December 1, 2022

Energy budget of plasma motions, heating, and electron acceleration in a three-loop solar flare by G. Motorina et al.*

The solar flare phenomenon is a complex process in the solar atmosphere where non-potential magnetic energy is launched and converted into other forms of energy, such as nonthermal energy of sped up particles, thermal energy of heated flaring plasma, kinetic energy of eruptions, jets, up/down flows, and stochastic (turbulent) plasma motions. The procedures lying behind preliminary division between energy components, circulation of these parts among flaring loops and their development are not yet fully understood.
Here we quantify the energy partitioning and spatial circulation in a SOL2014-02-16T064620 solar flare of class C1.5, which has relatively weak thermal action comparable to cold flares. This occasion is an unusual case when a rather simple flare with a single-spike spontaneous stage was observed with IRIS so we can measure the kinetic energy of bulk and unstable plasma motions in the flare footpoints..
Analysis of Observations.
In the study we evaluate SDO/AIA and RHESSI information to take into consideration both hot and moderately heated elements of the flaring plasma in the coronal part of the flare. Using the regularized inversion code to the SDO/AIA information (Hannah & & Kontar 2012, 2013) and the method explained in Motorina et al. (2020) we calculate the spatial distribution of temperature level, emission procedure, and thermal energy density (Figure 1, a). The main contribution to the thermal energy comes from the flare area (box 2 in Figure 1, a, upper left panel) which can be divided into 2 areas (marked with green/magenta lines) corresponding to 2 various flaring loops. The bulk of the thermal energy included in the flare region is similarly divided in between these two loops (Figure 1, b). Evolution of this energy (from box 2) is revealed in Figure 1( c) in black with its peak value at ~ 7 × 1028 [erg]
To compute the thermal energy found by RHESSI, we utilize the emission measure and temperature gotten from the RHESSI fit and volume of the corresponding Loop II from a 3D flare design. These observations in conjunction with the NoRP, RSTN, and BBMS data in microwave range and a built 3D model of the flare are used to estimate the nonthermal energy deposition in the flare (Figure 1, c, blue line). The nonthermal energy deposition obtained from the RHESSI fit (Figure 1, c, dark blue rushed line) during the decay phase does not oppose any offered information.
The IRIS information show activity (impulsive improvements in the flare location) temporally coinciding with the spontaneous emission from Konus-Wind and microwaves. We examine the spectral lines Si IV, O IV, and Fe XXI which form at various transition region to coronal temperature levels. We fit a Gaussian function to each pixel for each spectral line to determine their Doppler velocities and Doppler widths and hence to quantify the kinetic energy of the plasma streams and unstable movements. Because of weak signatures of Fe XXI, we can not use this spectral line to approximate a coronal part of the kinetic energy. The considered temperature level variety 104.8-105.1 K belongs to the flare footpoints. Therefore, these information measure just a portion of the overall kinetic energy in the flare. We determine which IRIS pixels lie inside the 50% RHESSI 6-9 keV shape and determine this energy 3 × 1024 [erg] We discovered the overall turbulent kinetic energy for the same volume as less than 7 × 1025 [ erg]

Figure 1– (a) Spatial distributions of plasma specifications derived from SDO/AIA: temperature (top left panel), emission measure (leading ideal panel), chi-square (bottom left panel), thermal energy density (bottom right panel). The green and red signs show the design values of thermal energies Loops I and II, respectively.
3D Modeling.
Based on the NLFFF extrapolation code (Fleishman et al. 2017) initiated with an SDO/HMI vector magnetogram taken at 06:34:12 UT and GX Simulator (Nita et al. 2015) we developed a 3D flare design (Figure 2). The GX Simulator functionality allows computation (and visualisation) of chosen magnetic field lines such as to match readily available flare images.
Based on the only available microwave spectral data at 06:44:41 UT we discovered that energetically dominant portion of the nonthermal electrons must be located in Loop II. The constructed model is consistent with all readily available observational restraints and, hence, confirmed by the data.
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Figure 2– The 3D model with three flux tubes labeled with their numbers (I– III). (a) Magnetic flux tubes. (b) Distribution of thermal number density in the flux tubes. (c) Distribution of nonthermal number density in the flux tubes (in Loop II just). (d) Distribution of the temperature in the flux tubes.
Conclusions.
In this research study, we have evaluated the SOL2014-02-16T064600 flare which has three distinct successive heating episodes, where the second one looked like a response on the nonthermal impulsive peak. From the timing of the event, we can conclude that only a portion of the flaring plasma heating was driven by nonthermal electron losses, while the remaining part was driven by another agent.
The circulation of the energy elements over the 3 flaring loops involved in the event was extremely uneven. The accounted types of the kinetic energy in the flare footpoints made up only a small fraction compared with the nonthermal and thermal energies.
Nonthermal energy input sufficed for the postimpulsive heating in the flaring loop with nonthermal electrons, but inadequate for the total thermal reaction in the flare..
Based upon the recently released paper: Gregory D. Fleishman, Lucia Kleint, Galina G. Motorina, Gelu M. Nita, and Eduard P. Kontar, Energy spending plan of plasma movements, heating, and electron velocity in a three-loop solar flare, The Astrophysical Journal, 913, 97 (2021) (https://doi.org/10.3847/1538-4357/abf495).
Recommendations.
Hannah I.G. & & Kontar E.P. 2012, A&A, 539, A146 https://doi.org/10.1051/0004-6361/201117576 .
Hannah I.G. & & Kontar E.P. 2013, A&A, 553, A10 https://doi.org/10.1051/0004-6361/201219727 .
Lysenko A.L. et al. 2018, ApJ, 856, 111 https://doi.org/10.3847/1538-4357/aab271 .
Motorina G.G. et al, 2020, ApJ, 890, 75 https://doi.org/10.3847/1538-4357/ab67d1 .
Fleishman G.D. et al. 2017, ApJ, 839, 30 https://doi.org/10.3847/1538-4357/aa6840 .
Nita, G. M. et al. 2015, ApJ, 799, 236 https://doi.org/10.1088/0004-637X/799/2/236 .
* Full list of authors: Gregory D. Fleishman, Lucia Kleint, Galina G. Motorina, Gelu M. Nita, and Eduard P. Kontar.

The solar flare phenomenon is an intricate process in the solar environment where non-potential magnetic energy is released and transformed into other kinds of energy, such as nonthermal energy of accelerated particles, thermal energy of heated flaring plasma, kinetic energy of eruptions, jets, up/down circulations, and stochastic (unstable) plasma motions. The main contribution to the thermal energy comes from the flare area (box 2 in Figure 1, a, upper left panel) which can be divided into 2 regions (marked with green/magenta lines) corresponding to 2 various flaring loops. The bulk of the thermal energy consisted of in the flare area is equally divided between these two loops (Figure 1, b). These observations in combination with the NoRP, RSTN, and BBMS information in microwave range and a developed 3D design of the flare are used to approximate the nonthermal energy deposition in the flare (Figure 1, c, blue line). The accounted forms of the kinetic energy in the flare footpoints constituted only a small portion compared with the thermal and nonthermal energies.

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