Fig 2 - uploaded by Lucie Green
Content may be subject to copyright.
Solar active region NOAA 11158 at ∼ 06:28 UT on 2011 February 14. (a,b) Helicity flux density distributions in units of 10 7 Wb 2 m −2 s −1 with the same color scale: (a) G θ and (b) G Φ maps. All photospheric maps are overplotted with ±500 gauss isocontours of B z .
Source publication
Measuring the magnetic helicity distribution in the solar corona can help in
understanding the trigger of solar eruptive events because magnetic helicity is
believed to play a key role in solar activity due to its conservation property.
A new method for computing the photospheric distribution of the helicity flux
was recently developed. This method...
Contexts in source publication
Context 1
... full photospheric xy-domain of the NLFFF extrapolation was considered to derive the helicity flux density maps displayed in Figure 2. In this domain, the closed magnetic field -for which G Φ has been computed -encloses 73% of the total un- signed magnetic flux. ...
Context 2
... compared the total fluxes computed from both G θ and G Φ maps displayed in Figure 2. The helicity flux of the closed mag- netic field and the total helicity flux computed with the proxy G θ are 3.7 × 10 21 Wb 2 s −1 and 2.3 × 10 21 Wb 2 s −1 , respectively. ...
Context 3
... Figure 2b, the G Φ map also displays mixed signals. This implies that there are real mixed signs of the helicity flux in the AR, as found in previous studies (e.g., Jing et al. 2012;Vemareddy et al. 2012). ...
Context 4
... implies that there are real mixed signs of the helicity flux in the AR, as found in previous studies (e.g., Jing et al. 2012;Vemareddy et al. 2012). However, the distribution is different from the results of the G θ map (Figure 2a Considering only the closed magnetic field, we summed the positive and then the negative helicity flux signals for both G θ and G Φ . We found that the ratio of these fluxes computed with G Φ compared with G θ are 0.84 and 0.57, respectively. ...
Context 5
... this figure, each magnetic field line is colored according to the associated true helicity flux density computed from Equa- tion (4). The 3D representation of the true helicity flux density shows us that the helicity flux density map (Figure 2b) is the re- sult of two magnetic structures of strong opposite helicity flux: an inner system with positive helicity flux overlaid by an outer system of negative helicity flux. ...
Similar publications
A filament eruption was observed with the Siberian Solar Radio Telescope
(SSRT) on June 23 2012, starting around 06:40 UT, beyond the West limb. The
filament could be followed in SSRT images to heights above 1 Rs, and coincided
with the core of the CME, seen in LASCO C2 images. We discuss briefly the
dynamics of the eruption: the top of the filamen...
The details of volcanic plume source conditions or internal structure cannot readily be revealed by simple visual images or other existing remote imaging techniques. For example, one predominant observable quantity, the spreading rate in steady or quasi-steady volcanic plumes, is independent of source buoyancy flux. However, observable morphologica...
![Fig. 1.— A drizzled image of the combined 1994 and 1995 HST WFPC2 [NII]...](profile/Michael-Shara/publication/252932745/figure/fig1/AS:298211018330116@1448110455799/A-drizzled-image-of-the-combined-1994-and-1995-HST-WFPC2-NII-imaging-of-T-Pyx_Q320.jpg)
Hubble Space Telescope} images of the ejecta surrounding the nova T Pyxidis
resolve the emission into more than two thousand bright knots. We simulate the
dynamical evolution of the ejecta from T Pyxidis during its multiple eruptions
over the last 150 years using the adaptive mesh refinement capability of the
gas dynamics code Ramses. We demonstrat...
We present the observations of compound flux rope formation via merging of
two nearby filament channels, associated dynamics and its stability that
occurred on 2014 January 1 using multiwavelength data. We have also discussed
the dynamics of cool and hot plasma moving along the newly formed compound flux
rope. The merging started after the interact...
A filament eruption was observed on October 31, 2010 in the images recorded
by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic
Observatory (SDO) in its Extreme Ultra-Violet (EUV) channels. The filament
showed a slow rise phase followed by a fast rise and was classified to be an
asymmetric eruption. In addition, multiple localized...
