Magnetic clouds observed in interplanetary space are probably the inte
rplanetary manifestations of coronal mass ejections. A looplike magnet
ic cloud is modeled as a gigantic flux rope that moves through the mag
netized medium of the solar wind. The dynamics of a model cylindrical
magnetic cloud is used to elucidate the motion of magnetic clouds and
their expansion in interplanetary space. Previous models of magnetic c
louds with the assumption of either force-free magnetic field or magne
tohydrostatic equilibrium preclude the consideration of motion. The dy
namical model, based on flux rope dynamics, allows the inclusion of fo
rces that drive the motion of the magnetic clouds relative to the sola
r wind.