Simulations of the equatorial thermosphere anomaly: Field-aligned ion drag effect

In this paper the impact of the field-aligned ion drag on equatorial thermosphere temperature and density is quantitatively investigated on the basis of the National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model (NCAR TIEGCM) simulations under high solar activity (F107 = 180). The increase of upward vertical winds over the magnetic equator associated with the additional divergence of meridional winds, caused by the inclusion of field-aligned ion drag, leads to a reduction in thermosphere temperature and density at the magnetic equator through enhanced adiabatic cooling.

We found that the field-aligned ion drag has an obvious impact on the thermosphere only over the magnetic equatorial region in the daytime and evening sectors, whereas it has less effect on the equatorial thermosphere anomaly (ETA) crests. The daytime neutral temperature over the magnetic equator is reduced by about 30 K, for altitudes above 250 km without significant altitudinal variations, when field-aligned ion drag is included in the simulation.