Interplanetary conditions for CIR-induced and MC-induced geomagnetic storms

We present a comparison of conditions in the interplanetary space during geomag-netic storms which are generated by 2 types of large-scale interplanetary phenom-ena- corotating interaction region (CIR) and magnetic cloud (MC or interplanetary coronal mass ejection, ICME). We select also 2 geoeffective parts of MC- compressed region ahead of leading edge of MC (Sheath) and the body of MC. Superposed epoch analyses of interplanetary parameters during 1976-2000 are used separately (1) for 2 epoch zero times: start and end of main phase of geomagnetic storms and (2) for 4 categories of solar wind: CIR (121 storms), Sheath (22), MC (113), and ”un-certain”(367). Though the greatest southward IMF component is observed, on the average, in magnetic clouds, the strongest storms are generated by Sheath (but not body of MC). In spite of large differences of parameters in various types of solar wind, the turning of IMF exerts primary control over start and end of a magnetic storm