MHD SIMULATION OF AN INTERACTION OF A SHOCK-WAVE WITH A MAGNETIC CLOUD

Interplanetary shock waves, propagating in the heliosphere faster than earlier-emitted coronal ejecta, penetrate them and modify their param eters during this interaction. Using two and one half dimensional MHD simulations, we show how a magnetic cloud ( flux rope) propagating wit h a speed 3 times higher than the ambient solar wind is affected by an even faster traveling shock wave overtaking the cloud. The magnetic f ield increases inside the cloud during the interaction as it is compre ssed in the radial direction and becomes very oblate. The cloud is als o accelerated and moves faster, as a whole, while both shocks (driven by the cloud and the faster interplanetary shock) merge upstream of th e cloud. This interaction may be a rather common phenomenon due to the frequency of coronal mass ejections and occurrence of shock waves dur ing periods of high solar activity.