Magnetic clouds observed in interplanetary space are probably the interplanetary manifestations of coronal mass ejections. A looplike magnetic cloud is modeled as a gigantic flux rope that moves through the magnetized 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 clouds with the assumption of either force-free magnetic field or magnetohydrostatic equilibrium preclude the consideration of motion. The dynamical model, based on flux rope dynamics, allows the inclusion of forces that drive the motion of the magnetic clouds relative to the solar wind.
