Numerical Simulation And Diagnostic Analysis Of BILIS Typhoon Heavy Rainfall In 2006

The torrential rain during July 14 to 16 of 2006 at South Chian causeing by alanding typhoon (NO.0604, BILIS) is studied in the paper. It is revealed that longlasting of the Mid-latitude high pressure and the southwest musoon is the favorativeenvironmental conditions for heavy rainfall. The vapor divergence, wind field andthe thermal field etc. of typhoon are asymmetric. The center of positive vapordivergence locates on the south of typhoon is more stronger than that locates on thenorth of typhoon.A strong convergent region in low level of troposphere and a strongdivergence region in high level of troposphere are locate on the south of typhoon.Strong ascending area lacates on the south of typhoon about 200km.The meso-scale numerical model MM5 is used to simulate the heavy rainprocess. Using the model output with high spatial and temporal resolution, we studythe characteristic and mechanism of the rainfall in south of Hulan and north ofGuangdong in more detail.It turns out that the distributing and evolution of heticity and vapor-lelicity is aindicator of typhoon heavy rainstorm in a certain sense. The change of vapor-helicity can reflect the movement and development of synoptic system and theposition and intensity of the rainstorm. Through analyzing PV and MPV during theheavy rainstorm process, it is showed that is wet symmetry instability aboverainstorm area and unnormal high PV make the rainfall. The center of rainfall locateson near ascending Q-vector divergence.Secondary circulation is mainly dued to thedifference between vertical and horizontal shear .Diabatic precess forcing is alsoattributed to secondary circulation.Meso-scale terrain affects obviously the location and intensity of precipitationcell. The effect caused by the variation of initial humidity field on simulation ofrainfall area is different from region.The amount of water vapor which is necessaryfor the formation of precipitation in some place where short of water vaportransportation is determined by the initial field, but that of another place whereabundant of water vapor transportation isn't so.