Model output data from WRF (v3.4) are used in this study to analyze the influence of the vertical wind shear (VWS) on typhoon structure and intensity. A wave vertically distribution of VWS is revealed. The wave varies with different stage of typhoon development, and exhibits bimodel distribution in the mature stage. Based on the general mechanism of VWS's influence on typhoon's intensity and distribution of convection, we found the VWS in the middle troposphere is the major part of the total VWS. The change of the typhoon intensity occurs about 6 hours after the abrupt change of VWS's wave. The secondary circulation induced by bimodel VWS creates an asymmetric deep convection structure and a non-homogeneous vertical distribution of convection in eye wall. With the increased intensity of cyclonic circulation, the distribution of strong convection tends to be symmetric gradually. According to the mechanism that VWS-induced uneven distribution of vorticity can initialize mesoscale convective-rolls associated with convective instability, we also found the vorticity in the lower-to-middle troposphere is favorable for development of convective instability. The maximum vertical velocity is generally at the same altitude with the inflection of the vertical wind profile, which is consistent with the results from theoretical models. Therefore, the bimodel VWS not only has influence on the change of the mesoscale structure of strong convection in typhoons, but also is crucial to the maintenance of a strong mature typhoon. Furthermore, the wave distribution of VWS might be the trigger of instability accounting for the convective-rolls in typhoon.
