Abstract
Two intense magnetic clouds interacted with the same corotating high-speed solar wind stream in two successive rotations in the fall of 1978. In the August 27 event, the cloud was overtaken by the stream, the front half of the cloud still retained the basic properties of a simple intense cloud while the back half was the interaction region with a two-step velocity profile. In the September 25 event, the cloud was overtaking the same stream, its front half was now the interaction region while the back half had a rather more complex structure than a simple, non-interacting cloud. In the second event, the bulk velocity reached a very high peak value more than 900 km/s in the interaction region, and the Alfvénic speed in the cloud body also reached a high value of more than 600 km/s, which was the local solar wind speed. These two events show further the importance of an enhancement of the Al fvénic speed in accelerating the cloud. The properties of the geomagnetic storm and cosmic ray decrease caused by the clouds are also briefly discussed with reference to the Kp category of geomagnetic storms proposed by the author.
Published Version
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