Contrast analysis of a heavy rain at the end of the first rainy season in 2010 in west and east of South China

A heavy rain took place at the end of the first rainy season of 2010 in the South China,and this process in the west was different from that in the east. By applying the NCEP reanalysis data,conventional observation data,characteristics and mechanisms of the heavy rain were analyzed. The results showthat as a whole,main influencing system at high levels over the Southern China is a weak ridge stretching southeast from South Asia High,and the air flowthere is divergent. M iddle level ridge stretching westward from Subtropical High retreats eastward firstly,and then moves westward. Once boundary layer jet forms,the heavy rain appears in the south of equivalent potential temperature front at lowlevel,and stream convergence takes place. For different divisions,the heavy rain occurs at many stations simultaneously twice in the west of South China,and it lasts 1 day every time. Averaged indexes calculated using the radiosonde stations data showthat 850 h Pa equivalent potential temperature and precipitable water vapor are large,and stratification in the middle and lowlevels is very unstable before the number of stations with the heavy rain increases significantly in the west. Boundary layer jet weakens obviously twice over the west of South China between the two days when heavy rain takes place at many stations simultaneously. Between the two days of multiple heavy rain sites in the west,both upward movement and water vapor convergence in lowlevel is interrupted obviously. It is only one time for the heavy rain event of many stations simultaneously in the east of South China,while it lasts for 3 days. The 3 indexes mentioned above are all not very favorable for the increase of number of heavy rain stations,although boundary layer jet maintains over the east of South China during the three days,and water vapor convergence and upward motion at lowlevel are not interrupted. Thus this precipitation in the east is characterized with large areas,strong intensity and long duration. Generation or disappearance of southerly boundary layer jet and horizontal scale are crucial to heavy rain in the first rainy season in the South China.