Statistic study of the geoeffectiveness of compression regions CIRs and Sheaths

We statistically study the geoeffectiveness of two types of compression regions: corotating interaction regions (CIRs) before the solar wind high-speed streams (HSSs) from the coronal holes and Sheaths before the fast interplanetary CMEs (ICMEs) including flux-rope magnetic clouds (MCs) and non-MC Ejecta using the OMNI dataset (http://omniweb.gsfc.nasa.gov (King and Papitashvili, 2004)) and our Catalog of large-scale solar wind phenomena for 1976-2000 (ftp://ftp.iki.rssi.ru/pub/omni/(Yermolaev et al., 2009)). Our analysis shows that the magnitude of the interplanetary magnetic field B in CIRs and Sheaths increases with increasing speed of both types of pistons: HSS and ICME; the increase of the piston speed results in the increase of geoeffectiveness of both compression regions. The value B in Sheaths before Ejecta is higher than B in Ejecta. The value B in Sheaths before MCs in the beginning of phenomena interval is lower than in MCs but in the end of interval it is close to B in MCs. The contribution of Sheath in storm generation can be significant for so-called "CME-induced" storms and Sheath-induced storms should be identified and analyzed separately.