Solar flare associated coronal mass ejections causing geo-effectiveness and Forbush decreases

Abstract

In the present study, we have selected 35 halo Coronal Mass Ejections (CMEs) associated with solar flares, Geomagnetic Storms (GSs) and Forbush decrease (Fd) chosen from 1st January 2000 to 31st December 2007 (i.e., the descending phase of solar cycle 23) observed by the Large Angle Spectrometric Coronagraph (LASCO) on board the SOHO spacecraft. Statistical analyses are performed to look at the distribution of solar flares associated with halo CMEs causing GSs and Fd and investigated the relationship between solar flare and halo CME parameters with GSs and Fd. Forbush decrease is the phenomenon of rapid decrease in cosmic ray intensity following the CME. Our analysis indicates that during 2000 to 2007 the northern region produced 44 % of solar flares associated with halo CMEs, GSs, and Fd, whereas 56 % solar flares associated with halo CMEs, GSs, and Fd were produced in the southern region. The northern and the southern hemispheres between 10° to 20° latitudinal belts are found to be more effective in producing events leading to Fd. From our selected events, we found that about 60 % of super-intense storms (\(\mbox{Dst} \leq -200~\mbox{nT}\)) caused by halo CMEs are associated with X-class flares. Fast halo CMEs associated with X-class flares originating from 0° to 25° latitudes are better potential candidates in producing super-intense GSs than the slow halo CMEs associated with other classes of flares.