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 (∼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°–120°W and 30°W–60°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°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.

The Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) was launched aboard NASA’s Ionospheric Connection (ICON) Explorer satellite in October 2019 to measure winds and temperatures on the limb in the upper mesosphere and lower thermosphere (MLT). Temperatures are observed using the molecular oxygen atmospheric band near 763 nm from 90–127 km altitude in the daytime and 90–108 km in the nighttime. Here we describe the measurement approach and methodology of the temperature retrieval, including unique on-orbit operations that allow for a better understanding of the instrument response. The MIGHTI measurement approach for temperatures is distinguished by concurrent observations from two different sensors, allowing for two self-consistent temperature products. We compare the MIGHTI temperatures against existing MLT space-borne and ground-based observations. The MIGHTI temperatures are within 7 K of these observations on average from 90–95 km throughout the day and night. In the daytime on average from 99–105 km, MIGHTI temperatures are higher than coincident observations by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on NASA’s TIMED satellite by 18 K. Because the difference between the MIGHTI and SABER observations is predominantly a constant bias at a given altitude, conclusions of scientific analyses that are based on temperature variations are largely unaffected.

18 Observations of the nighttime thermospheric wind from two ground-based Fabry19 Perot Interferometers are compared to the level 2.1 and 2.2 data products from the Michel20 son Interferometer Global High-resolution Thermospheric Imaging (MIGHTI) onboard 21 NASA’s Ionospheric Connection Explorer (ICON) to assess and validate the method22 ology used to generate measurements of neutral thermospheric winds observed by MIGHTI. 23 We find generally good agreement between observations approximately coincident in space 24 and time with mean differences less than 11 m/s in magnitude and standard deviations 25 of about 20-35 m/s. These results indicate that the independent calculations of the zero26 wind reference used by the different instruments do not contain strong systematic or phys27 ical biases, even though the observations were acquired during solar minimum conditions 28 when the measured airglow intensity is weak. We argue that the slight differences in the 29 estimated wind quantities between the two instrument types can be attributed to gra30 dients in the airglow and thermospheric wind fields and the differing viewing geometries 31 used by the instruments. 32 Plain Language Summary 33 This study presents a validation of observations made by two different types of in34 struments used to measure nighttime thermospheric neutral winds. These winds repre35 sent the motion of neutral particles in the thermosphere and studying their properties 36 is critical to gaining a complete understanding of the dynamics of the Earth’s upper at37 mosphere. We use observations made by two ground-based Fabry-Perot interferometers 38 to validate measurements from the Michelson Interferometer for Global High-resolution 39 Thermospheric Imaging (MIGHTI) onboard NASA’s recently-launched Ionospheric Con40 nection Explorer (ICON) satellite. After identifying observations from the different in41 struments that are coincident in space and time, we show that the measurements are sta42 tistically highly correlated, thereby successfully validating the MIGHTI thermospheric 43 wind observations. 44

The thermospheric wind is a critical geophysical parameter for understanding the behavior of the Earth's upper atmosphere. Global-scale characterization of this parameter is needed to enable improved specification and forecasting of the near space environment. Global-scale measurements of horizontal wind vectors versus altitude have been performed from satellites using a variety of techniques, but the available data are still sparse. To address some of the challenges presented by space-based thermospheric wind measurement, the Doppler Asymmetric Spatial Heterodyne (DASH) technique has recently been developed. Here we present results of a ground-based validation of the DASH technique. The successful validation was performed by conducting collocated ground-based measurements with an instrument that uses the well established Fabry–Perot interferometer technique. Due to cloud cover and a limited observation period, data for only one night of simultaneous observations with minor cloud interference were obtained. The wind velocities observed by the two techniques show good overall agreement, but differences larger than the combined uncertainties are present at times. Contributions to these larger disagreements could be due to cloud interference, the minor differences in the observation geometry, or a non-zero vertical wind. A comparison of this single night of data with the Horizontal Wind Model (HWM07) climatology shows differences of up to about 100m/s on timescales of less than an hour to several hours.