A Study of the Role of Radiational Cooling in a Planetary Boundary Layer

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  • 1 Laboratory for Atmospheric Research, University of Illinois at Urbana-Champaign, Urbana, Ill. 61801
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Abstract

A model based on a detailed treatment for the radiative transfer and a mixing-length treatment for the sensible heat flux is used to investigate whether or not an equilibrium planetary boundary layer would plausibly exist when a surface heat input is counterbalanced by long-wave radiational cooling within the layer associated with a given moisture distribution. It is found that in order to have such a PBL for a representative set of external parameters, the temperature would be excessively low. Thus, an equilibrium PBL resulting from a balance between a convergence of eddy heat flux and a divergence of radiant flux would not likely exist under normal circumstances. However, if the moisture is concentrated in a relatively thin region near the surface, such a PBL may be expected to form. In such a case, there is a nearly adiabatic layer over a superadiabatic layer. The cross-isobar angle is found to increase with the total amount of water vapor and to decrease with increasing surface heat flux. Opposite dependence on these parameters is, found for the surface stress.

Abstract

A model based on a detailed treatment for the radiative transfer and a mixing-length treatment for the sensible heat flux is used to investigate whether or not an equilibrium planetary boundary layer would plausibly exist when a surface heat input is counterbalanced by long-wave radiational cooling within the layer associated with a given moisture distribution. It is found that in order to have such a PBL for a representative set of external parameters, the temperature would be excessively low. Thus, an equilibrium PBL resulting from a balance between a convergence of eddy heat flux and a divergence of radiant flux would not likely exist under normal circumstances. However, if the moisture is concentrated in a relatively thin region near the surface, such a PBL may be expected to form. In such a case, there is a nearly adiabatic layer over a superadiabatic layer. The cross-isobar angle is found to increase with the total amount of water vapor and to decrease with increasing surface heat flux. Opposite dependence on these parameters is, found for the surface stress.

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