We report here that near noon in the magnetosphere of Jupiter, plasma is observed to flow away from the equatorial current sheet. The motion reverses near dusk, with a subsequent infall of plasma towards the sheet on the nightside. We associate this motion with the compression of magnetic flux tubes on the dayside and their subsequent expansion on the nightside due to the solar wind interaction with Jupiter. Such compression and expansion may be sufficiently rapid that the plasma in the sheet cannot reach quasi-static equilibrium. Dynamic motions at transonic velocities ensue.