Three-dimensional magnetohydrodynamic numerical simulations of cloud-wind interactions

We present results from three-dimensional numerical simulations investigati ng the magnetohydrodynamics of cloud-wind interactions. The initial cloud i s spherical, while the magnetic held is uniform and transverse to the cloud motion. A simplified analytical model that describes the magnetic energy e volution in front of the cloud is developed and compared with simulation re sults. In addition, it is found that the interaction of the cloud with a ma gnetized interstellar medium results in the formation of a highly structure d magnetotail. The magnetic flux in the wake of the cloud organizes into fl ux ropes, and a reconnection current sheet is developed as field lines of o pposite polarity are brought close together near the symmetry axis. At the same time magnetic pressure is strongly enhanced at the leading edge of the cloud from the stretching of the field lines that occurs there. This has a n important dynamical effect on the subsequent evolution of the cloud, sinc e some unstable modes tend to be strongly enhanced.