Comparison of ICON/MIGHTI and TIMED/TIDI Neutral Wind Measurements in the Lower Thermosphere.

This study cross-compares ICON/MIGHTI and Thermosphere, Ionosphere, Mesosphere Energetics & Dynamics (TIMED)/TIMED Doppler Interferometer (TIDI) MLT region neutral winds from middle Northern Hemisphere to low Southern Hemisphere latitudes. We utilized MIGHTI level-2.2 (v4) and TIDI level-3 (v11) neutral winds from January 2020 to November 2020 and found their conjunctions using a space-time window of LST ± 15 min, latitude ± 4°, and longitude ± 4° around each TIDI wind measurement. Due to the nature of their orbital geometry, frequent conjunctions occurred between MIGHTI and TIDI. These conjunctions are spread in longitudes and they occur at approximately fixed LSTs and latitudes, which allows us to compare their observed diurnal variability. MIGHTI and TIDI wind observations agree well (except on the TIDI coldside during forward flight) and show similar large amplitude longitudinal variations that can reach more than 100 m/s. MIGHTI and TIDI zonal and meridional winds show moderate correlations of 0.60 and 0.55, respectively. The slopes of regression fits for zonal and meridional winds are 0.92 and 0.91, respectively. The root mean square differences in zonal and meridional winds are 56 and 66 m/s, respectively. We found that TIDI coldside measurements in forward flight show a systematic bias and this behavior is repetitive as the instrument pointing direction is changed by the periodic TIMED yaw maneuver. The nature of this systematic bias suggests that the TIDI zero-wind references (at least for the coldside telescopes) need revision. This investigation can provide guidance toward improving the TIDI data analysis. In addition, the results of this study act as a validation of MIGHTI MLT winds.