Flare Observations

Abstract

Solar flares are observed at all wavelengths from decameter radio waves to gamma-rays at 100 MeV. This review focuses on recent observations in EUV, soft and hard X-rays, white light, and radio waves. Space missions such as RHESSI, Yohkoh, TRACE, and SOHO have enlarged widely the observational base. They have revealed a number of surprises: Coronal sources appear before the hard X-ray emission in chromospheric footpoints, major flare acceleration sites appear to be independent of coronal mass ejections (CMEs), electrons, and ions may be accelerated at different sites, there are at least 3 different magnetic topologies, and basic characteristics vary from small to large flares. Recent progress also includes improved insights into the flare energy partition, on the location(s) of energy release, tests of energy release scenarios and particle acceleration. The interplay of observations with theory is important to deduce the geometry and to disentangle the various processes involved. There is increasing evidence supporting reconnection of magnetic field lines as the basic cause. While this process has become generally accepted as the trigger, it is still controversial how it converts a considerable fraction of the energy into non-thermal particles. Flare-like processes may be responsible for large-scale restructuring of the magnetic field in the corona as well as for its heating. Large flares influence interplanetary space and substantially affect the Earth’s lower ionosphere. While flare scenarios have slowly converged over the past decades, every new observation still reveals major unexpected results, demonstrating that solar flares, after 150 years since their discovery, remain a complex problem of astrophysics including major unsolved questions.Electronic Supplementary MaterialSupplementary material is available for this article at 10.12942/lrsp-2008-1.

Moreton and EUV Waves Associated with an X1.0 Flare and CME Ejection

“…CMEs and flares can be observed separately or in conjunction, and they are generally associated with large active regions (ARs) with a complex magnetic field structure. The influence of flares and CMEs on the solar atmosphere includes a wide ariety of phenomena, such as radio bursts, accelerated particle beams, formation of transient coronal holes, shocks, and large-scale propagating perturbations like Moreton and EUV waves among others (Benz, 2008;Chen, 2011;Webb and Howard, 2012).…”

Hαspectroscopy and multiwavelength imaging of a solar flare caused by filament eruption

“…More details about solar flares can be found in several reviews (e.g. Hudson 2007;Benz 2008;Shibata & Magara 2011;Fletcher et al 2011).…”

Horizontal flow fields observed in Hinode G-band images

“…In addition to modeling efforts, a wealth of new data became available by space missions such as RHESSI, Yohkoh, TRACE, and SoHO. Observations in the extreme ultraviolet (EUV) and in soft/hard X-rays revealed a plethora of transition region and coronal arcades and loops as summarized by Benz (2008), who discusses energetic and eruptive events as well as the nature of energy release and particle deposition. More recently, the relevant MHD processes such as flux emergence, formation of a current sheet, rapid dissipation of electric current, shock heating, mass ejection, and particle acceleration have been recounted by Shibata & Magara (2011).…”