Difference in the parameters of ICMEs in Ejecta and Sheath region and their impact on Dst index during 1997-2014

The comparisons in respect of mean parameters in ejecta and sheath region during 1997-2014 have been studied here. The results from statistical analysis indicate that all the parameters, are more powerful (in respect of amplitude) in the sheath region than that of ejecta, whether there is magnetic cloud (MC) structure or not. Probably, a shock plays the key role to such increases. The inter-relation of parameters in the sheath is higher than that of ejecta. In addition, I also discuss the nature of storm influence parameters variation in the sheath and ejecta separately for MC or non MC. The results in respect of t-test and correlations confirm that, associated with the shock, the magnetic field in the sheath region are opened up and sheath parameters are more energetic for producing geomagnetic storm. I have proposed multiple linear regression model for the prediction of response variable (Dst index) by using mean of the total magnetic field, southward magnetic field, velocity of the solar wind. About 61% of the observed value can be predicted using this model for MC. The correlation becomes strong in case of addition and multipliction functions from the dependent components of multiple regression line equation with Dst index than that of individual parameters of MC and non MC with Dst index. Thus it is preferable to investigate accomulated effect of ICMEs causing successive geomagnetic stroms as compaired to their isolated effects. One ultimate finding is that, there is a higher correlation between Dst index and solar wind parameters (individually or combined) in the sheath than the ones in the ejecta, for both MCs and non-MCs.