Local Time Variations of Quiet Time Meridional Winds During Solar Minimum Solstices Based on ICON Observations and Numerical Simulations

Abstract

ICON observations were used to investigate local time (LT) and latitudinal variations of thermospheric meridional winds in the middle-high thermosphere (160–300 km) during quiet times in 2020 June and December. At middle-low latitudes (10°S–40°N), meridional winds were predominantly equatorward in the summer hemisphere while mostly poleward in the winter hemisphere. The meridional winds showed that the diurnal variation was dominant between ∼20°N and ∼40°N, but the semi-diurnal variation played a leading role at lower latitudes (below ∼20°N) during solstice months. Thermosphere-Ionosphere Electrodynamics General Circulation Model reproduced the ICON observed meridional wind variations qualitatively. A model diagnostic analysis shows that the pressure gradient force dominated the semi-diurnal variation of the winds, while the Coriolis force played a leading role in the diurnal variation in June. In December, LT variations of meridional winds were primarily driven by pressure gradient and ion drag forces. During both months, the vertical viscosity was important, tending to balance the effects of pressure gradients. Additionally, semi-diurnal variations of low-latitude meridional winds in June were more affected by upward propagating tides than those in December.