Reduction of systematic biases in regional climate downscaling through ensemble forcing |
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Authors: | Hongwei Yang Bin Wang Bin Wang |
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Institution: | 1. LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China 2. Department of Meteorology, University of Hawaii at Manoa, Honolulu, Hawaii 3. International Pacific Research Center, University of Hawaii at Manoa, Honolulu, Hawaii 4. LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
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Abstract: | Simulations of the East Asian summer monsoon for the period of 1979–2001 were carried out using the Weather Research and Forecast (WRF) model forced by three reanalysis datasets (NCEP-R2, ERA-40, and JRA-25). The experiments forced by different reanalysis data exhibited remarkable differences, primarily caused by uncertainties in the lateral boundary (LB) moisture fluxes over the Bay of Bengal and the Philippine Sea. The climatological mean water vapor convergence into the model domain computed from ERA-40 was about 24% higher than that from the NCEP-R2 reanalysis. We demonstrate that using the ensemble mean of NCEP-R2, ERA-40, and JRA-25 as LB forcing considerably reduced the biases in the model simulation. The use of ensemble forcing improved the performance in simulated mean circulation and precipitation, inter-annual variation in seasonal precipitation, and daily precipitation. The model simulated precipitation was superior to that in the reanalysis in both climatology and year-to-year variations, indicating the added value of dynamic downscaling. The results suggest that models having better performance under one set of LB forcing might worsen when another set of reanalysis data is used as LB forcing. Use of ensemble mean LB forcing for assessing regional climate model performance is recommended. |
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