Wind-Driven Variability in the Prereversal Enhancement of the Equatorial Vertical Plasma Drift: Climatologies Observed by ICON

Abstract

The prereversal enhancement (PRE) is a brief surge in upward plasma velocity in the evening equatorial ionosphere and a driver of equatorial spread-F. This study reports the first PRE climatology from Ionospheric Connection Explorer (ICON) data, exhibiting seasonal and longitudinal variability that is qualitatively consistent with results from two previous satellite missions. Previous missions, however, lacked the neutral wind observations to characterize their impact on the PRE. To quantitatively assess wind impacts, numerical experiments are performed with a standalone dynamo solver using winds from the TIEGCM-ICON, which is driven from below by observed tides. To quantify the impact of solar/magnetic geometry, such as the alignment between the solar terminator and the magnetic meridian, the model was first driven with seasonally and longitudinally averaged winds (which includes seasonally averaged zonal-mean winds and migrating tides). This reproduces the observed PRE variability with a correlation of 0.44. Incorporating longitudinally and seasonally varying wind patterns improves the correlation to 0.68. This suggests that climatological wind variability is an important driver of PRE variability, but future work is needed to account for the missing variability. Potential missing drivers include conductivity variability near the terminator and mesoscale wind features such as the solar terminator wave.