High-Energy Aspects of Solar Flares: Recent Advances in Observations and Models

Solar flares are one of the most spectacular manifestations of solar activity with significant space-weather impacts. They also serve as a unique laboratory for probing the underlying physics of wide-ranging processes, including magnetic reconnection, generation of plasma turbulence and shocks, particle acceleration, and plasma heating. Solar flares thus bear important implications for physically similar phenomena elsewhere in the universe, such as laboratory plasmas, planetary magnetospheres, and flares on other stars or near compact objects. In this presentation, we review recent observational and modeling advances in solar flare research, with a focus on high-energy aspects. Special attention will be paid to imaging and spectroscopic observations, e.g., of long-duration and behind-the-limb gamma-ray flares detected by Fermi, of coronal reconnection sites seen by RHESSI, SDO, Hinode, and IRIS, and of the flaring lower atmosphere (chromosphere and transition region) seen by IRIS. We will discuss broad physical connections of flares to other phenomena on the Sun (to a much greater extent than conventionally thought), such as the correlation between quasi-periodic flare pulsations (seen from radio to hard X-rays) and various MHD waves (some are directly imaged). We will also review relevant modeling efforts to explain these observations, focusing on a hybrid model of stochastic (by turbulence) plus shock acceleration of particles, as well as combined kinetic and radiative hydrodynamic simulations.