INFLUENCE OF THE VERTICAL SHEAR OF ENVIRONMENTAL FLOWS ON TYPHOON MOTION

Typhoon is regarded as a convergent,modified Rankine vortex.Based on the vorticity equations written at two levels,higher and lower in the troposphere,typhoon motions are discussed in this study.The analytical expressions of vortex motion direction and speed have been derived for simple homogeneous basic flows at two levels.The expressions indicate that in the easterties,vertical wind shear enhances the steering of east flow,causing the vortex moving westward faster,otherwise,in the westerlies,it reduces the steering of the west flow,causing the vortex moving eastward slower.These results explain theoretically that "cyclones in the easterlies move to the right of,and faster than the basic flow;conversely,cyclones in the westerlies move to the left of,and slower than the basic flow."