Classification of solar flares

The historical background of solar flare classification before the SMM launch is reviewed along with recent developments made by observations with SMM, Hinotori, and other contemporary satellite and ground-based observations. Based on these recent findings, solar flares are grouped into five classes: thermal hard X-ray flares, nonthermal hard X-ray flares, impulsive gamma-ray/proton flares, gradual gamma-ray/proton flares, and quiescent filament-eruption flares. The roles of filament eruptions in flare development are examined, and theoretical ideas related to processes occurring in different flare classes are discussed.