Simulated equinoctial asymmetry of the ionospheric vertical plasma drifts

Abstract

This paper studies the influence of the lower thermospheric tidal winds below 105 km on the equinoctial asymmetry of the equatorial vertical E × B plasma drifts (V⊥) using Theoretical Ionospheric Dynamo Model II of the Institute of Geology and Geophysics, Chinese Academy of Sciences (TIDM‐IGGCAS‐II) and tidal winds below 105 km from thermosphere‐ionosphere‐mesosphere‐energetics‐dynamics satellite Doppler Interferometer (TIDI) observations. Although a series of other nonmigrating tides also affect the V⊥ asymmetry, the simulated equinoctial asymmetry in V⊥ are mainly driven by the migrating diurnal tide (DW1), migrating semidiurnal tide (SW2), DE3, and DW2 nonmigrating tides. The asymmetry in daytime V⊥ varies with local time and longitude and mainly shows three features. First, the simulated daytime V⊥ during the March equinox is larger than that during the September equinox in most of longitudinal sectors. This asymmetry is mainly driven by the semiannual oscillation (SAO) of the migrating diurnal tide in the tropical mesosphere‐lower thermosphere (MLT) region, and the equinoctial asymmetry of the migrating semidiurnal tide also plays an important role in the generation of this asymmetry. Second, the daytime V⊥ asymmetry in the Eastern Hemisphere is more significant than that in the Western Hemisphere. Our simulation suggests that the longitudinal variations of the geomagnetic fields and DW2 tides play important roles in the generation of this hemisphere difference. Third, there is an obvious wave number 4 longitudinal structure in the V⊥ asymmetry. Our simulation suggests that this wave number 4 structure is mainly driven by the equinoctial asymmetry of the DE3 tide.