Study of geomagnetic storms with Dst < -100 nT during 1999 – 2002

Abstract

Ninety geomagnetic storms (GMSs) of intense nature, i.e. with Dst <-100 nT have been noticed using solar geophysical and interplanetary data during solar cycle 23. Out of which, 36 GMSs of intense (-200 nT ≤ Dst < -100 nT) nature and 10 of super intense (Dst < -200 nT) nature have occurred during the maximum phase, i.e. from 1999 to 2002, of solar cycle 23. The variation in time delay between the commencement and peak time of GMS is observed to be 5.5 to 42.5 h for different storms. The strength of GMS does not reveal any dependence with the duration of the storm as well as with the number of CMEs involved in the occurrence of storm. The high speed solar wind plasma, may be in the form of CMEs or else, is more likely to cause the intense and super intense GMSs. The solar features, i.e. X-ray solar flares (SFs), active prominences and disappearing filaments (APDFs), coronal mass ejections (CMEs), etc. responsible for causing GMSs have been studied. The geo-effective CMEs show longitudinal as well as hemispherical bias. Geo-effective CMEs causing intense and super intense GMSs are mostly confined between ±30° latitude and ±40° longitude. The correlation coefficients of 0.71 and 0.66, respectively of Bz and Vsw.Bz with Dst index indicates that Bz and Vsw.Bz may be considered as key contributors in determining the strength of GMSs.