Radiative/Turbulent Transfer Interactions in Layer Clouds

Howard P. Hanson Cooperative Institute for Research in Environmental Sciences, University of Colorado/NOAA, Boulder, CO 80309

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Abstract

The differential absorption and emission of radiation with height inside clouds creates sources and sinks of buoyancy and thus can be an important factor in the turbulence-maintaining and dissipating processes of the clouds. This paper is concerned with the roles that solar and infrared radiation play in the turbulence budget of layer clouds, with primary emphasis on marine stratocumulus and inferential discussion of other layer cloud systems.

Physically realistic parameterizations of solar and infrared (IR) fluxes are used to show how the turbulence generation by cloud-top IR cooling can be more than offset by stabilization due to absorption of sunlight, and how the role of cloud-base IR warming depends crucially on the height of the cloud base. In the context of a mixed-layer model, these effects can be cast entirely in terms of the height of the layer's center of mass relative to the net heating and/or cooling due to the radiative transfer. Implications for the diurnal cycle and for a thin-cloud instability are discussed.

Abstract

The differential absorption and emission of radiation with height inside clouds creates sources and sinks of buoyancy and thus can be an important factor in the turbulence-maintaining and dissipating processes of the clouds. This paper is concerned with the roles that solar and infrared radiation play in the turbulence budget of layer clouds, with primary emphasis on marine stratocumulus and inferential discussion of other layer cloud systems.

Physically realistic parameterizations of solar and infrared (IR) fluxes are used to show how the turbulence generation by cloud-top IR cooling can be more than offset by stabilization due to absorption of sunlight, and how the role of cloud-base IR warming depends crucially on the height of the cloud base. In the context of a mixed-layer model, these effects can be cast entirely in terms of the height of the layer's center of mass relative to the net heating and/or cooling due to the radiative transfer. Implications for the diurnal cycle and for a thin-cloud instability are discussed.

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