Citations
... In observations, the analysis of the helicity eruptivity index required the knowledge of the magnetic field in the whole studied domain. As Linan et al. (2018) demonstrated, H j and H pj cannot be estimated from their flux through the photosphere, unlike what is frequently done with relative magnetic helicity (e.g. as in Chae 2001;Nindos et al. 2003;Pariat et al. 2005Pariat et al. , 2006Dalmasse et al. 2013Dalmasse et al. , 2014Dalmasse et al. , 2018Liokati et al. 2022). Estimates of H j and H pj must therefore rely on magnetic extrapolation of the coronal field from photospheric measurements (c.f. ...
Context. While non-potential (free) magnetic energy is a necessary element of any active phenomenon in the solar corona, its role as a marker of the trigger of the eruptive process remains elusive. Meanwhile, recent analyses of numerical simulations of solar active events have shown that quantities based on relative magnetic helicity could highlight the eruptive nature of solar magnetic systems.
Aims. Based on the unique decomposition of the magnetic field into potential and non-potential components, magnetic energy and helicity can also both be uniquely decomposed into two quantities. Using two 3D magnetohydrodynamics parametric simulations of a configuration that can produce coronal jets, we compare the dynamics of the magnetic energies and of the relative magnetic helicities.
Methods. Both simulations share the same initial setup and line-tied bottom-boundary driving profile. However, they differ by the duration of the forcing. In one simulation, the system is driven sufficiently so that a point of no return is passed and the system induces the generation of a helical jet. The generation of the jet is, however, markedly delayed after the end of the driving phase; a relatively long phase of lower-intensity reconnection takes place before the jet is eventually induced. In the other reference simulation, the system is driven during a shorter time, and no jet is produced.
Results. As expected, we observe that the jet-producing simulation contains a higher value of non-potential energy and non-potential helicity compared to the non-eruptive system. Focussing on the phase between the end of the driving-phase and the jet generation, we note that magnetic energies remain relatively constant, while magnetic helicities have a noticeable evolution. During this post-driving phase, the ratio of the non-potential to total magnetic energy very slightly decreases while the helicity eruptivity index, which is the ratio of the non-potential helicity to the total relative magnetic helicity, significantly increases. The jet is generated when the system is at the highest value of this helicity eruptivity index. This proxy critically decreases during the jet-generation phase. The free energy also decreases but does not present any peak when the jet is being generated.
Conclusions. Our study further strengthens the importance of helicities, and in particular of the helicity eruptivity index, to understand the trigger mechanism of solar eruptive events.
... A quantity that has shown promise in advancing our knowledge of which CME processes are the key ones is magnetic helicity (e.g., Green et al. 2002;Démoulin 2007;Dalmasse et al. 2013;Yeates & Hornig 2016;Patsourakos & Georgoulis 2017). Magnetic helicity is a signed scalar quantity that measures the 3D complexity of a magnetic field within a volume, and its cascade to larger size scales could help build eruptive structures. ...
Coronal mass ejections are among the Sun’s most energetic activity events yet the physical mechanisms that lead to their occurrence are not yet fully understood. They can drive major space weather impacts at Earth, so knowing why and when these ejections will occur is required for accurate space weather forecasts. In this study we use a 4 day time series of a quantity known as the helicity ratio, ∣ H J ∣/∣ H V ∣ (helicity of the current-carrying part of the active region field to the total relative magnetic helicity within the volume), which has been computed from nonlinear force-free field extrapolations of NOAA active region 11158. We compare the evolution of ∣ H J ∣/∣ H V ∣ with the activity produced in the corona of the active region and show this ratio can be used to indicate when the active region is prone to eruption. This occurs when ∣ H J ∣/∣ H V ∣ exceeds a value of 0.1, as suggested by previous studies. We find the helicity ratio variations to be more pronounced during times of strong flux emergence, collision and reconnection between fields of different bipoles, shearing motions, and reconfiguration of the corona through failed and successful eruptions. When flux emergence, collision, and shearing motions have lessened, the changes in helicity ratio are somewhat subtle despite the occurrence of significant eruptive activity during this time.
