Meteorological Process of "7·17" Heavy Rain Event of 2007 in Xinjiang

A heavy rain event occurred in Xinjiang during the period from July 13 to 17 in 2007.The circulation situation,moisture transfer,helicity fields etc were analyzed to open out the water vapor sources and driving force of such a heavy rain by use of NCEP reanalysis Data(horizontal resolution 1°×1 °) and the conventional ground observational data.The results show that:(1) The stable large-scale circulation,binary distribution of the South Asian high-pressure,north-south oscillation of Iran's subtropical high-pressure,stretching of Western Pacific subtropical high-pressure into the Northwest,and long time keeping of Central Asia vortex are the circulation background and weather conditions of the heavy rain process.(2) Moisture comes mainly from the bay of Bengal and westerly circulation during the heavy rain event.(3) Total moisture input during the heavy rain event is 517.99×108 t,and total moisture output is 353.76×108 t,so net moisture budget is 164.23×108 t.The western boundary contributes the most moisture input of 190.06×108 t,and southern boundary input water vapor 104.1×108 t and northern boundary input water vapor 100.07×108 t,and east boundary is the main boundary of moisture output of 230.00×108 t.(4) Helicity is a physical parameter on behalf of atmospheric rotation and movement direction along the rotation axis,so helicity and thermal parameters can be a combined to analyze and forecast heavy rain weathers.