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

Samuel A Shidler,Fabiano S Rodrigues

doi:10.1186/s40645-021-00417-8

Samuel A Shidler, Fabiano S Rodrigues

Open Access

https://doi.org/10.1186/s40645-021-00417-8

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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.

Highlights

Equatorial vertical E × B drifts are well-recognized as playing an important role in the linear stability of the equatorial F-region and in space weather (e.g., Abdu et al 1983; Fejer et al 1999; Kudeki and Bhattacharyya 1999; Hysell and Kudeki 2004; Kelley and Retterer 2008; Huang and Hairston 2015; Smith et al 2015; Huang 2018)
We found that the E-region dynamo contribution to daytime F-region zonal drifts decreases with solar flux as indicated by the results presented in the bottom panels of Figs. (LSF) and (HSF)
4 Conclusions Currently, a climatological model of the equatorial ionospheric zonal E×B drifts as a function of both local time and height has yet to be developed

Summary

Introduction

Equatorial vertical E × B drifts are well-recognized as playing an important role in the linear stability of the equatorial F-region and in space weather (e.g., Abdu et al 1983; Fejer et al 1999; Kudeki and Bhattacharyya 1999; Hysell and Kudeki 2004; Kelley and Retterer 2008; Huang and Hairston 2015; Smith et al 2015; Huang 2018). The convergence of our analytic model for all the HWM drivers during daytime hours is a result of the relatively weak differences in the field-line averaged zonal neutral winds (UφP) between each HWM model.

Results

Conclusion