A Numerical Simulation of Seasonal Stratospheric Climate: Part II. Energetics

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  • 1 Joint Institute for Acoustic and Flight Science, George Washington University - NASA Langley Research Center, Hampton, Va. 23665
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Abstract

Two numerical experiments previously described by Ramanathan and Grose (1978) have been performed to test the climatological response of a three-dimensional stratospheric circulation model over an entire annual cycle to two different longwave radiation schemes in the stratosphere: 1) Experiment 1, a detailed radiative transfer model, and 2) Experiment 2, a simple Newtonian cooling (or heating) model. The energetics of these two experiments are analyzed in this study. It is found that the eddy energy variables-eddy kinetic energy KE; eddy available potential energy AE, the generation of AE, G(AE); and vertical propagation of eddy geopotential energy VE)-exhibit annual variations with maximum values in winter and minima in summer. On the other hand, the zonal energy variables-zonal kinetic energy KZ; zonal available potential energy AZ; and generation of AZ, G(AZ)-undergo semiannual variations with major maximum values in winter, minor maxima in summer and minimum values in spring and fall. Analysis of the energy cycle shows that VE) is the primary energy source for energetics in the lower stratosphere, while VE) and G(AZ) are the energy sources for energetics in the upper stratosphere. The seasonal variations of eddy energy variables are under the control of VE), while those of the zonal energy variables are vitally affected by the latitudinally differential diabatic heating, especially in the summer upper stratosphere.

The comparison study reveals clearly that the experiment that employes the detailed radiation model has significantly larger eddy kinetic energy and eddy available potential energy on the annual mean. Detailed analysis of the two experiments indicates the several ways in which the longwave radiation processes may affect the stratospheric energetics: 1) the temperature dependence of the Newtonian cooling coefficient h causes an increase of G(AZ) and enhances the seasonal variation of G(AZ) in the upper stratosphere; 2) the temperature dependence of h also augments the transmissivity of winter and spring season upper stratosphere to propagating planetary waves; and 3) the exchange of radiative energy between the troposphere and lower stratosphere alters the zonal wind profile during the winter season. The altered zonal wind profile facilitates the propagation of planetary waves within the lower stratosphere. Due to points 2) and 3) above, the magnitudes of eddy energies are much larger in Experiment 1, which employs the detailed radiation model.

Abstract

Two numerical experiments previously described by Ramanathan and Grose (1978) have been performed to test the climatological response of a three-dimensional stratospheric circulation model over an entire annual cycle to two different longwave radiation schemes in the stratosphere: 1) Experiment 1, a detailed radiative transfer model, and 2) Experiment 2, a simple Newtonian cooling (or heating) model. The energetics of these two experiments are analyzed in this study. It is found that the eddy energy variables-eddy kinetic energy KE; eddy available potential energy AE, the generation of AE, G(AE); and vertical propagation of eddy geopotential energy VE)-exhibit annual variations with maximum values in winter and minima in summer. On the other hand, the zonal energy variables-zonal kinetic energy KZ; zonal available potential energy AZ; and generation of AZ, G(AZ)-undergo semiannual variations with major maximum values in winter, minor maxima in summer and minimum values in spring and fall. Analysis of the energy cycle shows that VE) is the primary energy source for energetics in the lower stratosphere, while VE) and G(AZ) are the energy sources for energetics in the upper stratosphere. The seasonal variations of eddy energy variables are under the control of VE), while those of the zonal energy variables are vitally affected by the latitudinally differential diabatic heating, especially in the summer upper stratosphere.

The comparison study reveals clearly that the experiment that employes the detailed radiation model has significantly larger eddy kinetic energy and eddy available potential energy on the annual mean. Detailed analysis of the two experiments indicates the several ways in which the longwave radiation processes may affect the stratospheric energetics: 1) the temperature dependence of the Newtonian cooling coefficient h causes an increase of G(AZ) and enhances the seasonal variation of G(AZ) in the upper stratosphere; 2) the temperature dependence of h also augments the transmissivity of winter and spring season upper stratosphere to propagating planetary waves; and 3) the exchange of radiative energy between the troposphere and lower stratosphere alters the zonal wind profile during the winter season. The altered zonal wind profile facilitates the propagation of planetary waves within the lower stratosphere. Due to points 2) and 3) above, the magnitudes of eddy energies are much larger in Experiment 1, which employs the detailed radiation model.

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