ISSN 1006-9895

CN 11-1768/O4

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

    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.

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History
  • Received:March 09,2015
  • Revised:
  • Adopted:
  • Online: September 24,2016
  • Published: