Non-Migrating Structures in the Northern Midlatitude Thermosphere During December Solstice Using ICON/MIGHTI and FPI Observations

Midlatitude thermospheric wind observations from the Michelson Interferometer for Global High-resolution Thermospheric Imaging on board the Ionospheric Connections Explorer (ICON/MIGHTI) and from the ground-based Boulder, Urbana, Millstone Hill and Morocco Fabry-Perot interferometers (FPIs) are used to study a distinct solar local time (SLT) evolution in the nighttime wind field around the December solstice period. Our results show, to the best of our knowledge for the first time, strong non-migrating tides in midlatitude thermospheric winds using coincident from different observing platforms. These observations exhibited a structure of strong (similar to 50-150 m/s) eastward and southward winds in the pre-midnight sector (20:00-23:00 SLT) and in the post-midnight sector (02:00-03:00 SLT), with a strong suppression around midnight. Tidal analysis of ICON/MIGHTI data revealed that the signature before midnight was driven by diurnal (D0, DE1, DE2, DW2) and semidiurnal (SE2, SE3, SW1, SW4) tides, and that strong terdiurnal (TE2, TW1, TW2, TW5) and quatradiurnal (QW2, QW3, QW6) tides were important contributors in the mid- and post-midnight sectors. ICON/MIGHTI tidal reconstructions successfully reproduced the salient structures observed by the FPI and showed a longitudinal dual-peak variation with peak magnitudes around 200 degrees-120 degrees W and 30 degrees W-60 degrees E. The signature of the structure extended along the south-to-north direction from lower latitudes, migrated to earlier local times with increasing latitude, and strengthened above 30 degrees N. Tidal analysis using historical FPI data revealed that these structures were often seen during previous December solstices, and that they are much stronger for lower solar flux conditions, consistent with an upward-propagating tidal origin.