Characteristic features of ICMEs associated with big storms in geomagnetic activity and large Forbush decreases in cosmic ray intensity

265-269The solar sources and features of interplanetary structures associated with big geomagnetic storm (GS) and/or large Forbush decrease (FD) events have been investigated. The hourly data of geomagnetic activity, cosmic ray (CR) intensity, and solar wind plasma/field has been utilized during the passage of ICMEs and associated structures (e.g. shock/seath, interaction region/high speed stream). The geo-effectiveness and CR-effectiveness of ICMEs, similarities and distinctions between them together with variations/fluctuations in interplanetary plasma/field parameters is utilized in order to identify distinct feature(s) of ICMEs and physical mechanism(s) playing important role in the development of GS and FD