Uncertainties in simulating regional climate of Southern Africa: sensitivity to physical parameterizations using WRF Climate Dynamics

par Julien Crétat, Benjamin Pohl, Yves Richard et Philippe Drobinski

accepté le 21 mars 2011 dans la revue Climate Dynamics.

This study aims at quantifying seasonal biases of regional climate model outputs during southern African summer, against a dense in situ measurement network (daily rain-gauge and surface air temperature records, and 12 h UTC radiosondes), and uncertainties associated with some physical parameterizations. Using the non-hydrostatic Advanced Research Weather Forecast (WRF) laterally forced by ERA40 reanalysis, twenty- seven experiments configured with three schemes of cumulus (CU), planetary boundary layer (PBL) and microphysics (MP), are performed at 35 km horizontal resolution during the core of a summer rainy season (December 1993 to February 1994 season) representative of the South African rainfall climatology. WRF simulates accurately seasonal large-scale rainfall patterns, as well as seasonal gradients of South African rainfall and 2-m temperature, and seasonal vertical profiles of the air temperature and humidity. However seasonal biases fluctuate strongly from an experiment to another, denoting considerable uncertainties generated by physical package. Rainfall amounts are the most sensitive parameter to the tested schemes. Their geography, intensity, and intraseasonal characteristics are predominantly sensitive to CU schemes, and much less to PBL and MP schemes. Some CU-PBL combinations produce additive effects, which can dramatically either reduce or increase biases. Satisfying configurations are found for Southnot have been possible without testing numerous physical parameterizations.

Crétat J, B Pohl, Y Richard & P Drobinski (2011) Uncertainties in simulating regional climate of Southern Africa: sensitivity to physical parameterizations using WRF. Climate Dynamics, published on line. doi:10.1007/s00382-011-1055-8

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Uncertainties in simulating regional climate of Southern Africa: sensitivity to physical parameterizations using WRF Climate Dynamics

par Julien Crétat, Benjamin Pohl, Yves Richard et Philippe Drobinski

accepté le 21 mars 2011 dans la revue Climate Dynamics.

This study aims at quantifying seasonal biases of regional climate model outputs during southern African summer, against a dense in situ measurement network (daily rain-gauge and surface air temperature records, and 12 h UTC radiosondes), and uncertainties associated with some physical parameterizations. Using the non-hydrostatic Advanced Research Weather Forecast (WRF) laterally forced by ERA40 reanalysis, twenty- seven experiments configured with three schemes of cumulus (CU), planetary boundary layer (PBL) and microphysics (MP), are performed at 35 km horizontal resolution during the core of a summer rainy season (December 1993 to February 1994 season) representative of the South African rainfall climatology. WRF simulates accurately seasonal large-scale rainfall patterns, as well as seasonal gradients of South African rainfall and 2-m temperature, and seasonal vertical profiles of the air temperature and humidity. However seasonal biases fluctuate strongly from an experiment to another, denoting considerable uncertainties generated by physical package. Rainfall amounts are the most sensitive parameter to the tested schemes. Their geography, intensity, and intraseasonal characteristics are predominantly sensitive to CU schemes, and much less to PBL and MP schemes. Some CU-PBL combinations produce additive effects, which can dramatically either reduce or increase biases. Satisfying configurations are found for Southnot have been possible without testing numerous physical parameterizations.

Crétat J, B Pohl, Y Richard & P Drobinski (2011) Uncertainties in simulating regional climate of Southern Africa: sensitivity to physical parameterizations using WRF. Climate Dynamics, published on line. doi:10.1007/s00382-011-1055-8