Tidal Control of Equatorial Vertical E x B Drift Under Solar Minimum Conditions

Observations show that equatorial ionospheric vertical drifts during solar minimum differ from the climatology between late afternoon and midnight. By analyzing WACCM-X simulations, which reproduce this solar cycle dependence, we show that the interplay of the dominant migrating tides, their propagating and in situ forced components, and their solar cycle dependence impact the F-region wind dynamo. In particular, the amplitude and phase of the propagating migrating semidiurnal tide (SW2) in the F-region plays a key role. Under solar minimum conditions, the SW2 tide propagate to and beyond the F-region in the winter hemisphere, and consequently its zonal wind amplitude in the F-region is much stronger than that under solar maximum conditions. Furthermore, its phase shift leads to a strong eastward wind perturbation near local midnight. This in turn drives a F-region dynamo with an equatorial upward drift between 18 and 1 hr local times. The vertical ion motion in the equatorial ionosphere plays a key role in the space weather. Satellite observations found that such vertical motion during periods with low solar activity can be quite different from the known climatology, and the cause is not clear. Using a whole atmosphere general circulation model, WACCM-X, we are able to reproduce the pattern of the vertical ion motion similar to that observed during low activity solar cycle periods. By analyzing the model results, we find that the relative significance of the different atmosphere tidal wave components and its variation with solar activity contribute to the solar dependence of the vertical ion motion. The propagating altitudes of tide with 12-hr period, as well as where and when the tidal wind becomes large, are of particular importance. Upward equatorial vertical ion drift near midnight under solar minimum conditions reproduced by WACCM-X Modulation of F-region dynamo by propagating semidiurnal tide is much stronger during solar minimum Tidal phase change in equatorial F-region during solar minimum shifts upward drift toward midnight