The western Pacific subtropical high after the 1970s: westward or eastward shift?

The interdecadal variation of the western Pacific subtropical high (WPSH) in summer (June–July–August) during 1979–2009 relative to 1948–1978 was investigated based upon NCEP–NCAR reanalysis data. Since the WPSH appeared to be much more stable and stronger in the lower troposphere compared to the middle troposphere and had great influences on the East Asian summer climate with the lower-level southerlies or southwesterlies at its western and southern edge, the interdecadal changes of the WPSH at low levels were examined in this study. Over the area of interest (~15°–30°N, 120°–150°E), the 850-hPa anticyclone circulation was weakened, the sea level pressure decreased, the relative vorticity at middle and lower levels (1,000–600 hPa) increased, and the maximum meridional wind at each latitude (between 17.5° and 32.5°N) moved eastward. All the above decadal variations suggested that the WPSH recessed eastward during 1979–2009 relative to 1948–1978, which can be displayed in the 850-hPa eddy geopotential height field. In association with the eastward recession of the WPSH, the water vapor transport from the Indian summer monsoon played a more important role in the summer precipitation over the middle and lower reaches of the Yangtze River valley during 1979–2009 relative to 1948–1978.