Six typical geomagnetic storms are analyzed from the aspect of varieties of morphologycategories of magnetic storms with sudden commencement caused by interplanetary magneticclouds. The main conclusions obtained are drawn. The high-density structure in front ofmagnetic cloud is an important factor in determining the property of the initial phase ofgeomagnetic storm. Under similar conditions for the magnetic field of magnetic cloud, thevelocities of both the background solar wind and the magnetic cloud affect the developmentand intensity of magnetic storm. The onset and recovery of strong main phase are control-led by the orientation of the field vector inclination with respect to the ecliptic plane. Oneof the main features of the storm generated from a positive magnetic cloud is the long-delayed main phase. The solar wind streams behind the magnetic cloud keep affecting therecovery of main phase of magnetic storm.
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