Seasonal Variability of the DE3 Tide at 160 km Altitude Based on GOLD Observations (2019–2023) (Special Issue in Honor of Professor Xiao Zuo’s 90th Birthday)

This study aims to reveal the seasonal evolution characteristics of atmospheric tides in the middle thermosphere (160 km) and fill the observational gap in the 110–200 km "thermospheric gap" region. Based on the geostationary orbit observation data from NASA's GOLD mission during 2019–2023, the spatio-temporal sequences of amplitude and phase of the non-migrating diurnal tide (DE3) are extracted from the temperature field using the wavenumber spectrum analysis method and weighted least squares fitting, combined with Empirical Orthogonal Function (EOF) decomposition to analyze its dominant modes. The results show that the DE3 tide at 160 km exhibits distinct seasonal characteristics compared with those in the mesosphere and lower thermosphere (MLT), with its amplitude peak stably locked after the autumnal equinox (September–November). The explosive enhancement and phase mutation occurring in the autumn of 2021 reveal the nonlinearity and complexity of tidal dynamic processes at this altitude. EOF analysis further confirms that the DE3 signal is not dominated by a single mode but is jointly constructed by the equatorial symmetric mode and the hemispheric asymmetric regulatory mode. This study verifies that the autumn peak structure is an inherent climatological attribute of the tide at this altitude, providing key observational evidence for understanding the synergistic modulation of lower atmospheric forcing and thermospheric in-situ processes.