Radiative Damping Revisited: Parameterization of Damping Rate in the Middle Atmosphere

Xun Zhu Department of Earth and Planetary Sciences, The Johns Hopkins University, Baltimore, Maryland

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Abstract

Radiative damping rates of temperature perturbations are calculated by CO2 and O3 Curtis matrices extending from the surface to 120 km in the earth's atmosphere with the eigenvalue and scale-dependent Newtonian cooling methods at 0.5 km of vertical resolution. Based on the latest value of the deactivation rate of CO2 bending mode by atomic oxygen, the radiative damping rate in the region of 90–100 km is ∼1.3 day −1 due to the near-local thermodynamic equilibrium nature of CO2 15-μm band emission. This is comparable to the damping rate induced by eddy and molecular diffusion of ∼2.5 day−1 in the corresponding region. It is also found that the radiative damping of the temperature perturbation in the winter polar mesopause is more than a factor 3 greater than in the summer polar mesopause. A simple and accurate parameterization for the scale-dependent damping rate as a function of altitude for any temperature profile is derived and tested with a zonally averaged model atmosphere. The typical percentage error of such a simple parameterization is about 10%–20%. This parameterization can be used in models of wave-zonal flow interaction in the earth's middle atmosphere.

Abstract

Radiative damping rates of temperature perturbations are calculated by CO2 and O3 Curtis matrices extending from the surface to 120 km in the earth's atmosphere with the eigenvalue and scale-dependent Newtonian cooling methods at 0.5 km of vertical resolution. Based on the latest value of the deactivation rate of CO2 bending mode by atomic oxygen, the radiative damping rate in the region of 90–100 km is ∼1.3 day −1 due to the near-local thermodynamic equilibrium nature of CO2 15-μm band emission. This is comparable to the damping rate induced by eddy and molecular diffusion of ∼2.5 day−1 in the corresponding region. It is also found that the radiative damping of the temperature perturbation in the winter polar mesopause is more than a factor 3 greater than in the summer polar mesopause. A simple and accurate parameterization for the scale-dependent damping rate as a function of altitude for any temperature profile is derived and tested with a zonally averaged model atmosphere. The typical percentage error of such a simple parameterization is about 10%–20%. This parameterization can be used in models of wave-zonal flow interaction in the earth's middle atmosphere.

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