A Water Vapor-Energy Balance Model Designed for Sensitivity Testing of Climatic Feedback Processes

Robert G. Gallimore Center for Climatic Research and Department of Meteorology, University of Wisconsin, Madison 53706

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Abstract

A zonal mean water vapor-energy balance (WEB) model is formulated to assess feedback interactions of the hydrologic cycle and lapse rate with the radiative fluxes, snow-dependent albedo and transport mechanisms. The WEB model is designed for comparative study and integration of many sensitivity experiments in which changes in feedback processes are introduced through variation in parameters and/or parameterizations.

Specific processes in the model include 1) an explicit hydrologic cycle with the predicted atmospheric water vapor used in the determination of the solar and longwave fluxes; 2) a land albedo and surface energy budget dependency on explicit model calculations of snowfall, snow melt and snow accumulation; 3) a lapse rate dependency for the longwave emission, sensible heating and mean energy transport; and 4) separate specification for mean and eddy energy and water vapor transports.

The sensitivity of the model energy and water vapor budgets is similar to that obtained in a GCM by Wetherald and Manabe (1975), with several of the more important ones for reduced solar constant being 1) the nonlinear decrease of temperature resulting in part from the rapid intrusion of snowfall into the middle latitude precipitation belt; 2) the large reduction of atmospheric latent enemy content and decreased intensity of the hydrologic cycle; and 3) the nearly invariant total atmospheric energy transport. Based on the similarity of the WEB model and GCM results, a forthcoming paper will examine the parameterizations governing interaction of the model radiative and transport terms with the ice-albedo mechanism.

Abstract

A zonal mean water vapor-energy balance (WEB) model is formulated to assess feedback interactions of the hydrologic cycle and lapse rate with the radiative fluxes, snow-dependent albedo and transport mechanisms. The WEB model is designed for comparative study and integration of many sensitivity experiments in which changes in feedback processes are introduced through variation in parameters and/or parameterizations.

Specific processes in the model include 1) an explicit hydrologic cycle with the predicted atmospheric water vapor used in the determination of the solar and longwave fluxes; 2) a land albedo and surface energy budget dependency on explicit model calculations of snowfall, snow melt and snow accumulation; 3) a lapse rate dependency for the longwave emission, sensible heating and mean energy transport; and 4) separate specification for mean and eddy energy and water vapor transports.

The sensitivity of the model energy and water vapor budgets is similar to that obtained in a GCM by Wetherald and Manabe (1975), with several of the more important ones for reduced solar constant being 1) the nonlinear decrease of temperature resulting in part from the rapid intrusion of snowfall into the middle latitude precipitation belt; 2) the large reduction of atmospheric latent enemy content and decreased intensity of the hydrologic cycle; and 3) the nearly invariant total atmospheric energy transport. Based on the similarity of the WEB model and GCM results, a forthcoming paper will examine the parameterizations governing interaction of the model radiative and transport terms with the ice-albedo mechanism.

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