  We present results from the first three-dimensional numerical simulations of
moderately supersonic cloud motion through a tenuous, magnetized medium. We
show that the interaction of the cloud with a magnetic field perpendicular to
its motion has a great dynamical impact on the development of instabilities at
the cloud surface. Even for initially spherical clouds, magnetic field lines
become trapped in surface deformations and undergo stretching. The consequent
field amplification that occurs there and particularly its variation across the
cloud face then dramatically enhance the growth rate of Rayleigh-Taylor
unstable modes, hastening the cloud disruption.
