The Impact Of Vertical Wind Shear On Landfall Typhoons Activity

Which the latest 15-year(1990-2004) 111 landing typhoons in china, its intensity data, landing location data and NCEP/NCAR four-time/day reanalysis data for wind field and sea surface temperature data for past 153 years are used to study the impact of vertical shear in intensity change in the process of typhoons landing. We want to find out the effect of vertical shear in the sudden change of landing typhoons intensity. The article firstly divide the landing typhoons life into before-landing-phase, landing-phase and after-landing-phase. We mainly study the impact of vertical shear in intensity change in the landing-phase. After the phase of research, we find the impact of vertical shear is also existed. Compared with the open sea, the linear correlation between wind vertical shear and landing typhoons intensity is decreased, the extent of lag time is reduced together. The correlation between vertical shear and typhoons intensity of lag 6-12h is should not neglect. It is best when lag 6h as 0.215. To 18h, it is reduced to 0.163. When consider the predictable factor of typhoons intensity, we should give different proportions of vertical shear in different times. As the difference of underlying surface, the effect of landform, the change of vapor and so on, in a word, The Vertical wind shear is not so big when the landing typhoons intensity strengthen marked. It is average 9m/s. contrariwise, when the vertical shear is 9m/s, the landing typhoons intensity are also likely to decreased. The effect of wind shear is different as the other external factors are different. Then we divide the landing typhoons into landed in East China or South China based on the different landing locations. The intensity of landed in East China or South China typhoons are not deepening more, but landed in East China typhoons intensity will be weaken faster with the effect of vertical shear.This article analyzes the influence of wind vertical shear on the northwest pacific typhoon activity for the past 15 years. When the vertical shear increase and exceed the given value, the intensity and number of landing typhoons will be reduced. In the past 100 years, The SST is change fluctuant, but in the past 15years, it is in a warming process. After study the evolvement of vertical shear in the northwest pacific typhoon activity area, we discover that an enhancement in wind shear is associated with the global warming. We also find that wind shear change with the latitude and longitude and have a definite annual and interannual change.