Geomagnetic storms with H ≥ 400nT during 1979-99

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.