Analysis On The Process Of Tropical Storm TOM's Transformation To Extratropical Cyclone

In the operational work of meteorological guidance for oceanic navigation, downgraded typhoons entering mid or high latitude, sometimes re-intensify unexpectedly, with intensity up to severe typhoon, and bring great threat to oceanic shipping. This sudden and unexpected occurrence is sometimes ignored by forecasters. By using MM5(V3-2), the transformation of TOM (a tropical storm in 1996 in Northwestern Pacific Ocean) from tropical storm to extratropical cyclone is simulated, also, the thermodynamic and dynamic structures are analyzed during Tom's evolution. The result shows that: 1) When tropical storm TOM 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) The main reason for severe convection in storm's northeastern part was the convergence and interactivity between cold air from northeastern part in low level and warm air from southwestern part, this brings about convective instability. 6) Through comparison of MM5's output and IR-TBB, MM5 may gave a satisfactory simulation about storm's track and precipitation, however, as most model, the intensity simulation was weaker than observation, especially the horizontal wind field in low level. Anyway, the model still showed the re-intensification process after TOM's downgrade from tropical storm to extratropical cyclone, demonstrating the 3 dimensional thermodynamic and dynamic structure characteristics during TOM's transformation.