Veronig & Polanec (2015) attempted to quantify the magnetic reconnection flux and rate. utilized data from the Interface Region Imaging Spectrometer (IRIS ;De Pontieu et al. 2014) and RHESSI instruments to study Doppler velocities in Fe XXI and C I, and HXR intensities. ...
We studied an X1.6 solar flare produced by NOAA AR 12602 on 2014 October 22. The entirety of this event was covered by RHESSI, IRIS, and Hinode/EIS, allowing analysis of the chromospheric response to a nonthermal electron driver. We derived the energy contained in nonthermal electrons via RHESSI spectral fitting, and linked the time-dependent parameters of this call to the response in Doppler velocity, density, and nonthermal width across a broad temperature range. The total energy injected was $4.8\times10^{30}$ erg, and lasted $352$ seconds. This energy drove explosive chromospheric evaporation, with a delineation in both Doppler and nonthermal velocities at the flow reversal temperature, between 1.35--1.82 MK. The time of peak electron injection (14:06 UT) corresponded to the time of highest velocities. At this time, we found 200 km s$^{-1}$ blueshifts in the core of Fe XXIV, which is typically assumed to be at rest. Shortly before this time, the nonthermal electron population had the shallowest spectral index ($\approx$ 6), corresponding to the peak nonthermal velocity in Si IV and Fe XXI. Nonthermal velocities in Fe XIV, formed near the flow reversal temperature were low, and not correlated with density or Doppler velocity. Nonthermal velocities in ions with similar temperatures were observed to increase and correlate with Doppler velocities, implying unresolved flows surrounding the flow reversal point. This study provides a comprehensive, time-resolved set of chromospheric diagnostics for a large X-class flare, along with a time-resolved energy injection profile, ideal for further modeling studies.
