Alfvén waves in solar flares

Abstract

Solar flares are dramatic events in which magnetic reconnection in the corona leads to heating of plasma to tens of MK and acceleration of particles to high energies. They also centrally involve transport between the corona (where the magnetic reconnection occurs) and the lower solar atmosphere (where most energy is radiated from). There is substantial evidence for the presence of Alfvénic waves/turbulence in solar flares, for example, in the ubiquitous nonthermal broadening of flare spectral lines. The physical role that Alfvénic waves have in the flare has attracted considerable attention, especially since 2007–2010. This article reviews what spectroscopic observations reveal about the properties and importance of Alfvénic waves, turbulence and transport in solar flares; mechanisms for wave excitation by magnetic reconnection at high Lundquist numbers and braking of the sunward reconnection jet; and models of wave energy transport to the lower atmosphere and the resulting heating and dynamics. The article finishes with discussion of the outlook for new progress.