A Study Of Geomagnetic Storms And Associated Solar Flares

ABSTRACT

Geomagnetic storms are temporal disturbances of the Earth’s magnetosphere caused by a

prolonged southward interplanetary magnetic field and usually coinciding with the arrival of

coronal mass ejections (CME). Most geomagnetic storms occur under disturbed condition

making it intrinsically uneasy to distinguish one geomagnetic storm from another especially in

respect of the solar origin. Thirty four (34) geomagnetic storms occurring between 1997-2012

have been studied whose storm signatures could be uniquely associated with the occurrence of

solar flare. Twelve (12) of this events are associated with flares that occurred within 45ı of the

central meridian (CM) while Eleven (11) were non- central meridian (NCM) solar flares. A weak

correlation (-0.24) was obtained between peak Dst and peak x-ray flux for all the thirty four (34)

events. When the CM flares were considered a strong correlation (-0.76) was obtained. The

correlation for NCM flares (between 45ı − 90ı) of the central meridian was much weaker than

the CM flares associated with geomagnetic storms. This result suggests that the solar flares

farther away from the central meridian are likely associated with major storms irrespective of the

size of the flare. These results have important implications for the present effort to predict the

occurrence of geomagnetic storms.