... This is commonly based on the decomposition of the flux into two components: a shear component provided by photospheric tangential flow, and a vertical component linked with normal flows due to emergence (Bi et al. 2018). At the same time, new methods for properly measuring helicities in the solar corona are still being developed (Dalmasse et al. 2013(Dalmasse et al. , 2014(Dalmasse et al. , 2018Valori et al. 2016;Guo et al. 2017;Moraitis et al. 2018;Gosain & Brandenburg 2019). For instance, new analytic expressions for the helicity transport allow us to estimate the injection of relative magnetic helicity into the solar atmosphere over an entire solar cycle (Hawkes & Yeates 2019;Pipin et al. 2019). ...
Context. Conservation properties of magnetic helicity and energy in the quasi-ideal and low- β solar corona make these two quantities relevant for the study of solar active regions and eruptions.
Aims. Based on a decomposition of the magnetic field into potential and nonpotential components, magnetic energy and relative helicity can both also be decomposed into two quantities: potential and free energies, and volume-threading and current-carrying helicities. In this study, we perform a coupled analysis of their behaviors in a set of parametric 3D magnetohydrodynamic (MHD) simulations of solar-like eruptions.
Methods. We present the general formulations for the time-varying components of energy and helicity in resistive MHD. We calculated them numerically with a specific gauge, and compared their behaviors in the numerical simulations, which differ from one another by their imposed boundary-driving motions. Thus, we investigated the impact of different active regions surface flows on the development of the energy and helicity-related quantities.
Results. Despite general similarities in their overall behaviors, helicities and energies display different evolutions that cannot be explained in a unique framework. While the energy fluxes are similar in all simulations, the physical mechanisms that govern the evolution of the helicities are markedly distinct from one simulation to another: the evolution of volume-threading helicity can be governed by boundary fluxes or helicity transfer, depending on the simulation.
Conclusions. The eruption takes place for the same value of the ratio of the current-carrying helicity to the total helicity in all simulations. However, our study highlights that this threshold can be reached in different ways, with different helicity-related processes dominating for different photospheric flows. This means that the details of the pre-eruptive dynamics do not influence the eruption-onset helicity-related threshold. Nevertheless, the helicity-flux dynamics may be more or less efficient in changing the time required to reach the onset of the eruption.
... Then, they proposed an alternative proxy of the helicity flux density, G Φ , which takes into account the magnetic field connectivity and thus requires 3D magnetic extrapolations. Dalmasse et al. (2013Dalmasse et al. ( , 2014) developed a method to compute G Φ and applied it to observational data of the complex flaring AR NOAA 11158 ( Fig. 14), showing that this proxy reliably and accurately maps the distribution of photospheric helicity injection. ...
Strong solar flares and coronal mass ejections, here defined not only as the bursts of electromagnetic radiation but as the entire process in which magnetic energy is released through magnetic reconnection and plasma instability, emanate from active regions (ARs) in which high magnetic non-potentiality resides in a wide variety of forms. This review focuses on the formation and evolution of flare-productive ARs from both observational and theoretical points of view. Starting from a general introduction of the genesis of ARs and solar flares, we give an overview of the key observational features during the long-term evolution in the pre-flare state, the rapid changes in the magnetic field associated with the flare occurrence, and the physical mechanisms behind these phenomena. Our picture of flare-productive ARs is summarized as follows: subject to the turbulent convection, the rising magnetic flux in the interior deforms into a complex structure and gains high non-potentiality; as the flux appears on the surface, an AR with large free magnetic energy and helicity is built, which is represented by
δ
-sunspots, sheared polarity inversion lines, magnetic flux ropes, etc; the flare occurs when sufficient magnetic energy has accumulated, and the drastic coronal evolution affects magnetic fields even in the photosphere. We show that the improvement of observational instruments and modeling capabilities has significantly advanced our understanding in the last decades. Finally, we discuss the outstanding issues and future perspective and further broaden our scope to the possible applications of our knowledge to space-weather forecasting, extreme events in history, and corresponding stellar activities.
... Further investigations on different magnetic field simulations are required to capture the dynamics of this quantity. More generally, magnetic helicity needs to be further understood through fundamental studies on its mathematical properties (Oberti & Ricca 2018), on its physical interpretation (Yeates & Hornig 2013Russell et al. 2015;Aly 2018), and on its proper measurement in the solar corona ( Dalmasse et al. 2013Dalmasse et al. , 2014Dalmasse et al. , 2018Valori et al. 2016;Guo et al. 2017;Moraitis et al. 2018). ...
