Type a red auroras during superstorms, caused by coronal mass ejection (CMEs)

Two geomagnetic superstorms during the minimum activity phase of solar cycle 22 were chosen for the analysis of geophysical situation: October 21-22. 1989 (min Dst = -270 nT) and March 24-25, 1991 (min Dst = -298 nT). The first event is associated with the X13.0/4B flare accompanied by the coronal mass ejection (CME). The second storm might have been produced by a CME driven interplanetary shock presumably related to the X9.8/3B flare. On October 21, 1989 (15.00-18.00 UT) at Loparskaya observatory (Kola peninsula) red type A auroras were observed (maximum 630.0 nm intensity about 25 kR, maximum 557.7 nm intensity about 10 kR). During the main phase of the storm on March 24-25. 1991 instrumental and visual observations of auroras were carried out during the entire night at Loparskaya observatory. The intensity ratio 16300/1557.7 exceeded 1 and red type A auroras were observed from 20.00 until 22.00 UT and also at 23.30 and 01.00 UT. It has been found that this auroral emission with an extremely high intensity ratio of 630.0 nm to 557.7 nm was produced by low energy electron precipitation.