Observation of the lunar tide in the middle atmosphere by the Aura Microwave Limb Sounder

Abstract

Because of the near-polar, sun-synchronous orbit of the Aura satellite, the Microwave Limb Sounder (Aura/MLS) observes the lunar tide as a lunar semimonthly variation of geopotential height and temperature in the middle atmosphere. The FFT spectrum of the mesospheric geopotential height time series from 2004 to 2021 shows a significant spectral peak at a period of 14.7653 d which is a half lunar month. The lunar tidal signal is clearer in geopotential height than in temperature. For the first time, the characteristics of the lunar tide in geopotential height (or pressure) are observed for the middle atmosphere. The latitudinal dependence of the observed mesospheric lunar tidal amplitude is in a good agreement with the numerical simulation of Geller. The climatology of the lunar tide shows larger amplitudes in January than in July at low latitudes, in agreement with the simulation. Generally, the observed lunar tide in geopotential height is smalller by a factor 2–3 than the simulated lunar tide. The vertical phase gradient of the observed lunar tide agrees well with the simulated vertical phase gradient.