Characteristics of Precipitation in the Meiyu-Baiu Season in the CMIP3 20th Century Climate Simulations

Characteristics of precipitation in the Meiyu-Baiu season in twenty-two 20th century climate simulations contributed to the World Climate Research Programme's Coupled Model Intercomparison Project phase 3 (CMIP3) are studied comparing with two observed precipitation data. The distribution of precipitation in the Meiyu-Baiu season is characterized by the narrow Meiyu and Baiu frontal precipitation zone (MFZ and BFZ) extending along the northern rim of the North Pacific Subtropical anticyclone (NPSA), the maximum precipitation zone (S. Max zone) along the southern rim of the NPSA, and the minimum precipitation zone (S. Min zone) to the south of MFZ and BFZ. The latitude of these zones and the precipitation within these zones produced by the models are examined, using the 20-year (1980-1999) averaged values for May, June and July. The precipitation in these zones in each month obtained from the respective many-model ensemble average (MEA) coincides approximately with the observation data, except the western "S. Max zone" in May. However, the MEA simulates MFZ, BFZ and "S. Min zone" to the north of their observed latitude in May. MEA reasonably reproduce the latitude of both MFZ and BFZ for June, and the latitude of BFZ and "S. Min zone" for July. The latitude of the "S. Max zone" is approximately reproduced for MJJ. The standard deviation (STD) of the precipitation from the MEA does not change widely from zone to zone and from month to month. However, STD or the latitude of zones varies widely. The STD of the latitude of MFZ and BFZ became larger in June and July. The STD of the latitude of MFZ is larger than that of BFZ. The STD of the latitude for "S. Max zone" is especially large. The models show large deviation from the MEA around the western and southern rim of the NPSA. Low horizontal resolution models tend to yield the larger deviation, in regard to both the latitude and precipitation, as compared with models of medium resolution. However, a few high resolution models still produce large deviation from the MEA. It is hard to state conclusively the influence of the cumulus parameterization scheme on the intense precipitation zones.