Relative magnetic helicity is a gauge-invariant quantity suitable for the study of the magnetic helicity content of heliospheric plasmas. Relative magnetic helicity can be decomposed uniquely into two gauge-invariant quantities, the magnetic helicity of the nonpotential component of the field and a complementary volume-threading helicity. Recent analysis of numerical experiments simulating the generation of solar eruptions have shown that the ratio of the nonpotential helicity to the total relative helicity is a clear marker of the eruptivity of the magnetic system, and that the high value of that quantity could be a sufficient condition for the onset of the instability generating the eruptions. The present study introduces the first analytical examination of the time variations of these nonpotential and volume-threading helicities. The validity of the analytical formulae derived are confirmed with analysis of 3D magnetohydrodynamics (MHD) simulations of solar coronal dynamics. Both the analytical investigation and the numerical application show that, unlike magnetic helicity, the nonpotential and the volume-threading helicities are not conserved quantities, even in the ideal MHD regime. A term corresponding to the transformation between the nonpotential and volume-threading helicities frequently dominates their dynamics. This finding has an important consequence for their estimation in the solar corona: unlike with relative helicity, their volume coronal evolution cannot be ascertained by the flux of these quantities through the volume's boundaries. Only techniques extrapolating the 3D coronal field will enable both the proper study of the nonpotential and volume-threading helicities and the observational analysis of helicity-based solar-eruptivity proxies. © 2018. The American Astronomical Society. All rights reserved.
... We have employed DAI analysis to study flares in the AR NOAA 11158. The evolution of the magnetic field in this AR have been extensively studied, e.g., regarding the magnetic structure ( Sun et al. 2012;Toriumi et al. 2013;Malanushenko et al. 2014;Zhao et al. 2014), magnetic helicity ( Jing et al. 2012;Dalmasse et al. 2013;Tziotziou et al. 2013;Zhang et al. 2016), photospheric field ( Liu et al. 2012;Petrie 2012Petrie , 2013Wang et al. 2012), magnetic energy ( Sun et al. 2012;Aschwanden et al. 2014;Malanushenko et al. 2014), magnetic twist ( Inoue et al. 2011;Sun et al. 2012;Liu et al. 2013;Inoue et al. 2014a;Malanushenko et al. 2014;Zhao et al. 2014), and others. Observational studies suggested that tether-cutting reconnection happened in the AR during the M6.6 ( Liu et al. 2012) and X2.2 ( Wang et al. 2012;Liu et al. 2013) flares. ...
... -(c). The general morphologies and the locations of the high-twist fields are also in agreement with many previous studies(Jing et al. 2012;Sun et al. 2012;Dalmasse et al. 2013;Inoue et al. 2013Inoue et al. , 2014a;Liu et al. 2013;Wang et al. 2013;Aschwanden et al. 2014;Malanushenko et al. 2014;Zhao et al. 2014). UnlikeZhao et al. (2014)who could identify the twisted flux rope from the topology of the reconstructed coronal field, we could not find an obvious topological signature of a flux rope existing in our NLFFF during our analysis time window. ...
... However, our result is consistent with other NLFFF results (Jing et al. 2012;Sun et al. 2012;Liu et al. 2013;Wang et al. 2013;Inoue et al. 2014a;Malanushenko et al. 2014). The high-twist region in our result is also in agreement with the region with high helicity flux (Dalmasse et al. 2013) and the location of the flare ribbons (Bamba et al. 2013;Liu et al. 2013), as well as the high current density region(Janvier et al. 2014).Figures 1(g)-(i)show the evolution of the twist distribution map, with the magnetic twist of the field lines plotted at the footpoints of field lines according to a color scale. This shows ...
