Evidence for enhanced dynamic flow in ionospheric holes from the Pioneer Venus Orbiter Neutral Mass Spectrometer

Ion mode measurements made by the Pioneer Venus Orbiter Neutral Mass Spectrometer (ONMS) for two ionospheric holes on orbit numbers 530 and 531 were used to find evidence for enhanced dynamic flow in ionospheric holes. The analysis of the spin modulation has provided measurements of one component of the ion drift in the hole regions. It was found that, inside the holes, the He(+)/O(+) ratio is enhanced relative to that occurring outside the holes. The in drift direction in the ecliptic plane for the hole regions was found to be consistent with downward ion flow (i.e., toward the planet) and, for one orbit examined without a hole, with upward ion flow at the approach of ionopause. The ONMS measurements in the hole and near the ionopause suggest that both areas are regions of enhanced dynamic flow.