Sensitivity of Tropical Convection to Land Surface Processes

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  • 1 Laboratoire de Météorologie Dynamique du CNRS, Ecole Normale Supérieure, Paris, France
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Abstract

This paper studies the sensitivity of large-scale tropical convection to land surface changes in the general circulation model of the LMD. Ale method of analysis is based on a conceptual model of the energetics of convection applied every day of the simulation to the grid points within the region of interest. The synoptic events are then classified by their potential energy divergence. This allows for the distinction between the frequency and the characteristic energy and water cycle of the events. The difference in precipitation found in the tropical deforestation experiments is explained by changes in the number of intense convective events while their characteristic precipitation remains largely unchanged. With a series of ten deforestation experiments the relation between land surface processes changes and variations of the frequency of convection is studied. The highest sensitivity is found for the sensible heat flux: its increase leads to more deep convective events. The reduction of evaporation associated with deforestation decreases precipitation only for subsident events but it is only of marginal importance for the regional rainfall. These results suggest a relatively simple mechanism for the sensitivity of tropical convection to land surface processes in our model.

Abstract

This paper studies the sensitivity of large-scale tropical convection to land surface changes in the general circulation model of the LMD. Ale method of analysis is based on a conceptual model of the energetics of convection applied every day of the simulation to the grid points within the region of interest. The synoptic events are then classified by their potential energy divergence. This allows for the distinction between the frequency and the characteristic energy and water cycle of the events. The difference in precipitation found in the tropical deforestation experiments is explained by changes in the number of intense convective events while their characteristic precipitation remains largely unchanged. With a series of ten deforestation experiments the relation between land surface processes changes and variations of the frequency of convection is studied. The highest sensitivity is found for the sensible heat flux: its increase leads to more deep convective events. The reduction of evaporation associated with deforestation decreases precipitation only for subsident events but it is only of marginal importance for the regional rainfall. These results suggest a relatively simple mechanism for the sensitivity of tropical convection to land surface processes in our model.

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