Vertical Coupling by Solar Semidiurnal Tides in the Thermosphere From ICON/MIGHTI Measurements

摘要

Wind measurements from the Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) instrument on the Ionospheric CONnections (ICON) mission provide new insights into the semidiurnal tidal spectrum in the thermosphere, covering latitudes 9°S–39°N and altitudes 100–280 km altitude throughout 2020. Latitude vs. day of year (DOY) variability of solar semidiurnal tides SE2, S0, SW1, SW2, SW3, and SW4 at 250 km are presented for the first time, and evaluated relative to similar results at 106 km. Using daytime-only data, height vs. latitude and height vs. DOY variability of SE2, S0, SW1. SW3, and SW4 amplitudes and phases are depicted for the first time, revealing the effects of a dissipative thermosphere on the vertical evolutions of these tidal structures. SW2 is absent from these depictions due to potential aliasing by zonal mean winds. The above results are considered in light of the Climatological Tidal Model of the Thermosphere (CTMT), which is based on fits to tidal winds and temperatures from the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics mission between 80 and 120 km during 2002–2008, and extrapolated to an altitude of 400 km based on modeled tidal structures propagating in a dissipative thermosphere, but without in situ sources of excitation due to tide-tide or tide-ion drag nonlinear interactions. On the basis of comparisons with the CTMT and other characteristics revealed in the MIGHTI tidal structures, it is concluded that in situ sources exist for S0, SW1, SW2, and SW3 in the thermosphere above about 200 km.