Numerical Simulate Research On The Process Of Tropical Storm KOPPU's Transformation To Extratropical Cyclone

First, this paper summarize climate feature of extratropical transition by112 extratropical cyclone from tropical strom transformation in 3000 extratropical cyclone about 20 years and Klein research 30 transformation fron 1994-1998,also this paper give a simple model on transformation :transformation beagin ,transformation end and reintensification.Satellite imagery is a good tool at present, this paper analysis satellite imagery and summrize feature:use a few simple sentences:a)a marked decrease of deep cloudiness and rainband outside the inner core in the western quadrant,the result is an asymmetric appearance of clouds and deep convection compared to the moresymmetric structure during the mature stage of tropical cyclone. And dry slots also appear between rainbands in the southern quadrant.b)cirrus "shield"that features a sharp edge,which implies confluence between this outflow from the transforming strom and the polar jet c)the erosion of inner-core deep convection to produce dry:gaps"in what was once the eyewall.extratropical transition and decayer is similar in first step from satellite imagery.tropical strom KETSANA far away midlatitude baroclinic zone, without role with max polar.By using WRF model, the transformation of KOPPU (a tropical storm in 2003 in Northwestern Pacific Ocean) from tropical storm to extratropical cyclone and untransformation KETSANA that will be classifed as "decayer" is simulated, also, the thermodynamic and dynamic structures are analyzed during koppu's evolution. The result shows by contrast of KOPPU and KETSANA that: Extratropical transition is defined in term of two stages:transformation,in which the tropical cyclone evolves into a baroclinic and reintensification.Case(ketsana)that begin transformation but do not become embedded in the baroclinic zone fail to complrte transformation and simply dissipate over lower sea surface temperatures.1)at transformation stage,there are two features in 500mb analysis a)KOPPU 's surface center is located beneath concentric,closed 500mb contours and is equatorward of 5820-m contour associated with a short-wave trough to the northwest of strom b)the closed contours associated with KOPPU 24h earlier have combined with approaching 500mb trough so that KOPPU appear to be in an open wave.furthermore,streamlines associated with this short wave trough have wrapped around the circulation of KOPPU,which indicated that KOPPU has become embedded in 500mb westerlies. When tropical storm KOPPU entered mid-high latitude of baroclinic zone, cold air in 850hPa began to erode TOM's warm core, without changing its warm feature in low level. Only when TOM coupled with 500hPa westerly trough and interacted each other, the cold air after the trough destructed completely the warm core, changing the previous warm feather from up to low level, and made it become a extratropical cyclone. 2) Vertical wind shear in the storm's northern part was favorable for the transformation from barotropical to baroclinic structure. 3) Extratropical cyclone's warm frontal genesis was more significant than that of cold front. 4) After storm's entering westerly trough, the subtropical cyclone's reintensification was related to the high potential vortex's downward transmission from stratosphere. 5) dry, cold air is induced reaction of transformation.6)vertical wind shearIS a important role 7) the interaction stage of tropical cyclone with a midlatitude baroclinic zone was an essentialcomponent.