Estimate eddy diffusion coefficients from gravity wave vertical momentum and heat fluxes

Abstract

A method was presented to estimate the eddy momentum and thermal diffusion coefficients from the gravity wave momentum and heat fluxes based on linear saturation theory. This method was applied using the fluxes between 85–100 km altitude measured by a Na wind/temperature lidar at Starfire Optical Range, NM (35N, 106.5W). The seasonal and altitude variations of the diffusion coefficients and Prandtl number were estimated. It is found that both diffusion coefficients are small in spring and fall and large in winter and summer. The annual mean momentum diffusion coefficient is about 400 m2/s between 85–100 km; the thermal diffusion coefficient decreases from 400 m2/s at 85 km to 100 m2/s at 100 km, resulting in a Prandtl number that increases with altitude from 1 to over 3.