Three-dimensional Magnetohydrodynamic Numerical Simulations of Cloud-Wind Interactions

We present results from three-dimensional numerical simulations investigating the magnetohydrodynamics of cloud-wind interactions. The initial cloud is spherical, while the magnetic field is uniform and transverse to the cloud motion. A simplified analytical model that describes the magnetic energy evolution in front of the cloud is developed and compared with simulation results. In addition, it is found that the interaction of the cloud with a magnetized interstellar medium results in the formation of a highly structured magnetotail. The magnetic flux in the wake of the cloud organizes into flux ropes, and a reconnection current sheet is developed as field lines of opposite 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 an important dynamical effect on the subsequent evolution of the cloud, since some unstable modes tend to be strongly enhanced.