Variation Of The West Pacific Subtropical High And Its Possible Causes Under The Background Of Climate Warming

Using the subtropical high index data from the National Climate Center, NCEP/ NCAR reanalysis data and the NOAA sea surface temperature data, based on the gaussian filter, moving average and the methods of correlation and synthesis analysis, the West Pacific subtropical high (WPSH) and possible reasons for its variation under the background of climate fluctuation of cold or warm are discussed in this study.Analysis shows that as the climate fluxing in recent 60 years, the most significant change of WPSH is the expanding of the area. At the same time, the intensity of WPSH has intensified and the west ridge point has extended westward, while the southern boundary has expanded. The interannual variability of every WPSH index has increased. The intensity of WPSH has intensified in the late 1980s, the west ridge point has extended westward in the early 1990s. The ridge line has expressed the wave of north-south-north. As the climate warming, the west ridge point extending later, maintain longer and magnitude larger. The layers of WPSH morphological changes are very different between before and after the climate waring. The shape of WPSH has begun to extend westward, expand southward on the 850-700hPa, the most significant morphological differences appeared until the 500hPa.In the climate warmer period, the east-west temperature gradient has reduced but the north-south temperature gradient has increased of the Pacific sea surface temperature(SST),resulting in the strengthening and southward shift of Hadley circulation. The Tropical Indian SST has being increasing, resulting in weakening of the Walker circulation in the Tropical Indian-the west Pacific, weakening the rising branch in the nearby west Pacific. The Australian High and the Mascarene High has increased, the South China Sea, the Philippines, Somalia cross-equatorial flow has enhanced in the early September to October, the northeasterly flow on the south side of WPSH has strengthened, the South Asia High has significantly enhanced and developed. Thereby the characteristics of summer WPSH has showed strengthened, expanded, the west ridge point extended westward and the southern boundary expanded southward.The layers of WPSH morphological difference in the cool and warm period are corresponding with the atmospheric heat source and vorticity around the WPSH. As the climate warming, the atmospheric heat source on the west and south side of WPSH has begun to significant strengthen on the 850-700hPa and the most obvious heating appeared 500hPa. The center of heating source on 500hPa has moved south; The anticyclonic vorticity on the west and south side of WPSH has increased from low to high level of troposphere. The anticyclonic vorticity on the west side of WPSH has significant increased on the 850-700hPa and the anticyclonic vorticity center on the south has moving southward, the most obvious increased appeared 500hPa. In the climate warmer period, the heating on the west, south and key area of WPSH has strengthened, resulting in the increasing of anticyclonic vorticity in the same area, so the WPSH has developed to the increasing of anticyclonic vorticity. Explaning that the change of atmospheric heat source could resout the variety of vorticity, leading to the west ridge point extend westward, the southern boundary expand southward and the whole WPSH moved southward.