The North Pacific Subtropical High in August in Twentieth-Century CMIP3 Multimodal Dataset

Abstract

We investigated the climatological shape of the North Pacific subtropical high (NPSH) and its interannual and submonthly variability (variability with a period of less than 31 days) in August during the twentieth-century using the Coupled Model Intercomparison Project phase 3 (CMIP3) multimodel dataset. The climatological NPSH in a CMIP3 multimodel ensemble mean (MMEM) is similar to that in the real atmosphere. However, intermodel differences of the NPSH are quite large in the southwestern North Pacific where some models simulate stronger NPSH with positive geopotential height (Z) anomalies, and other models simulate weaker NPSH with negative anomalies compared with the MMEM NPSH. An NPSH index was defined as the deviation of the climatological Z (Z) in each model from the MMEM Z, averaged over the region 123.75°–151.25°E, 16.25°–31.25°N at 850 hPa. Composite analyses using data from the four most positive (P-type) and negative (N-type) models revealed that the Indian monsoon westerly is weaker, precipitation to the east of the Philippines is smaller, and the sea surface temperature (SST) to the west of the warm pool is greater in the P-type than in the N-type models. We suggest that better simulation of the east–west gradient of the SST around the warm pool is related to improved simulation of the climatological NPSH in the southwestern North Pacific. Models with positive (negative) values of the NPSH index tend to simulate small (large) interannual and submonthly variability in the index area.