Interactions between Gravity Waves and the Diurnal Tide in the Mesosphere and Lower Thermosphere

TLDR

The study investigates how breaking internal gravity waves with phase speeds of 0, ±10, ±20, and ±30 m s⁻¹ interact with the diurnal tide in the 70–120 km mesosphere and lower thermosphere using a time‑dependent numerical tide model. Gravity‑wave breaking and stress are computed with a modified Lindzen parameterization that accounts for diurnally varying zonal winds, and the interactions are restricted to extratropics to avoid WKB approximation issues. The results show that gravity‑wave stress suppresses the diurnal tide’s amplitude everywhere in the upper mesosphere and lower thermosphere, while also generating substantial semidiurnal and terdiurnal tides.

Abstract

Interactions between breaking internal gravity waves with phase speeds of 0, ±10, ±20, ±30ms-1, and the diurnal tide in the mesosphere and lower thermosphere (70-120km) are investigated using a time dependent numerical model of the tide. The gravity wave breaking and stress are calculated using a modified Lindzen's parameterization making allowance for interactions with a diurnally varying zonal wind superimposed on a zonal mean wind field. In order to avoid difficulties with the WKB approximation used in the parameterization, the interactions are only considered in the extratropics. However, the gravity wave stress is shown to suppress the amplitude of the diurnal tide at all latitudes in the upper mesosphere and lower thermosphere. It is also shown that gravity wave stresses modified by the diurnal tide induce significant semidiurnal and terdiurnal tides in the mesosphere and thermosphere.