# Influence of parameterized small-scale gravity waves on the migrating diurnal tide in Earth's thermosphere

## TL;DR

This study investigates how parameterized small-scale gravity waves influence the diurnal migrating tide in Earth's thermosphere, revealing their significant impact on circulation, temperature, and tidal amplitudes across different latitudes and conditions.

## Contribution

It introduces a comprehensive gravity wave parameterization in a general circulation model to accurately simulate their effects on thermospheric tides and circulation.

## Key findings

- Gravity waves cool the thermosphere by up to 12-18%.
- GWs can either enhance or reduce tidal amplitudes depending on phase correlation.
- Proper GW parameterization is essential for realistic GCM simulations.

## Abstract

Effects of subgrid-scale gravity waves (GWs) on the diurnal migrating tides are investigated from the mesosphere to the upper thermosphere for September equinox conditions, using a general circulation model coupled with the extended spectral nonlinear GW parameterization of Yi\u{g}it et al (2008). Simulations with GW effects cut-off above the turbopause and included in the entire thermosphere have been conducted. GWs appreciably impact the mean circulation and cool the thermosphere down by up to 12-18%. GWs significantly affect the winds modulated by the diurnal migrating tide, in particular in the low-latitude mesosphere and lower thermosphere and in the high-latitude thermosphere. These effects depend on the mutual correlation of the diurnal phases of the GW forcing and tides: GWs can either enhance or reduce the tidal amplitude. In the low-latitude MLT, the correlation between the direction of the deposited GW momentum and the tidal phase is positive due to propagation of a broad spectrum of GW harmonics through the alternating winds. In the Northern Hemisphere high-latitude thermosphere, GWs act against the tide due to an anti-correlation of tidal wind and GW momentum, while in the Southern high-latitudes they weakly enhance the tidal amplitude via a combination of a partial correlation of phases and GW-induced changes of the circulation. The variable nature of GW effects on the thermal tide can be captured in GCMs provided that a GW parameterization (1) considers a broad spectrum of harmonics, (2) properly describes their propagation, and (3) correctly accounts for the physics of wave breaking/saturation.