Numerical modeling of equatorial spread F using observed neutral wind profiles

The neutral wind in the F region ionosphere near sunset is known to be a key driver of the nighttime F region plasma instabilities known as Equatorial Spread-F (ESF). Eastward winds drive vertical Pedersen currents that, in turn, drive the Rayleigh-Taylor mechanisms responsible for the large plumes of plasma depletion often seen in ESF events. Recent sounding rocket chemical tracer studies have shown large westward winds and wind shears in the equatorial F region during the period near sunset.Westward winds and shears of these magnitudes are unexpected based on current wind models, which show eastward neutral flow with very small vertical gradients above 200 km. It is typical for ionospheric models to use wind inputs from the Horizontal WindModel (HWM14) in order to model the development of ESF; however, the zonal wind profiles observed in these experiments are not consistent with this approximation during the transition hours near sunset. The rapid change in the winds across the evening terminator is particularly striking. In this study, we apply the observed chemical tracer neutral wind profiles to an existing ESF model in order to investigate the effects of such large westward winds and shears during the transitional period near sunset on the subsequent development of ESF plumes