Seasonal dependence of the longitudinal variations of nighttime ionospheric electron density and equivalent winds at southern midlatitudes

X Luan,X Dou

doi:10.5194/angeo-31-1699-2013

Abstract

Abstract. It has been indicated that the observed Weddell Sea anomaly (WSA) appeared to be an extreme manifestation of the longitudinal variations in the Southern Hemisphere, since the WSA is characterized by greater evening electron density than the daytime density in the region near the Weddell Sea. In the present study, the longitudinal variations of the nighttime F2-layer peak electron density at southern midlatitudes are analyzed using the observations of the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites between 2006 and 2008. It is found that significant longitudinal difference (> 150%) relative to the minimum density at each local time prevails in all seasons, although the WSA phenomenon is only evident in summer under this solar minimum condition. Another interesting feature is that in summer, the maximum longitudinal differences occur around midnight (~ 23:00–00:00 LT) rather than in the evening (19:00–21:00 LT) in the evening, when the most prominent electron density enhancement occurs for the WSA phenomenon. Thus the seasonal–local time patterns of the electron density longitudinal variations during nighttime at southern midlatitudes cannot be simply explained in terms of the WSA. Meanwhile, the variations of the geomagnetic configuration and the equivalent magnetic meridional winds/upward plasma drifts are analyzed to explore their contributions to the longitudinal variations of the nighttime electron density. The maximum longitudinal differences are associated with the strongest wind-induced vertical plasma drifts after 21:00 LT in the Western Hemisphere. Besides the magnetic declination–zonal wind effects, the geographic meridional winds and the magnetic inclination also have significant effects on the upward plasma drifts and the resultant electron density.

Highlights

In the Southern Hemisphere, significant longitudinal variations of the ionospheric electron density occurred at midlatitudes in evening due to the Weddell Sea anomaly (WSA)
The ionospheric F2-layer peak density retrieved from observations by COSMIC was used to analyze its longitudinal variations during nighttime at southern midlatitudes, where the prominent WSA occurs in Western Hemisphere in summer
The longitudinal difference is calculated by a relative ratio r, which is defined by the percentage difference relative to the minimum density along longitudes at a fixed local time

Summary

Introduction

In the Southern Hemisphere, significant longitudinal variations of the ionospheric electron density occurred at midlatitudes in evening due to the Weddell Sea anomaly (WSA). Several mechanisms are applied to explain these interesting phenomena, including the equatorward neutral wind, electric field, photoionization and the downward plasma diffusion from the plasmasphere (Burns et al, 2008, 2011; Jee et al, 2009; He et al, 2009; Chen et al, 2011, 2012; Liu et al, 2010; Lin et al, 2009; Zhang et al, 2011, 2012a, b; Zhao et al, 2013).

Results

Discussion

Conclusion