Longitudinal Structure of the Midlatitude Ionosphere Using COSMIC Electron Density Profiles

Abstract

Longitudinal variations of electron density (Ne) near zero magnetic declination lines at midlatitude ionosphere have been disclosed earlier in some longitude regions. However, its global picture remains unclear. In this study, Ne at midlatitudes (40–50° magnetic latitude) within 170- to 550-km altitudes obtained from Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites for low solar activity (2006–2011) are used to investigate the local time, seasonal, altitudinal, and hemispheric variations of ΔNe (difference between Ne and its zonal mean). Results indicate (1) ΔNe showing different patterns below 180 km and above 220 km and (2) an eastward phase shift of ΔNe above 220 km. The ΔNe above 220 km shows wave-1 longitudinal structure during forenoon in northern winter, which differs from the wave-2 longitudinal structure in other seasons. The ΔNe below 180 km presents solstice asymmetries and wave-1 longitudinal structures. (3) On average, ΔNe above 220 km is stronger in North American sector (30–150°W) by 32% compared to Europe-Asian sector (30–150°E), and it is also stronger in Southern Hemisphere by 35% than in Northern Hemisphere. The wave-1 longitudinal structure below 180 km is due to the latitudinal difference of solar zenith angle in magnetic coordinates. The ΔNe above 220 km has high consistency with that of ΔhmF2 (peak height) indicating significant effects of neutral wind dynamics. Results of the empirical model Horizontal Wind Model 14 further disclose that the vertical drifts due to zonal wind (via magnetic declination) and meridional wind (via its zonal difference) are responsible for the longitudinal structures in ΔNe above 220 km.