The role of shallow convection in the water and energy cycles of the atmosphere |
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Authors: | Knut von Salzen Norman A McFarlane Michael Lazare |
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Institution: | (1) Canadian Centre for Climate Modelling and Analysis, Meteorological Service of Canada, University of Victoria, P.O. Box 1700, STN CSC, Victoria, Victoria, BC, V8W 2Y2, Canada |
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Abstract: | The Canadian Centre for Climate Modelling and Analysis atmospheric general circulation model (AGCM4) is used to study the
role of shallow convection in the hydrologic and energy cycles of the atmosphere. Sensitivity tests with AGCM4 show a marked
effect of the parameterization of shallow convection in the model. In particular, including the parameterization of shallow
convection produces considerably enhanced vertical mixing and decreased stratiform cloud amounts in the lower subtropical
atmosphere over the oceans. The differences in simulated stratiform cloud amounts are associated with a change in the globally
averaged outgoing shortwave radiative flux at the top of the atmosphere of about 11 W m−2. Additionally, precipitation rates are considerably reduced for stratiform clouds and enhanced for convective clouds in the
subtropics, if the parameterization of shallow convection is included in the model. Additional tests show that the simulated
responses in cloud amounts and precipitation to the treatment of shallow convection are robust. Additional simulations with
modified closures for deep convection and other changes to the treatment of convection in the model still lead to similar
responses of the model results. |
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