Solar wind and IMF parameters associated with geomagnetic storms with Dst <-50 nT

A correlative study between the intensity of a geomagnetic storm (given by the Dst index) and the peak value reached by some solar wind parameters (velocity and density) and the southward component of the interplanetary magnetic field (IMF) is made. This study has been performed by using hourly values of the Dst index and measurements taken by the ACE spacecraft in the period 2000-2005, for which 72 geomagnetic storms were considered. It is confirmed that peak Dst is correlated to the maximum negative component B-z of the IMF better than the maxima of n and V (solar wind number density and speed, respectively). By considering all the storms, the correlation coefficient was found to be 0.88. If we consider the geomagnetic storms for which -200 nT < peak Dst < -60 nT, a lower correlation coefficient of 0.63 is obtained.