Characterization of the Thermospheric Mean Winds and Circulation during
Solstice using ICON/MIGHTI Observations
Abstract
Using the horizontal neutral wind observations from the MIGHTI
instrument onboard NASA’s ICON (Ionospheric Connection Explorer)
spacecraft with continuous coverage, we determine the climatology of the
mean zonal and meridional winds and the associated mean circulation at
low- to middle latitudes (10S-45N) for Northern Hemisphere solstice
conditions between 90 km and 200 km altitudes, specifically on 20 June
2020 solstice as well as for a one-month period from 8 June-7 July 2020.
The data are averaged within appropriate altitude, longitude, latitude,
solar zenith angle, and local time bins to produce mean wind
distributions. The geographical distributions and local time variations
of the mean horizontal circulation are evaluated. The instantaneous
horizontal winds exhibit a significant degree of spatiotemporal
variability often exceeding ~150 m/s. The daily averaged
zonal mean winds demonstrate day-to-day variability. Eastward zonal
winds and northward (winter-to-summer) meridional winds are prevalent in
the lower thermosphere, which provides indirect observational evidence
of the eastward momentum deposition by small-scale gravity waves. The
mean neutral winds and circulation exhibit smaller scale structures in
the lower thermosphere (90-120 km), while they are more homogeneous in
the upper thermosphere, indicating the increasingly dissipative nature
of the thermosphere. The mean wind and circulation patterns inferred
from ICON/MIGHTI measurements can be used to constrain and validate
general circulation models, as well as input for numerical wave models.