Vertical circulation structure, interannual variation features and variation mechanism of western Pacific subtropical high

The paper investigates the vertical circulation structure of the western Pa cific subtropical high (STH) and its interannual variation features in rela tion to East Asian subtropical summer monsoon and external thermal forcing by using the high-resolution and good-quality observations from the 1998 So uth China Sea Summer Monsoon Experiment (SCSMEX), the NCEP 40-year reanalys is data and relevant SST and the STH parameters. It is found that the verti cal circulation structures differ greatly in features between quasistationa ry and transient components of the western Pacific STH. When rainstorms hap pen in the rainband of East Asian subtropical monsoon on the STH north side . the downdrafts are distinct around the ridge at a related meridian. The s inking at high (low) levels comes from the north (south) side of the STH. t hereby revealing that the high is a tie between tropical and extratropical systems. The analyses of this paper suggest that the latent heat release as sociated with subtropical monsoon precipitation, the offshore SST and East Asian land-sea thermal contrast have a significant effect on the STH intera nnual anomaly. Our numerical experiment shows that the offshore SSTA-caused sensible heating may excite an anomalous anticyclonic circulation on the w est side. which affects the intensity (area) and meridional position of the western Pacific STH.