Abstract:
The effect of solar features on geospheric conditions leading to ninety
nine geomagnetic storms (OMSs) with H~400 nT and Ap;::;:20 have been investigated
using interplanetary magnetic field (IMF) , solar wind plasma (SWP) and solar
geophysical data (SGD) during the period 1979-99. Ha, X-ray solar flares occured
within lower latitudinal zone i.e., 30"N-O-30oS, are associated with maximum number
of GMSs. Further, 91.7% of total APDFs occured within helio-Iatitudinal range
30oN-O-30oS are associated with GMSs. No significant correlation between magnitude
(intensity) of OMS and importance of Ha. X-ray solar flares is observed. Magnitude
of GMSs is associated with different properties ofHa, X-ray solar flares and APDFs
i.e, NOAA region, location (heiio-longitudeJlatitude), duration and area of solar
events. It is observed statistically that 77.2%, 62.8% and 68.5% GMSs are associated
with Ha' X-ray solar flares and APDFs respectively. It is observed that coronal mass
ejection (CMEs) related storm sudden commencements (SSCs) are not always
associated with high speed solar wind streams (HSSWS). Associated solar activity
of CME events near the Sun are eruptive prominences, long duration solar events,
impulsive X-ray events, optical flares, type II and IV radio burst leading to SSCs.
The travel time between the explosion on the solar disc and maximum geomagnetic
activity has been observed in the range 53-114 Hrs.
