The first rainy season in South China is a unique climate phenomenon. It is hypothesized that the
particular topographic characteristics (e.g. mesocale mountains) give rise to such a phenomenon. 10
years' Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) data such as rainfall
frequency and vertical profile regarding two different kinds of rainfalls (i.e. stratiform and convective
rainfall) are comparatively considered. It is discovered that terrains play an important role in the
determination of the occurrence and intensity of rainfall, even these almost neglected mesoscale
mountains. The above is also confirmed by 6 years' Atmospheric Infrared Sounder (AIRS) temperature
and humidity data.
New satellite observations reveal several distinct features of the South China Sea (SCS) summer climate: an intense
low-level southwesterly wind jet off the coast of south Vietnam, a precipitation band on the western flank of the
north-south running Annam mountain range, and a rainfall shadow to the east in the western SCS off the east coast of
Vietnam. A high-resolution full-physics regional atmospheric model is used to investigate the mechanism for the
formation of SCS summer climate. A comparison of the control model simulation with a sensitivity experiment with the
mountain range artificially removed demonstrates that the aforementioned features form due to orographic effects of the
Annam mountains. Under the prevailing southwesterly monsoon, the mountain range forces the ascending motion on the
windward and subsidence on the lee side, giving rise to bands of active and suppressed convection, respectively. On the
south edge of the mountain range, the southwesterlies are accelerated to form an offshore low-level wind jet. The
mid-summer cooling in the SCS induced by this wind jet further helps reduce precipitation over the central SCS. A
reduced-gravity ocean model is used to investigate the ocean response to the orographically induced wind forcing, which is found to be important for the formation of the double-gyre circulation observed in the summer in SCS, in particular for the northern cyclonic circulation. Thus, orography is a key to shaping the SCS summer climate both in the atmosphere and in the ocean.
The high quality dataset from the South China Sea (SCS) Monsoon Experiment and 40-year NCEP/NCAR reanalysis data are used to investigate the large scale features and abrupt change in meteorological elements during the onset of the SCS summer monsoon. It is found that the SCS summer monsoon establishment is characterized by the South Asian High migrating swiftly from the eastern side of Philippines to the northern part of Indo-China Peninsula and the enhancement of the Bay of Bengal trough and equatorial westerly over the Indian Ocean associated with the equatorial westerly expanding towards northeastward, and followed by the mid-low latitude interaction and continuous retreat eastward of the western Pacific subtropical high. Numerical results reveal that the Indial Peninsula acts as a critical role for the enhancement of the Bay of Bengal trough with a cyclonic difference circulation excited to the east side of the peninsula through ground sensible heating in such a way that the SCS summer monsoon occurs prior to the Indian summer monsoon.