Analysis of the Water Vapor Condition and Vertical Helicity on the Torrential Rain in 1--2, August 2011 in Henan

doi:10.3969/j.issn.1673-7148.2012.02.010

Abstract：Using the conventional data and NCEP reanalysis data in Henan on 1--2, August 2011, the paper analyzed the circulation situation, water vapor condition and vertical helicity of the torrential rain. The results showed that： the moving to the northeast nearly to Henan by the southwest vortex is the typical effects. The plateau trough at 500 hPa moves toward to the east, subtropical anticyclone becomes weaker and then stronger, the southwest vortex in the middle-low level moves along with shear line to the northeast. Henan lies in the front and the front left side of southwest low-level jet export, which provide an advantageous dynamic and water vapor condition to the torrential rain event. The water vapor transport at 700 hPa has a very important indication in this rainfall area. The torrential area in southwestern Henan is near the maximal value of vapor flux and in the front of density gradient with it. The torrential area in central and eastern Henan is in the north of density gradient with vapor flux and the left of the direction of its maximal value＇ s movement. The change of vapor flux divergence at 850 hPa and the begin and strength of the rain have more correlation. The vapor flux divergence turns to convergence, and the convergence layer becomes heavy is the symbol of starting of torrential rain, the sudden enlargement of vapor flux divergence meaning the enlargement of the Strength of the rain. The rapidly increasing of vertical helicity at 700 hPa is corresponded to the rain happen time ; the heavy precipitation occurred in the southeast of the vertical helicity maximal value axis.