Thermospheric winds around the cusp region

An equatorward wind has been observed first by the balloon-borne Fabry-Perot interferometer called High-Altitude Interferometer Wind Observation on the equatorward side of the cusp near the local noon, which is opposite to the typical direction of neutral wind driven by the day-night pressure gradient. However, this dayside equatorward wind was not reproduced by the standard Thermosphere Ionosphere Electrodynamics General Circulation Model under the resolution of 5° longitude by 5° latitude (5°×5°). In this study, the Global Ionosphere Thermosphere Model has been run in different cases and under different resolutions to investigate the neutral dynamics around the cusp region. First, we compare the simulations with and without additional cusp energy inputs to identify the influence of cusp heating. Both runs have a resolution of 5°×1° (longitude × latitude) in order to better resolve the cusp region. After adding in the cusp energy, the meridional wind in simulation turns to be equatorward on the dayside, which is consistent with the observation. It indicates that strong heating in the cusp region causes changes in the pressure gradient around the cusp and subsequent variations in the neutral winds. The simulations with the same cusp heating specifications are repeated, but with different horizontal resolutions to examine the influence of resolution on the simulation results. The comparisons show that the resolution of 5°×1° can resolve the cusp region much more stably and consistently than the 5°×5° resolution.