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In order to understand the interaction between MHD shocks and a cloud, a set of two-dimensional simulations for the interaction has been implemented. The computer code used is based on an approximate Riemann solver and an operator splitting method. The Riemann solver is constructed from conservation laws and includes all the discontinuities in the ideal MHD situation.
The initial condition is as follows. A MHD fast shock with Mach numbers 2, 5, 10, 20 and 50 is used as an incident shock in the interaction. The cloud is modeled as a cylinder. Both the cylinder and the tangential part of the magnetic field are perpendicular to the simulation domain. The cylinder has a circular cross-section. The magnetic field and thermal pressure roughly equally participate the total pressure in the unshocked gas. The normal and tangential parts of the magnetic field have the same magnitude. The state inside the cloud is assumed to be the same as its surroundings except for its mass density. The mass density contrasts between the cloud and its surroundings are set to 2:1, 5:1, 10:1, 20:1 and 40:1 for different models of the cloud.
In this paper, A fairly detailed picture for the interaction has been provided. It is observed from the simulations that the drag-length, which is the distance from the front of the undisturbed incident shock to the back face of the cloud when the incident shock wraps completely around the cloud, depends little on the Mach number of the incident shock for the given pre-shock state and a given cloud. The denser the cloud is, the larger is the drag-length. We also observed that the wrap-time, which is the duration from the impact of the incident shock on the front of the cloud to the completely wrapping of the cloud by the incident shock, depends little on the the density contrast for the given incident shock, but depends on the Mach number of the incident shock, and that the wrap-time divided by the Mach number of the incident shock ia approximately a constant for the given pre-shock state.
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