The Turbulence Field Generated by a Linear Gravity Wave

Jerome Weinstock NOAA/Aeronomy Laboratory, Boulder, CO 80303

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Abstract

An approximate but standard turbulence closure—the so-called “1½ order closure”—is employed to calculate the turbulence field generated by a stationary, large amplitude gravity wave in the middle atmosphere. Turbulence is generated within the superadiabatic phases of the gravity wave and is damped within other phases of the wave. Turbulence collapse is accounted for in the damping region. Determined are the intensity (rms turbulence velocity) and the local turbulence diffusivity as a function of wave amplitude, frequency, wavelength and position in space. Also calculated is an a priori, although approximate, prediction of the wave amplitude required to saturate the gravity wave, and the degree of superdiabaticity at saturation. Simplifying approximations limit the calculations to 2HkzUk≫ 1.

The results are approximate because of the nature of the turbulence model but the qualitative results have simple explanations.

Abstract

An approximate but standard turbulence closure—the so-called “1½ order closure”—is employed to calculate the turbulence field generated by a stationary, large amplitude gravity wave in the middle atmosphere. Turbulence is generated within the superadiabatic phases of the gravity wave and is damped within other phases of the wave. Turbulence collapse is accounted for in the damping region. Determined are the intensity (rms turbulence velocity) and the local turbulence diffusivity as a function of wave amplitude, frequency, wavelength and position in space. Also calculated is an a priori, although approximate, prediction of the wave amplitude required to saturate the gravity wave, and the degree of superdiabaticity at saturation. Simplifying approximations limit the calculations to 2HkzUk≫ 1.

The results are approximate because of the nature of the turbulence model but the qualitative results have simple explanations.

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