Daytime Thermospheric Wind Transients and Circulation in May 2021

Abstract

Changes in the thermospheric wind originating in storm-time transients in high-latitude Joule heating and ion circulation are effective in modifying conditions throughout Earth's upper atmosphere and ionosphere. Among the effects these drivers can produce are large-scale gravity waves (GWs), characterized by significant wind transients that propagate away from the auroral zone, driving transient ion motion during their 1–2 hr passage. Longer period changes in mean winds can develop over the following hours to days, depending on the duration and magnitude of the high latitude heating, and also extend globally. The effectiveness of these processes in modifying the mean density of the daytime ionosphere likely depends on the extent to which these disturbances reach the daytime equatorial region and downward into the E-region wind dynamo (below $\sim$180 km). A study of a month of observations made during the ICON mission reveals the variety of behaviors with both transient effects and longer-term changes in mean winds. The duration of auroral inputs, as opposed to the average input over time, is identified as important to the development of dynamo-modifying zonal disturbance winds. During geomagnetic disturbances, we find that the predictive capability of a general circulation model (TIEGCM) for meridional wind transport is good (R $>$ .8) while the storm-time zonal wind transport is harder to predict (R $>$ .5). This study is the first of its kind, measuring winds and storm responses continuously for a month in both the daytime E- and F- regions simultaneously with $\sim$97 min cadence.