An Accurate Radiative Heating and Cooling Algorithm for Use in a Dynamical Model of the Middle Atmosphere

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  • 1 Department of Atmospheric Sciences, University of Washington, Seattle 98195
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Abstract

An infrared radiative heating and cooling algorithm designed to be used with dynamical models of the middle atmosphere is described. A Curtis matrix is used to compute cooling by the 15 and 10 μm bands of carbon dioxide. Escape of radiation to space and exchange with the lower boundary are used for the 9.6 μm band of ozone. Voigt line shape, vibrational relaxation, line overlap, and the temperature dependence of line strength distributions and transmission functions are incorporated into the CO2 Curtis matrices. Radiative damping rates derived from this algorithm give a damping rate of ∼0.5 day−1 for temperature disturbances in the mesosphere of vertical extent 25 km. When this algorithm is employed in the dynamical model of Hotton and Wehrbein (1980) to calculate the zonal mean circulation of the middle atmosphere, the zonal and meridional circulations generated are nearly twice as strong as those generated in the model of Holten and Wehrbein (1980) which used a Newtonian cooling algorithm based on the radiation-to-space approximation of Dickinson (1973). Since the zonal circulation calculated with the new radiative algorithm is also much stronger than that observed, this result supports the assertion that there is a very efficient, but as yet obscure, mechanical damping mechanism in the mesosphere.

Abstract

An infrared radiative heating and cooling algorithm designed to be used with dynamical models of the middle atmosphere is described. A Curtis matrix is used to compute cooling by the 15 and 10 μm bands of carbon dioxide. Escape of radiation to space and exchange with the lower boundary are used for the 9.6 μm band of ozone. Voigt line shape, vibrational relaxation, line overlap, and the temperature dependence of line strength distributions and transmission functions are incorporated into the CO2 Curtis matrices. Radiative damping rates derived from this algorithm give a damping rate of ∼0.5 day−1 for temperature disturbances in the mesosphere of vertical extent 25 km. When this algorithm is employed in the dynamical model of Hotton and Wehrbein (1980) to calculate the zonal mean circulation of the middle atmosphere, the zonal and meridional circulations generated are nearly twice as strong as those generated in the model of Holten and Wehrbein (1980) which used a Newtonian cooling algorithm based on the radiation-to-space approximation of Dickinson (1973). Since the zonal circulation calculated with the new radiative algorithm is also much stronger than that observed, this result supports the assertion that there is a very efficient, but as yet obscure, mechanical damping mechanism in the mesosphere.

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