Relation between coronal mass ejections, solar flares, certain parameters of the magnetosphere, and different auroras during great magnetic storms

Seven great magnetic storms, during which the minimal values of the Dst variation were lower than -250 nT (on February 10-11, 1958; February 8-9, 1986; March 13-14, 1989; October 21-22, 1989; March 24-25, 1991; October 28-29, 1991; and November 8-9, 1991), have been analyzed. All these superstorms followed solar flares and, sometimes, coronal mass ejections. Bright auroras, whose spectra depended on the type of a heliospheric source responsible for the origination of a specific storm and for the properties of the upper atmosphere, were recorded in wide regions of the Earth during these superstorms. Bright green and red type A auroras were observed in particular cases. Certain assumptions have been made on the origin and mechanisms of generation of similar aurora types. Information about the parameters of the solar wind that generates these storms is either absent or extremely scanty. Data on a convection potential during storms are also sparse. Therefore, the electric potential drop across the polar cap has been estimated based on the time variations in Dst. The high values of these parameters have been obtained, which agrees with results of some experiments.