Coronal magnetic fields are responsible for the onset of solar flares and solar eruptions. However, the type of magnetic field parameters that can be used to measure the critical condition for a solar eruption is still unclear. As an effort to understand the possible condition for a solar flare, we have examined the nondimensional parameter κ introduced by Ishiguro & Kusano, which contains information about magnetic twist distribution and magnetic flux in an active region (AR). We introduce a new parameter κ∗, as a proxy for κ, and we have analyzed the evolution of κ∗ during the flaring period of an AR using the nonlinear force-free field extrapolated from the photospheric vector magnetic field data. Using data from the Solar Dynamics Observatory/Helioseismic and Magnetic Imager, we have calculated κ∗ for the AR NOAA 11158 during its three-day flaring period. We found that κ∗ increased to a certain level before two large flares and decreased significantly after their onset. The results suggest that κ∗ may be used as an indicator of the necessary condition for the onset of a solar eruption in the AR. Based on this result, we propose a new method to assess the possibility of a large solar eruption from an AR by combining the parameter κ∗ and information about the magnetic energy of the AR. © 2018. The American Astronomical Society. All rights reserved..
... Then we computed helicity flux and accumulation with Equation 3 and Equations 5 -6, respectively. Moreover, to check the spatial distribution of helicity injection rate in the region of filament activity, we also calculated the connectivity-based helicity flux density distribution G φ with Equations 7 and 8 (Dalmasse et al., 2013;Bi et al., 2015). The connectivity information over the computed region is obtained from a linear force free field (LFFF) extrapolation (Alissandrakis, 1981;Gary, 1989). ...
... It is clear that both the G θ and G φ maps display mixed signals, but negative signals mainly appear centered around the positive-polarity magnetic element of the dipole, P, where the filament rooted its positive-polarity ends. Compared with the G θ maps, some weak opposite-polarity signals appear in G φ maps, as found in previous studies (Dalmasse et al., 2013;Bi et al., 2015). In particular, these negative signal lasted for more than 10 hours, implying that persistent negative helicity was injected around the positive-polarity ends of the forming filament. ...
We present observations of the formation process of a small-scale filament on the quiet Sun during 5 – 6 February 2016 and investigate its formation cause. Initially, a small dipole emerged, and its associated arch filament system was found to reconnect with overlying coronal fields accompanied by numerous extreme ultraviolet bright points. When the bright points faded, many elongated dark threads formed and bridged the positive magnetic element of the dipole and the external negative network fields. Interestingly, an anticlockwise photospheric rotational motion (PRM) set in within the positive endpoint region of the newborn dark threads following the flux emergence and lasted for more than 10 hours. Under the drive of the PRM, these dispersive dark threads gradually aligned along the north-south direction and finally coalesced into an inverse S-shaped filament. Consistent with the dextral chirality of the filament, magnetic helicity calculations show that an amount of negative helicity was persistently injected from the rotational positive magnetic element and accumulated during the formation of the filament. These observations suggest that twisted emerging fields may lead to the formation of the filament via reconnection with pre-existing fields and release of its inner magnetic twist. The persistent PRM might trace a covert twist relaxation from below the photosphere to the low corona.
... Then we computed helicity flux and accumulation with Equation 3 and Equation 5-6, respectively. Moreover, to check the spatial distribution of helicity injection rate in the region of filament activity, we also calculated the connectivity-based helicity flux density distribution G φ with Equation 7 and 8 (Dalmasse et al., 2013;Bi et al., 2015). The connectivity information over the computed region The red circle circumscribes the supergranular cell whose mean velocity was around 0.28 km s −1 . is obtained from a linear force free field (LFFF) extrapolation (Alissandrakis, 1981;Gary, 1989). ...
... It is clear that both the G θ and G φ maps display mixed signals, but negative signals mainly appear centering around the positive-polarity magnetic element of the dipole, P, where the filament rooted its positive-polarity ends. Compared with the G θ maps, some weak opposite signals appear in G φ maps, as found in previous studies (Dalmasse et al., 2013;Bi et al., 2015). In particular, these negative signal lasted for more than 10 hours, implying that persistent negative helicity was injected around the positive-polarity ends of the forming filament. ...
