Geoeffectiveness of corotating interaction regions as measured by Dst index

Corotating interaction regions (CIRs) are structures formed when high-speed solar wind streams overtake slow solar wind streams as they propagate outward. These structures produce regions of enhanced density and magnetic field strength in the solar wind near the ecliptic plane. In this paper, the geoeffectiveness of CIRs, as measured by the geomagnetic Dst index, is assessed during the solar wind observational period 1964-2003. A catalogue of CIRs is constructed by consulting high-speed plasma streams (HSPS) lists present in the literature and by analyzing solar wind parameters for each HSPS event. The geoeffectiveness of CIRs is analyzed by determining the number of intense (Dst <= -100 nT), moderate (-100 < Dst <= -50 nT), or weak (-50 < Dst <= -30 nT) magnetic storms that followed each CIR event. Statistical distributions of CIR parameters (maximum solar wind speed, maximum convection electric field, southward magnetic field peak) and geoeffectiveness (Dst peak) are obtained. Correlation analyses of Dst index with various solar wind parameters are presented. A comparison with the geoeffectiveness of other interplanetary structures such as shocks, magnetic clouds, and sector boundaries is performed. Our results show that 33% of CIRs are followed by moderate/intense magnetic activity (Ds t< -50 nT), i.e., approximately one third of the CIR events observed near Earth are geoeffective.