Neutral Temperature Measurements from ICON/MIGHTI and TIMED/SABER: Tidal and Conjunction Analysis

We present a cross-comparison between ICON/MIGHTI and TIMED/SABER mesosphere and lower thermosphere neutral temperature measurements between 90 and 110 km covering the Northern Hemisphere up to mid latitudes and Southern Hemisphere low latitudes. We analyze MIGHTI and SABER temperatures and identify their conjunctions using a narrow space-time window around each SABER temperature measurement. The analysis found frequent conjunctions spread over all longitudes, providing an unprecedented opportunity for a cross-calibration study of MLT neutral temperatures measured by two independent space-based optical sensors. The influence of non-migrating tides is clearly evident in measurements from both instruments when the data are assembled from conjunctions at a fixed local time and all longitudes. We present a detailed statistical analysis of conjunctions as a function of latitude, longitude, seasons, and local time. By leveraging the significant geospatial and temporal spread of the conjunctions over multiple years, this study serves as a large-scale cross-validation of ICON/MIGHTI and TIMED/SABER temperatures.

Furthermore, we compare major tidal components (DW1, SW2, DE3, etc.) of the MLT region computed using a running window method (41-day for MIGHTI and 61-day for SABER) between 90-105 km. We discuss the observed tidal discrepancies in relation to latitude, altitude, and season. We find that the largest discrepancies between MIGHTI and SABER temperatures and computed tidal amplitudes and phases start above 100 km. The discrepancies are discussed in the context of the retrieval methodologies employed for each instrument. Finally, we compare these observations with state-of-the-art numerical simulations from TIMEGCM/MERRA2 and TIEGCM/HME(ICON) to better understand SABER-MIGHTI discrepancies in the context of existing community knowledge of tidal behavior in the lower thermosphere.