Effective vertical diffusion by atmospheric gravity waves

Current parameterization schemes suffer from oversimplification and often underestimate the transport rate. In this study, a new approach is explored to quantify the effective vertical eddy diffusion by using a high-resolution Whole Atmosphere Community Climate Model (WACCM) simulation based on scale invariance.

The WACCM simulation can partially resolve the mesoscale GW spectrum down to 250 km horizontal wavelength, and the heat flux and the effective vertical eddy diffusion by these waves are calculated directly. The effective vertical diffusion by the smaller-scale, unresolved waves, is then deduced based on scale invariance, following the method outlined by H.-L. Liu (2019) in quantifying GW momentum flux and forcing. The effective vertical diffusion obtained is generally larger than that obtained from parameterizations, and is comparable with that derived from observations in the mesosphere and lower thermosphere region.