Biennial Signature in the Equatorial Upper Mesospheric DW1 Amplitudes During Boreal Fall Equinox and Its Relationship With Stratospheric Ozone

Interannual variability of the migrating diurnal tide (DW1) in the equatorial upper mesosphere lower thermospheric region has been studied using long‐term (2003–2024) temperature data obtained from the Sounding of Atmosphere using Broadband Emission Radiometry (SABER) instrument on board the Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics (TIMED) satellite. The DW1 tidal amplitude exhibits consistent biennial variability in the recent years during the boreal fall equinox months (September–October). It is interesting to note that the stratospheric ozone volume mixing ratio (vmr) at 31 hPa obtained from the Microwave Limb Sounder instrument on board the Aura satellite also shows similar biennial variability. However, the positive anomaly of DW1 coincides with the negative anomaly in Total Column Water Vapor (TCWV), obtained from the European Centre for Medium Range Weather Forecasts (ECMWF) Reanalysis v5 (ERA5) data sets. Besides, during September–October, the TCWV shows a low value close to its seasonal minimum, while the ozone vmr is larger, comparable to its seasonal maximum. Biennial variability is also observed in the heating rates of four lowest order classical Hough modes, calculated from ozone values at 31 hPa and in their corresponding tidal amplitudes, estimated using Laplace Tidal Equation, with (1, 1) tidal mode showing the maximum amplitude. Hence, it is suggested that the biennial variability in the DW1 tide at 100 km observed consistently during boreal fall equinox months in the recent years is likely driven by the (1, 1) tidal mode variability generated due to the stratospheric ozone heating at 31 hPa.