A statistical study of magnetic cloud parameters and geoeffectiveness

Abstract

A statistical study of magnetic cloud parameters and geoeffectiveness is presented in this work, based on the analysis of 149 magnetic clouds during the period 1966–2001. The distributions of maximum magnetic field strength, solar wind speed and southward magnetic field inside the clouds were determined for the whole data set and for subsets classified according to the magnetic cloud polarity (rotation in Z or Y directions). The geoeffectiveness was determined by classifying the number of magnetic clouds followed by intense, moderate and weak magnetic storms, and by calm periods. It was found that around 77% of the magnetic clouds are geoeffective, i.e., they were followed by intense or moderate geomagnetic storms ( Dst ⩽ - 50 nT ) . Considering also weak storms ( Dst ⩽ - 30 nT ) , 97% of MCs were followed by geomagnetic activity. When considering polarity, each magnetic cloud subset has a slightly different geoeffectiveness, which is in agreement with the differences observed in their parameter distributions. The NSY - was observed to be the less geoeffective of the MC subsets, with 66.6% of this class events being followed by intense or moderate storms, against 73.0% of SNY + , 80.0% of the Y, 83.3% of the NSY - and 85.7% of the SNY - . The B peak – V peak relation was confirmed for the magnetic clouds with rotation in Z direction.