The effect of breaking gravity waves on the dynamics and chemical composition of the mesosphere and lower thermosphere

TLDR

A two‑dimensional dynamical/chemical model incorporating gravity‑wave drag and diffusion was used to study the influence of breaking gravity waves on the 60‑110 km mesosphere and lower thermosphere. Breaking gravity waves deposit momentum that reverses zonal winds, drives a strong mean meridional circulation, produces a cold summer and warm winter mesopause, and generates seasonal eddy diffusion patterns that agree with radar and airglow observations, confirming gravity waves’ key role in shaping the zonally averaged structure of the mesosphere and lower thermosphere.

Abstract

The influence of breaking gravity waves on the dynamics and chemical composition of the 60‐ to 110‐km region has been investigated with a two‐dimensional dynamical/chemical model that includes a parameterization of gravity wave drag and diffusion. The momentum deposited by breaking waves at mesospheric altitudes reverses the zonal winds, drives a strong mean meridional circulation, and produces a very cold summer and warm winter mesopause, in general agreement with observations. The seasonal variations of the computed eddy diffusion coefficient are consistent with the behavior of mesospheric turbulence inferred from MST radar echoes. In particular, it is found that eddy diffusion is strong in summer and winter but much weaker at the equinoxes and that this seasonal behavior has important consequences for the distribution of chemical species. Comparison between computed atomic oxygen and ozone, and the abundances of these constituents inferred from the 557.7‐nm and 1.27‐μm airglow emissions, reveals excellent agreement. The consistency between model results and these diverse types of observations lends strong support to the hypothesis that gravity waves play a very important role in determining the zonally averaged structure of the mesosphere and lower thermosphere.