On a simple, data-aided analytic description of the morphology of equatorial F-region zonal plasma drifts

Abstract

We present results of an effort to evaluate the ability of an analytic model to describe the behavior of the equatorial zonal plasma drifts given inputs provided by readily available climatological models of thermospheric and ionospheric parameters. In a data-model fusion approach, we used vertical drift measurements to drive the model and zonal drift measurements to evaluate its output. Drift measurements were made by the Jicamarca incoherent scatter radar, and model results were evaluated for different seasons and two distinct solar flux conditions. We focused, in particular, on model results for different versions of the Horizontal Wind Model (HWM 97, 07, and 14). We found that, despite its simplicity, the analytic model can reproduce fairly well most of the features in the observed zonal plasma drifts, including the vertical shear associated with the evening plasma vortex. During daytime hours the model predicts similar results for the zonal drifts independently of the HWM used to drive the model. More importantly, the modeled daytime drifts match exceptionally well the behavior and magnitude of the observed drifts for all seasons and solar flux conditions considered. The nighttime results drive the overall performance of the analytic model, and we found that a single HWM cannot provide the best results for all seasons and solar flux conditions. We also examined the main sources of zonal drift variability. Most of the morphology is controlled by the zonal wind dynamo term of the analytic model, but with non-negligible contribution from the vertical drift term. Finally, we examined the contribution from the E- and F-region to the zonal wind dynamo. The morphology of the zonal drifts in the region of observation (240–560 km altitude) is controlled mostly by the F-region winds, but with significant contributions from the daytime E-region particularly during December solstice and low solar flux conditions.