APPLICATION OF A NEW DOWNSCALING MODEL TO MONTHLY PRECIPITATION FORECAST

A relationship between monthly mean precipitation and monthly mean circulation represented by 500 hPa geo-potential height was given to combine dynamical and statistical approaches. The physical explanations of monthly mean circulation and precipitation were also presented. Statistical weights of each item of the relationship (the downscaling model) were derived from the monthly NCEP/NCAR reanalysis data (500 hPa) and China's observed precipitation data during the control period from January of 1951 to December of 1991. The hindcast test was conducted using those data from January of 1992 to December of 2001. The test indicates that the method (new model) has a high score skill for monthly mean precipitation forecast. Comparison of monthly forecast of precipitation amounts between the issued operational forecast and the new model using the 500 hPa height forecast obtained from T63/NCC GCM from January to June 2002 shows that the new model forecast has a higher score than the issued operational forecast result.