Observational Evidence for the Influence of Diurnal Tide in Driving Winds in the Polar Upper Mesosphere and Lower Thermosphere.

The meteor radar wind observations over Esrange (67.9°N, 21.10°E) and Rothera (67.5°S, 68.1°W), located respectively in the northern and southern polar latitudes show seasonal variation in the upper mesosphere and lower thermosphere (UMLT) winds with strong westward flow in the zonal wind and equatorward flow in the meridional wind during April‐September over Esrange and October‐February over Rothera. The semi‐diurnal tide shows larger amplitudes over Esrange than over Rothera. However, the diurnal tide (DT) shows comparable amplitudes in both stations. The DT amplitude decreases with height over both stations. Significant correlations between the DT amplitude and mean zonal wind (−0.74 for Esrange and −0.54 and −0.77 for Rothera) indicate the possible role of DT in driving the westward winds. The space‐time spectral analysis of the temperature obtained from the radiance observations of the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instrument on board the TIMED (Thermosphere Ionosphere Mesosphere Energetics Dynamics) satellite reveals the summer maximum of migrating diurnal tide of zonal wavenumber 1 (DW1) over both 60°N and 60°S, indicating that the DT is mostly composed of DW1. These results suggest that the westward winds in the polar UMLT region are largely driven by the westward momentum contributed by the DW1 tide due to its interaction with the background wind. Plain Language Summary: The study provides an observational evidence for the influence of tides on the background wind flow at the polar upper mesospheric heights. The meteor radar observations over two polar latitude stations are used to study the seasonal and interannual variation of winds and investigate whether there is any relation between winds and tides. It is observed that stronger westward wind flows at the upper mesosphere lower thermospheric heights when the amplitude of diurnal tide is larger. Moreover, the amplitude of the diurnal tides is found to decrease with height, unlike the semi‐diurnal tidal amplitude, indicating the interaction of diurnal tide with background flow. Due to the tidal mean flow interaction, the diurnal tide which is mostly the westward propagating migrating diurnal tide (DW1), can drive the large westward wind through its westward momentum deposition into the background flow. Key Points: Strong westward winds are observed when the amplitude of westward propagating diurnal tide is largerThe semi‐diurnal tidal amplitude increases with height, while the diurnal tidal amplitude decreases with heightDiurnal tide being the major source of westward momentum possibly drives the zonal wind flow due to its interaction with background flow [ABSTRACT FROM AUTHOR]