Features of the large-scale circulation of the extremely heavy rain with severe floods over South China in June 2005 and its possible cause

摘要

Based on NCAR/NCEP daily reanalysis, a study is performed of the circulation background for the South-China torrential rains leading to flash floods in June 2005 with the possible causes explored. Results show that a weak El Nino episode in 2004-2005 is the climate background of the flooding. Compared to the situation of the summer 2005, thernapparent heat source and the apparent vapor sink are anomalously intense in the rainy period June 17～26rnover the study region, with their high-value belts resembling the rainfall distribution and their centers roughly coincident with the rainfall cores. The anomalous heating source from the eastern coast of the Arabian Sea to the Bay of Bengal excites a high-level abnormal anticyclone to the northwest, making the south-Asian high intensified and westward of normal, during which China mainland is under the effect of an anomalous cyclonic circulation that keeps the south-Asian high from northward displacement, allowing it to stay in the south of the Tibetan plateau - South China, a situation that South China is situated in the rising area on the south side of upper-air westerly jets, making for the occurrence and maintenance of the intense rains, resulting in extensive flooding.