Parameterization of Macroscale Transient Heat Transport for Use in a Mean-Motion Model of the General Circulation

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  • 1 National Meteorological Center, ESSA, Washington, D.C.
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Abstract

Recent work on mean-motion models of the general circulation has led to renewed interest in the parameterization (i.e., expression in terms of model-generated average variables) of the horizontal flux of heat in the atmosphere by transient eddies on the scale of cyclones.

A brief review is made of previous work on this subject and some new computations are presented, leading to confirmation of the usual assumption that the cross-isotherm flux of heat can be expressed using the well-known “Austausch coefficient” method. This empirical finding appears to agree with what is expected from the theory of cyclone development.

When considering heat flow over the globe it is necessary to account for the transient flux component parallel, as well as perpendicular, to the mean isotherms. Apparently, no empirical work has yet been done on this subject.

The geographical fields of the parallel component for different seasons of several years were examined in the light of a theoretical study of Welander, which suggests that, in a rotating fluid, there must be a component of heat flux parallel to the thermal wind and proportional to the mean temperature gradient. Appartently, Welander's conclusion (obtained for the case of small-scale turbulence) does not appear to be applicable to macroscale heat transfer on the scale of traveling wave cyclones. Nevertheless, some variants of this concept may lead to a useful parameterization of the parallel flux.

Abstract

Recent work on mean-motion models of the general circulation has led to renewed interest in the parameterization (i.e., expression in terms of model-generated average variables) of the horizontal flux of heat in the atmosphere by transient eddies on the scale of cyclones.

A brief review is made of previous work on this subject and some new computations are presented, leading to confirmation of the usual assumption that the cross-isotherm flux of heat can be expressed using the well-known “Austausch coefficient” method. This empirical finding appears to agree with what is expected from the theory of cyclone development.

When considering heat flow over the globe it is necessary to account for the transient flux component parallel, as well as perpendicular, to the mean isotherms. Apparently, no empirical work has yet been done on this subject.

The geographical fields of the parallel component for different seasons of several years were examined in the light of a theoretical study of Welander, which suggests that, in a rotating fluid, there must be a component of heat flux parallel to the thermal wind and proportional to the mean temperature gradient. Appartently, Welander's conclusion (obtained for the case of small-scale turbulence) does not appear to be applicable to macroscale heat transfer on the scale of traveling wave cyclones. Nevertheless, some variants of this concept may lead to a useful parameterization of the parallel flux.

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