本研究使用Wang and Zhang (2003)所提出之位渦及片段位渦反演法對模擬之颱風進行診斷，以瞭解颱風內部結構及非對稱平衡場的關係。反演出的平衡流場部分與高解析度WRF模式模擬聖帕颱風(2007)的流場相似，但在低層輻合和高層輻散會有相對較大的差異，低層差異來源主要可能是摩擦力從低層解析度較高的模式場內插到解析度較差的虛高座標，高層差異來源主要為較大的靜力穩定度和絕對渦度為正的假設。儘管有這些限制，在較強及快速之颱風發展階段都能顯示良好的反演結果。使用反演的平衡流場進一步計算準平衡旋轉流場及輻散流場的垂直運動，結果顯示，強烈颱風的流場頗為接近準平衡近似。將輻散流場分成潛熱釋放、摩擦力過程、乾動力過程的貢獻，發現潛熱會造成下層輻合與上層輻散及眼牆的上升運動，摩擦力作用造成低層的輻合與內區上升氣流類似Ekman pumping，而乾動力過程則與風切作用有關，風切作用的次環流可減少環境風切對颱風垂直結構的破壞作用。為了研究非對稱環流分布，使用片段位渦方法將內部颱風的位渦擾動分成眼牆正的位渦擾動、眼牆負的位渦擾動及眼的擾動。結果顯示去除眼的位渦擾動後，反演出的颱風眼牆環流的分布與環境駛流方向有關，在環境風方向的右（左）側大致上為負（正）的位渦擾動分布，反演出正（負）的非對稱壓力擾動及反氣旋（氣旋）擾動風場，而負的非對稱壓力擾動的分布則和颱風的垂直運動位置一致。

This study uses the PV inversion proposed by Wang and Zhang (2003) to diagnose the simulated typhoon for understanding how the intensity of the typhoon is related to the internal structure and the asymmetric balanced flow. Our inversion results for the simulated Typhoon Sepat (2007) with the high-resolution WRF model show that the balanced flow could well recover the characteristics of the original primitive flow (predicted by the model equations) except for the low-level convergence and high-level divergence. They could be attributed respectively to the use of reduced vertical resolution of the pseudo height at low levels and the assumptions of the required nonnegative absolute vorticity and larger static stability at high levels. In spite of these restrictions, the inversion results show that the original primitive flow is well inverted at both the stronger and faster developing stages of the typhoon. The results elucidate that quasi-balanced dynamics determines the typhoon flow to a large extent as compared to the primitive flow. With the quasi-balanced flow calculated from the PV inversion, the vertical motions can be attributed to different contributions from latent heating, friction, and the dry dynamic processes. The latent heating leads to low-level convergence, high-level divergence and major vertical motion in the eyewall. The friction effect causes the radial inflow in PBL and the updraft in the inner vortex to behave like the Ekman pumping. The dry dynamic processes are also influenced by the vertical shear. The shear-induced flow could reduce the destructive effects of the large-scale environmental shear. In order to study the asymmetric flow, the total PV perturbations are divided into positive PV and negative PV in the eyewall, and PV in the eye. It is shown that after removing the PV in the eye, the distribution of the inverted flow in the eyewall is related to the environmental steering flow. There are positive (negative) PV perturbations left (right) of the steering flow direction, with the inverted negative (positive) pressure perturbation and cyclonic (anti-cyclonic) flow. The negative asymmetric pressure perturbation collocates well with the upward motions. The superimposed inverted flows from the three piecewise PVs inside the eyewall are approximately in the same direction of the environmental steering flow.