Interannual Variability Of The South-Asian High Establishment Over The Indo-China Peninsula From April To May: Data Analysis And Numerical Simulation

Interannual variability of the South-Asian High (SAH) establishment over the Indo-China peninsula (ICP) from April to May is investigated using NCEP/NCAR reanalysis data, out-going longwave radiation (OLR) data and the daily rain data of753stations of China. The possible causes of interannual variability differences and its relation to southern Asian summer monsoon and precipitation over East-Central China are discussed. Finally, the mechanism of the SAH establishment processes over the ICP is studied by RegCM3model. The main results are as follows:(1)Interannual variability of the SAH establishment over the ICP from April to May are as follows:In the upper troposphere, interannual variability differences mainly reflected in the development of two circulation center. Before the SAH establishment, the center of the anti-cyclone to the east of the Philippines moves fast in the early years. But in the delayed years, there isn’t a closed anti-cyclone over the western Pacific. The upper tropospheric anti-cyclone over the ICP is stronger and wider (weaker and narrower) in the early (delayed) years. The duration of the SAH establishment is relatively long (short) in the early (delayed)-establishment years. Then the time of the SAH establishment is closely associated with divergent movement of upper tropospheric over the the southeast Bay of Bengal (BOB)-ICP and the southern South China Sea. The earlier (later) divergent movement flourish is corresponding to the earlier (later) SAH establishment.In the lower troposphere, both wind and Sea level pressure fields show reverse distribution situation. And the intensity of Walker circulation has also the differences: Walker circulation is stronger (weaker) in the early (delayed) years.(2)The establishment time of the center of the anti-cyclone over the ICP is closely associated with the convective development over this region. The earlier (later) convective flourish is corresponding to the earlier (later) center establishment.(3)The moving westward velocity and intensity of the anti-cyclonic center to the east of the Philippines are affected by vertical motion and atmospheric diabatic heating. After the anti-cyclonic center to the east of the Philippines moves to130°-145°E, diabatic heating vertical change plays a major role in its maintenance. Diabatic heating vertical change to the east of the Philippines affected by the intensity of Walker circulation can give rise to the interannual variation of the SAH establishment.(4)The earlier (later) SAH establishment is followed by the earlier (later) onset of the BOB-ICP summer monsoon and the South China Sea summer monsoon. The pattern of flood-drought over East-Central China in Summer in early-establishment years is different from the delayed years. Accordingly, the time of the SAH establishment over the ICP plays an indicative role in the subsequent onset of the southern Asian summer monsoon and distribution of the precipitation of East-Central China in Summer.(5)Accord to numerical simulation, it is found that the SAH establishment over the ICP is notablely affected by the change of atmospheric heating field over the ICP. This simulation verifies the result that the SAH establishment over the ICP from April to May is affected by atmospheric thermal effect, especially diabatic heating.