Eddy diffusion coefficients due to instabilities in internal gravity waves

Abstract

Internal gravity waves in the upper atmosphere tend to grow in amplitude with increasing height to maintain continuous vertical transport of wave energy. The growth of amplitude of a wave is limited by convective instabilities that must form at the height where the temperature oscillation becomes great enough to include a superadiabatic region. This turbulence attenuates the wave by eddy transport of heat and viscous stress through the wave structure, essentially maintaining a constant amplitude of the wave at greater altitudes. Eddy diffusion coefficients of the order of 107 cm²/sec are readily produced by typical gravity waves near the mesopause. Since an average coefficient of only 106 cm²/sec is sufficient to explain the thermal structure of the mesopause region, sporadic turbulence produced by instabilities in gravity waves is probably an important process of the upper atmosphere.