摘要
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.” With derived baroclinic diagnostic equations and a barotropical model,ten cases from 1980 to 1983 have been calculated for 24h typhoon motions.The results show that the baroclinic models are better than the baro- tropic ones.Therefore,the vertical wind shear is one of the important factors affecting typhoon movement.
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.” With derived baroclinic diagnostic equations and a barotropical model,ten cases from 1980 to 1983 have been calculated for 24h typhoon motions.The results show that the baroclinic models are better than the baro- tropic ones.Therefore,the vertical wind shear is one of the important factors affecting typhoon movement.
