The Formation Mechanism Analysis of Continuity Strong Precipitation at the Middle East Area of China in July 2012

Using the NCEP/NCAR reanalysis data,the temporal and spatial variation features of the leading members of the East Asian summer monsoon system during the durative heavy precipitation at the middle east area of China in mid-July 2012 was analyzed. The results showed that,the position of North boundary of subtropical high,the south ridge line and the midlatitude frontal zone were relatively stable during the persistent heavy rainfall. Middle and lower reaches of the Yangtze River has been in the divergence zone of the northerly wind of the South and the southerly wind of the trough. When the subtropical high moving southwrad,the heavy precipitation often occured the north of the584 line; while the subtropical high moving northwrad,the heavy precipitation often occured the south of the 584 dagpm line. Before the persistent heavy rainfall occured,the atmosphere was unstable stratification. The cold air of westerly trough frequently carried and the warm air of the Southwest Jet at low altitude repeatedly carried,which the strong wind speed gradient of the left of exit region has provided the impetus for the development of storm conditions. The intrusion of dry air at low-level,the front and back vertical circulation of the trough and the Vortex maintained the upward vertical movement,and the persistent heavy rainfall had developed. Upper-level westerly jet strengthened( weakened)before Southwest Jet at low altitude to strengthened( weakened) for 2- 5 d,that had a ahead of significance for durative heavy precipitation.