登陆台风“凡亚比”(1011)合力散度特征诊断研究——垂直分布特征

本文利用2010年1011号台风“凡亚比”登陆过程高分辨率数值模拟资料，诊断分析了“凡亚比”台风环流合力散度的垂直分布及其演变特征。结果指出，合力散度的显著区一直与台风系统相伴随，可以有效地示踪热带气旋（Tropical Cyclone，简称TC）的移动，并能较好地识别TC强度、结构的发展演变。台风中心偏东一侧流入层的合力散度异常信号首先出现并发展，反映出环流的非对称特征。随着台风趋于成熟，合力散度逐渐增强，高度扩展，对称性也逐渐增加；台风中心上空为合力辐合，外围为合力辐散，垂直方向上合力辐合与辐散相间的结构对应上升运动极值区及强降水，即对应台风眼墙位置。合力散度面积指数和强度指数的分析指出，垂直方向上辐合与辐散面积指数负相关；各层的合力辐合强度指数普遍大于辐散强度指数，垂直方向上两强度指数呈显著的正相关关系；结合面积指数与强度指数，可知垂直方向上合力辐合与辐散此消彼长。运用合力散度方程对该垂直分布特征的成因展开分析，发现风速u分量平流随经度变化项和风速v分量平流随纬度的变化项是TC眼区合力辐合部分的主要贡献项，垂直运动项决定了TC眼墙的合力辐合与辐散相间的垂直分布特征。

Diagnostic Analysis of Characteristics of Vertical Distribution of Total Force Divergence for the Landfalling Typhoon Fanapi (1011)

Diagnostic analysis is performed in this study to investigate the vertical distribution characteristics and evolution features of the total force divergence/convergence (hereafter TFDC) for the landfalling typhoon Fanapi (1011) based on high-resolution simulations and calculation of the TFDC equation. It is found that typhoon Fanapi is always accompanied by significant TFDC zone, which thereby is capable of tracking tropical cyclone (TC) movement and identifying the evolution of TC intensity and structure. The distinct TFDC signal first occurs within the inflow layer to the east of the TC center and grows rapidly, demonstrating the asymmetrical feature of TC circulation during its rapid intensification stage. As Fanapi further intensifies, the total force divergence and convergence increase and stretch vertically, and become more symmetric. The total force convergence zone is located above the TC center in the upper level while the total force divergence zone is found in the periphery of the TC. Their interface corresponds to the area of strong ascending motion and heavy precipitation, which actually indicates the position of the TC eyewall. Analyses of the TFDC area index and intensity index have revealed that in the vertical direction, the convergence area index is negatively correlated with the divergence area index, while the two intensity indices are significantly positively correlated. Generally, the convergence intensity index is larger than the divergence intensity index in each individual layer. Looking at the combination of area index and intensity index, it is clear that in the vertical, the total force is subjected to low-level convergence and upper level divergence, and vice versa. The formation of characteristic distribution of the TFDC is diagnosed Based on the TFDC equation. Results indicate that the partial derivatives of advection of wind component U with respect to longitude and that of wind component V with respect to latitude are two major terms contributing to the total force convergence inside the TC eyewall, and the vertical motion dominates the distribution of the total force convergence and divergence over the area of TC eyewall and its vicinity.