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Register a new userSpatio-temporal energy partitioning in a non-thermally dominated two-loop solar flare
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Solar flares show remarkable variety of the energy partitioning between thermal and nonthermal components. Those with a prominent nonthermal component but only a modest thermal one are particularly well suited to study the direct effect of the nonthermal electrons on plasma heating. Here, we analyze such a well observed, impulsive single-spike nonthermal event, a SOL2013-11-05T035054 solar flare, where the plasma heating can be entirely attributed to the energy losses of these impulsively accelerated electrons. Evolution of the energy budget of thermal and nonthermal components during the flare is analysed using X-ray, microwave, and EUV observations and three-dimensional modeling. The results suggest that (i) the flare geometry is consistent with a two-loop morphology and the magnetic energy is likely released due to interaction between these two loops; (ii) the released magnetic energy converted to the nonthermal energy of accelerated electrons only, which is subsequently converted to the thermal energy of the plasma; (iii) the energy is partitioned in these two flaring loops in comparable amounts; (iv) one of these flaring loops remained relatively tenuous but rather hot, while the other remained relatively cool but denser than the first one. Therefore, this solar flare demonstrates an extreme efficiency of conversion of the free magnetic energy to the nonthermal energy of particle acceleration and the energy flow into two loops from the non-thermal to thermal one with a negligible direct heating.
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The energy released in solar flares derives from a reconfiguration of magnetic fields to a lower energy state, and is manifested in several forms, including bulk kinetic energy of the coronal mass ejection, acceleration of electrons and ions, and enhanced thermal energy that is ultimately radiated away across the electromagnetic spectrum from optical to X-rays. Using an unprecedented set of coordinated observations, from a suite of instruments, we here report on a hitherto largely overlooked energy component -- the kinetic energy associated with small-scale turbulent mass motions. We show that the spatial location of, and timing of the peak in, turbulent kinetic energy together provide persuasive evidence that turbulent energy may play a key role in the transfer of energy in solar flares. Although the kinetic energy of turbulent motions accounts, at any given time, for only $sim (0.5-1)$% of the energy released, its relatively rapid ($sim$$1-10$~s) energization and dissipation causes the associated throughput of energy (i.e., power) to rival that of major components of the released energy in solar flares, and thus presumably in other astrophysical acceleration sites.
Plasma turbulence is thought to be associated with various physical processes involved in solar flares, including magnetic reconnection, particle acceleration and transport. Using Ramaty High Energy Solar Spectroscopic Imager ({it RHESSI}) observations and the X-ray visibility analysis, we determine the spatial and spectral distributions of energetic electrons for a flare (GOES M3.7 class, April 14, 2002 23$:$55 UT), which was previously found to be consistent with a reconnection scenario. It is demonstrated that because of the high density plasma in the loop, electrons have to be continuously accelerated about the loop apex of length $sim 2times 10^9$cm and width $sim 7times 10^8$cm. Energy dependent transport of tens of keV electrons is observed to occur both along and across the guiding magnetic field of the loop. We show that the cross-field transport is consistent with the presence of magnetic turbulence in the loop, where electrons are accelerated, and estimate the magnitude of the field line diffusion coefficient for different phases of the flare. The energy density of magnetic fluctuations is calculated for given magnetic field correlation lengths and is larger than the energy density of the non-thermal electrons. The level of magnetic fluctuations peaks when the largest number of electrons is accelerated and is below detectability or absent at the decay phase. These hard X-ray observations provide the first observational evidence that magnetic turbulence governs the evolution of energetic electrons in a dense flaring loop and is suggestive of their turbulent acceleration.
Solar flares are a fundamental component of solar eruptive events (SEEs; along with solar energetic particles, SEPs, and coronal mass ejections, CMEs). Flares are the first component of the SEE to impact our atmosphere, which can set the stage for the arrival of the associated SEPs and CME. Magnetic reconnection drives SEEs by restructuring the solar coronal magnetic field, liberating a tremendous amount of energy which is partitioned into various physical manifestations: particle acceleration, mass and magnetic-field eruption, atmospheric heating, and the subsequent emission of radiation as solar flares. To explain and ultimately predict these geoeffective events, the heliophysics community requires a comprehensive understanding of the processes that transform and distribute stored magnetic energy into other forms, including the broadband radiative enhancement that characterises flares. This white paper, submitted to the Heliophysics 2050 Workshop, discusses the flare impulsive phase part of SEEs, setting out the questions that need addressing via a combination of theoretical, modelling, and observational research. In short, by 2050 we must determine the mechanisms of particle acceleration and propagation, and must push beyond the paradigm of energy transport via nonthermal electron beams, to also account for accelerated protons & ions and downward directed Alfven waves.
Solar flares are a fundamental component of solar eruptive events (SEEs; along with solar energetic particles, SEPs, and coronal mass ejections, CMEs). Flares are the first component of the SEE to impact our atmosphere, which can set the stage for the arrival of the associated SEPs and CME. Magnetic reconnection drives SEEs by restructuring the solar coronal magnetic field, liberating a tremendous amount of energy which is partitioned into various physical manifestations: particle acceleration, mass and magnetic-field eruption, atmospheric heating, and the subsequent emission of radiation as solar flares. To explain and ultimately predict these geoeffective events, the heliophysics community requires a comprehensive understanding of the processes that transform and distribute stored magnetic energy into other forms, including the broadband radiative enhancement that characterises flares. This white paper, submitted to the Heliophysics 2050 Workshop, discusses the flare gradual phase part of SEEs, setting out the questions that need addressing via a combination of theoretical, modelling, and observational research. In short, the flare gradual phase persists much longer than predicted so, by 2050, we must identify the characteristics of the significant energy deposition sustaining the gradual phase, and address the fundamental processes of turbulence and non-local heat flux.
Non-potential magnetic energy promptly released in solar flares is converted to other forms of energy. This may include nonthermal energy of flare-accelerated particles, thermal energy of heated flaring plasma, and kinetic energy of eruptions, jets, up/down flows, and stochastic (turbulent) plasma motions. The processes or parameters governing partitioning of the released energy between these components is an open question. How these components are distributed between distinct flaring loops and what controls these spatial distributions is also unclear. Here, based on multi-wavelength data and 3D modeling, we quantify the energy partitioning and spatial distribution in the well observed SOL2014-02-16T064620 solar flare of class C1.5. Nonthermal emissions of this flare displayed a simple impulsive single-spike light curves lasting about 20,s. In contrast, the thermal emission demonstrated at least three distinct heating episodes, only one of which was associated with the nonthermal component. The flare was accompanied by up and down flows and substantial turbulent velocities. The results of our analysis suggest that (i) the flare occurs in a multi-loop system that included at least three distinct flux tubes; (ii) the released magnetic energy is divided unevenly between the thermal and nonthermal components in these loops; (iii) only one of these three flaring loops contains an energetically important amount of nonthermal electrons, while two other loops remain thermal; (iv) the amounts of direct plasma heating and that due to nonthermal electron loss are comparable; (v) the kinetic energy in the flare footpoints constitute only a minor fraction compared with the thermal and nonthermal energies.
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