Statistical analysis of corotating interaction regions and their geoeffectiveness during solar cycle 23

This is an investigation of the effects of corotating interaction regions (CIRs) in the heliosphere (<1 AU) on geomagnetic disturbances during solar cycle 23 (1996-2005). Three kinds of interplanetary structures, "pure" CIR, interaction of CIR with ICME, and "pure" ICME by transient events, are identified by using the Hakamada-Akasofu-Fry (HAF) solar wind model. Yearly occurrence of 157 "pure" CIRs has a minimum value in 2001 and a peak value in 2003 at the declining phase during the 23rd solar cycle. The maximum correlation coefficient of the daily sum of Kp indices between consecutive Carrington Rotations indicates that recurrent geomagnetic disturbances are dominant during the declining phase near solar minimum. Eighty percent of storms that are related to "pure" CIRs belong to weak and moderate storms. The statistical analysis shows that about 50% of CIRs produce classical interplanetary shocks during the descending phase and 89% of the CIR-related shocks are followed by geomagnetic storms. These results demonstrate that CIR-related shock is not a necessary condition for generating a magnetic storm, but most CIR-related shocks are related to a storm. The Dst index that corresponds to CIR-related storms has a better linear relationship with IMF Bz, Ey, and the coupling function (ε) when the Dst indices are higher than -100 nT. Finally, the geoeffectiveness of CIRs appears clearly to have a seasonal variation.