Budget of energetic electrons during solar flares in the framework of magnetic reconnection

Mann, G.; Warmuth, A.

doi:10.1051/0004-6361/201014389

Cited by 20 publications

(25 citation statements)

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“…The role of small scale structures due to turbulence of the CS in particle acceleration has recently studied by Nishizuka and Shibata (2013) who found that the interaction of these structures provides an approach to Fermi acceleration for particles. Mann and Warmuth (2011) pointed out that, in a medium class flare, if about 8 % of the all electrons brought into CS by reconnection inflow are accelerated, they are able to bring about 12 % of the total released energy into the flare region; in a major flare, on the other hand, up 60 % total inflow electrons need to be accelerated to the energy > 20 keV to account for 60 % the total released energy observed in the flare region. In both cases, they found that the slow-mode shock plays a role in heating and the termination shock plays a role in particle accelerations.…”

Section: Discussionmentioning

confidence: 99%

Review on Current Sheets in CME Development: Theories and Observations

et al. 2015

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We introduce how the catastrophe model for solar eruptions predicted the formation and development of the long current sheet (CS) and how the observations were used to recognize the CS at the place where the CS is presumably located. Then, we discuss the direct measurement of the CS region thickness by studying the brightness distribution of the CS region at different wavelengths. The thickness ranges from 10 4 km to about 10 5 km at heights between 0.27 and 1.16 R from the solar surface. But the traditional theory indicates that the CS is as thin as the proton Larmor radius, which is of order tens of meters in the corona. We look into the huge difference in the thickness between observations and theoretical expectations. The possible impacts that affect measurements and results are studied, and physical causes leading to a thick CS region in which reconnection can still occur at a reasonably fast rate are analyzed. Studies in both theories and observations suggest that the difference between the true value and the apparent value of the CS thickness is not significant as long as the CS could be recognised in observations. We review observations that show complex structures and flows inside the CS region and present recent numerical modelling results on some aspects of these structures. Both observations and numerical experiments indicate that the downward reconnection outflows are usually slower than the upward ones in the same eruptive event. Numerical simulations show that the complex structure inside CS and its temporal behavior as a result of turbulence and the Petschek-type slow-mode shock could probably account for the thick CS and fast reconnection. But whether the CS itself is that thick still remains unknown since, for the time being, we cannot measure the electric current directly in that region. We also review the most recent laboratory experiments of reconnection driven by energetic laser beams, and discuss some important topics for future works.

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Section: Discussionmentioning

confidence: 99%

Review on Current Sheets in CME Development: Theories and Observations

et al. 2015

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“…Saint-Hilaire and Benz, 2005;Mann and Warmuth, 2011;Ryan et al, 2012). 7 This implies that coronal waves represent a non-negligible fraction of the energy released in a solar eruptive event (at least in smaller events).…”

Section: Energeticsmentioning

confidence: 99%

Large-scale Globally Propagating Coronal Waves

Warmuth

2015

Living Rev. Sol. Phys.

168

140

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Large-scale, globally propagating wave-like disturbances have been observed in the solar chromosphere and by inference in the corona since the 1960s. However, detailed analysis of these phenomena has only been conducted since the late 1990s. This was prompted by the availability of high-cadence coronal imaging data from numerous spaced-based instruments, which routinely show spectacular globally propagating bright fronts. Coronal waves, as these perturbations are usually referred to, have now been observed in a wide range of spectral channels, yielding a wealth of information. Many findings have supported the "classical" interpretation of the disturbances: fast-mode MHD waves or shocks that are propagating in the solar corona. However, observations that seemed inconsistent with this picture have stimulated the development of alternative models in which "pseudo waves" are generated by magnetic reconfiguration in the framework of an expanding coronal mass ejection. This has resulted in a vigorous debate on the physical nature of these disturbances. This review focuses on demonstrating how the numerous observational findings of the last one and a half decades can be used to constrain our models of large-scale coronal waves, and how a coherent physical understanding of these disturbances is finally emerging. Article RevisionsLiving Reviews supports two ways of keeping its articles up-to-date:Fast-track revision. A fast-track revision provides the author with the opportunity to add short notices of current research results, trends and developments, or important publications to the article. A fast-track revision is refereed by the responsible subject editor. If an article has undergone a fast-track revision, a summary of changes will be listed here.Major update. A major update will include substantial changes and additions and is subject to full external refereeing. It is published with a new publication number.For detailed documentation of an article's evolution, please refer to the history document of the article's online version at http://dx

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“…Many of these flares have already been used for comparison with the results of a shock-drift acceleration model (Mann et al 2009;Warmuth et al 2009b), and for the study of nonthermal energetics in the framework of magnetic reconnection (Mann & Warmuth 2011). Four different imaging methods were employed: CLEAN 3 , Pixon (Metcalf et al 1996), Visibiliy Forward Fit (Hurford et al 2005), and MEM_NJIT (Schmahl et al 2007).…”

Section: Observationsmentioning

confidence: 99%

Thermal and nonthermal hard X-ray source sizes in solar flares obtained from RHESSI observations

Warmuth

Mann

2013

A&A

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Context. A thorough understanding of solar flares requires determining the physical parameters of both the hot thermal plasma and the accelerated nonthermal electrons. This can be provided by hard X-ray (HXR) observations. In addition to HXR spectroscopy, imaging is needed to measure the geometric HXR source sizes. These parameters may vary as a function of flare size, importance, and time. Aims. We determine the scaling relations of the geometric source parameters of both thermal and nonthermal HXR sources with respect to length scale and flare importance, and we characterize their temporal evolution. This is required for further studies involving parameters such as thermal energies, plasma densities, and current densities. Methods. In a previous paper, we obtained time series of the geometric HXR source sizes (thermal and nonthermal) for 24 flares from GOES class C3.4 to X17.2 using the RHESSI instrument. Here, we investigate how themal volumes, nonthermal footpoint areas, and footpoint separations depend on the flare length scale and GOES importance. In addition,we study the time evolution of these geometric parameters.Results. The increase in the thermal source volume with length scale is slightly below a Euclidian scaling, but not too far from it. The thermal source volume is correlated with GOES class, which contrasts with what was found for RHESSI microflares. The nonthermal footpoint areas, on the other hand, are not well-correlated with either length scale or GOES class. With regard to temporal evolution, the RHESSI thermal source volumes tend to show a more complex behavior than the simple growth-decline pattern typical of flares observed in EUV. In most events, the thermal volume shows a rapid initial rise to a peak in the early impulsive phase. This peak is correlated with the initial downward motion of the coronal source, and is consistent with the notion of initially contracting magnetic field lines. Conclusions. The behavior of the geometric parameters of thermal and nonthermal HXR sources is generally consistent with the standard model of eruptive solar flares: a quasi-Euclidian scaling of volume with length scale, an initially decreasing thermal volume due to field line shrinking, followed by an increase in both volume and footpoint separation with time as the arcade of reconnected flare loops grows. However, the thermal volume is not the dominant factor in determining thermal energy, as well as thermal SXR and HXR flux. Electron density and/or temperature seem to be more important parameters in this respect.

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Budget of energetic electrons during solar flares in the framework of magnetic reconnection

Cited by 20 publications

References 53 publications

Review on Current Sheets in CME Development: Theories and Observations

Review on Current Sheets in CME Development: Theories and Observations

Large-scale Globally Propagating Coronal Waves

Thermal and nonthermal hard X-ray source sizes in solar flares obtained from RHESSI observations

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