Anti‐solar acceleration of ionospheric plasma across the Venus terminator

We demonstrate that the horizontal ionospheric particle pressure gradient across the Venus terminator is the principal body force accelerating the plasm to the observed anti‐solar velocity. The large scale horizontal electromagnetic body force is typically an order of magnitude smaller than the particle pressure gradient. The viscous body forces above 300 km—drag or acceleration—are also an order of magnitude smaller than the pressure gradient body force. In the immediate vicinity of the ionopause where the ionospheric plasma density decreases below 10³ ions/cm³ and the magnetic field strength increases, the electromagnetic body force may become significant. The electromagnetic body force may also be significant in the nightside ionosphere. The bulk of the ionospheric flow momentum is not derived from the ionosheath momentum.