The Analysis Of The Structure & Characteristic Of Spiral Rain Bands Around The Landing Of Typhoon "HaiTang"

Through the analysis of the weather circulations,we know that West Pacific subtropicalhigh mainly depends on the movement of the Typhoon "Hai Tang" during the period of19thJuly2005 to 20thJuly2005.Under the steering of West Pacific subtropical high, "HaiTang"after landing in FU Jian for the two time moves in north-west direction.For detailedanalysis of the structure of storm rain bands caused by this Typhoon "Hai Tang",we use WRFmeso-scale model to simulate it high-frequnectly. The result indicates as follows.The coastalrainfall corresponds with the activity of the main and secondary rain bands.The main one causedby Vortex Rossby Waves is related well to 850hPa positive vorticity band and has seriousrainfall.Its low convergence level lies in somewhere of the maximum gradient of temperature andazimuthal winds,however the convergence level of the secondary one is higher than the formerone.Its maximum gradient of temperature andθ_e occurs above 700hPa level without thecoordinate of distinct gradient of azimuthal winds .It maily corresponds with ladder-shape frontalzone near the center of Typhoon.The merge of rain bands easily brings the increase of rainfall.We draw a conclusion from the evolution of MPV in cores of the main &secondary ones asfollows:the configuration of negative baroclinic term of MPV in lower levels & negativebarotropic term of MPV in higher levels is useful to the development of CSI,besides it ,it canindicate the rainfalls.During the period of the landing of Typhoon ,there exists the break of spiral rainbands.The divergence fields in the middle-low levels in the west and northwest of Typhooncenter result in the strengthening of cyclonic streamline in higher levels.The cyclonic streamline in high levels & the low-pressure in west merges into one,it brings mass convergence in this areaand caused spiral rain bands break off.When low pressure in higher levels forms obviouscyclonic shear,it breaks down the spiral rain band.The experiment of orographic height indicatesthat the orographic height not only affects the intensity of storm rainfall,storm smear etc,but alsoplays an important role in breaking off the spiral rain bands in land.Generally speaking,theorographic forcing accelerates the merge of the main rain band & the subordinate one.