Quiet-time day-to-day variability of equatorial vertical E × B drift from atmosphere perturbations at dawn

Ionospheric day-to-day variability is ubiquitous, even under undisturbed geomagnetic and solar conditions. In this paper, quiet-time day-to-day variability of equatorial vertical E × B drift is investigated using observations from ROCSAT-1 satellite and the Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension (WACCM-X) v2.1 simulations. Both observations and model simulations illustrate that the day-to-day variability reaches the maximum at dawn, and the variability of dawn drift is largest around June solstice at ~90-180°W. However, there are significant challenges to reproduce the observed magnitude of the variability and the longitude distributions at other seasons. Using a standalone electro-dynamo model, we find that the day-to-day variability of neutral winds in the E-region (≤~130 km) is the primary driver of the day-to-day variability of dawn drift. Ionospheric conductivity modulates the drift variability responses to the E-region wind variability, thereby determining its strength as well as its seasonal and longitudinal variations. Further, the day-to-day variability of dawn drift induced by individual tidal components of winds in June are examined: DW1, SW2, D0, and SW1 are the most important contributors.