Abstract:
A set of 50 intense geomagnetic storms follows the criteria of Dst≤-100 nT, IMF B ≥10 nT with time duration ≥ 3 hr., during the solar maximum period (1989-91) of solar cycle 22 have been analysed. The study of this short period 1989-91 has a unique importance because the maximum phase of solar cycle 22 containing large time duration 3 yr and two solar peaks, during the year 1989 and 1991 are exceptional among other previous 21 solar cycles. Recent work demonstrated some important characteristics and different solar and interplanetary associations of 50 selected storm events, which are mentioned in Table 1. Out of 50 storm events, it is found that maximum numbers of intense geomagnetic storms are associated with transient disturbances in solar wind streams, which causes strong interplanetary shocks in interplanetary medium, whereas, a few numbers of intense geomagnetic storms are associated with corotating flows in solar wind streams. We have described two intense geomagnetic storm events associated with corotating flows and transient disturbances respectively and concluded that kind of solar wind does not effect the general characteristics and variation trends of different phases of storms. The association of supersonic shocks and magnetic clouds with intense geomagnetic storms have also been discussed.
