A STUDY OF GEOMAGNETIC STORMS AND ASSOCIATED SOLAR FLARES
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 45rı − 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.