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The timing of the South Asian High (SAH) establishment over the Indochina Peninsula (IP) from April to May and its relations to the setup of the subsequent tropical Asian summer monsoon and precipitation over eastern-central China in summer are investigated by using NCEP/NCAR daily reanalysis data, outgoing longwave radiation (OLR) data and the daily precipitation data from 753 weather stations in China. It is found that the transitions of the zonal wind vertical shear and convection establishment over tropical Asia are earlier (later) in the years of early (late) establishment of SAH. In the lower troposphere, anti-cyclonic (cyclonic) anomaly circulation dominates the equatorial Indian Ocean. Correspondingly, the tropical Asian summer monsoon establishes earlier (later). Furthermore, the atmospheric circulation and the water vapor transport in the years of advanced SAH establishment are significantly different from the delayed years in Asia in summer. Out-of-phase distribution of precipitation in eastern-central China will appear with a weak (strong) SAH and western Pacific subtropical high, strong (weak) ascending motion in the area south of Yangtze River but weak (strong) ascending motion in the area north of it, and cyclonic (anti-cyclonic) water vapor flux anomaly circulation from the eastern-central China to western Pacific. Accordingly, the timing of the SAH establishment at the upper levels of IP is indicative of the subsequent onset of the tropical Asian summer monsoon and the flood-drought pattern over eastern-central China in summer. [ABSTRACT FROM AUTHOR]

Comparative analysis is carried out by using finite-domain power spectrum and lagged regression methods for the propagating characteristics and air-sea interaction processes of intraseasonal oscillations (ISOs) in the Asia to western Pacific (AWP) region during the boreal summer between the active and inactive tropical cyclone (TC) years from 1979 to 2004. The results show as follows. (1) There exist more significant eastward propagating characteristics of the ISO in the active TC years over the whole AWP region. The ISOs of convection propagate zonally with more eastward extension in the years with active tropical cyclone activities, during which the 20-60-day period is strengthened, western Pacific becomes an area with evident characteristics of the propagation that is closely related to TC activities. (2) The air-sea interaction processes are the same in both active and inactive TC years, and the energy exchanges between the air and the sea play a role in maintaining the northwestward propagation of ISOs. (3) The air-sea interaction is more intensive in the active TC years than in the inactive ones. It is particularly true for the latent heat release by condensation as the result of convection, which may be one of the reasons resulting in significant differences in characteristics of ISOs between the active and inactive TC years. [ABSTRACT FROM AUTHOR]