We present observations of the formation process of a small-scale filament on the quiet Sun during 5-6 February 2016 and investigate its formation cause. Initially, a small dipole emerged and its associated arch filament system was found to reconnect with overlying coronal fields accompanied by numerous EUV bright points. When bright points faded out, many elongated dark threads formed bridging the positive magnetic element of dipole and external negative network fields. Interestingly, an anti-clockwise photospheric rotational motion (PRM) set in within the positive endpoint region of newborn dark threads following the flux emergence and lasted for more than 10 hours. Under the drive of the PRM, these dispersive dark threads gradually aligned along the north-south direction and finally coalesced into an inverse S-shaped filament. Consistent with the dextral chirality of the filament, magnetic helicity calculations show that an amount of negative helicity was persistently injected from the rotational positive magnetic element and accumulated during the formation of the filament. These observations suggest that twisted emerging fields may lead to the formation of the filament via reconnection with pre-existing fields and release of its inner magnetic twist. The persistent PRM might trace a covert twist relaxation from below photosphere to the low corona.
... Pariat et al. (2005) proposed to use a proxy GΦ(x), which meaningfully measures the connectivity-based helicity flux density per elementary magnetic flux tube. The method has been implemented by Dalmasse et al. (2014) and applied to observations by Dalmasse et al. (2013). Valori et al. (2012) implemented a finite volume method using the DeVore gauge and applied it to the force-free Titov-Démoulin model. ...
... Tziotziou et al. (2013) applied the connectivity-based method to a time series of 600 vector magnetic fields in active region 11158 and found that both the free magnetic energy and relative magnetic helicity are accumulated to sufficient amounts to power a series of solar eruptions. Dalmasse et al. (2013) first applied a connectivity-based helicity flux density to vector magnetic fields observed by SDO/HMI in active region 11158, and confirmed that the helicity flux density is mixed with both positive and negative signs. Liu et al. (2014) used the helicity flux integration method to study the helicity injection in emerging active regions. ...
The topology and dynamics of the three-dimensional magnetic field in the solar atmosphere govern various solar eruptive phenomena and activities, such as flares, coronal mass ejections, and filaments/prominences. We have to observe and model the vector magnetic field to understand the structures and physical mechanisms of these solar activities. Vector magnetic fields on the photosphere are routinely observed via the polarized light, and inferred with the inversion of Stokes profiles. To analyze these vector magnetic fields, we need first to remove the 180° ambiguity of the transverse components and correct the projection effect. Then, the vector magnetic field can be served as the boundary conditions for a force-free field modeling after a proper preprocessing. The photospheric velocity field can also be derived from a time sequence of vector magnetic fields. Three-dimensional magnetic field could be derived and studied with theoretical force-free field models, numerical nonlinear force-free field models, magnetohydrostatic models, and magnetohydrodynamic models. Magnetic energy can be computed with three-dimensional magnetic field models or a time series of vector magnetic field. The magnetic topology is analyzed by pinpointing the positions of magnetic null points, bald patches, and quasi-separatrix layers. As a well conserved physical quantity, magnetic helicity can be computed with various methods, such as the finite volume method, discrete flux tube method, and helicity flux integration method. This quantity serves as a promising parameter characterizing the activity level of solar active regions.
... The red line shows GOES flux.11158 is a notable active region observed by HMI. A series of papers have focused on the development of magnetic fields and solar flare-CMEs in active region NOAA 11158 based on observational vector magnetograms and EUV images (cf.Aschwanden et al., 2014;Bamba et al., 2013;Chintzoglou & Zhang, 2013;Dalmasse et al., 2013;Gary et al., 2014;Gosain, 2012;Guerra et al., 2015;Inoue et al., 2013;Jiang et al., 2012;Jing et al., 2012;Liu & Schuck, 2012;Malanushenko et al., 2014;Kazachenko et al., 2015;Petrie, 2012;Song et al., 2013;Su et al., 2012; ...
We present the photospheric energy density of magnetic fields in two solar active regions inferred from observational vector magnetograms, and compare it with the possible different defined energy parameters of magnetic fields in the photosphere. We analyze the magnetic fields in active region NOAA 6580-6619-6659 and 11158. It is noticed that the quantity 1/4pi Bn.Bp is an important energy parameter that reflects the contribution of magnetic shear on the difference between the potential magnetic field (Bp) and non-potential one (Bn), and also the contribution to the free magnetic energy near the magnetic neutral lines in the active regions. It is found that the photospheric mean magnetic energy density changes obviously before the powerful solar flares in the active region NOAA 11158, it is consistent with the change of magnetic fields in the lower atmosphere with flares.
