热带风暴形成过程中的涡旋自组织及其复杂性:一个典型个例的红外云图分析

Vortex self-organization and its complexity during the development of a tropical storm: A case analysis based on the infrared satellite cloud images

应用高分辨率的红外卫星云图资料,对台风8807从热带低压发展成热带风暴的过程进行了分析,给出了热带风暴形成过程伴随着复杂涡旋自组织现象的观测证据。结果发现,涡旋自组织可在从数十到十万km2的各种尺度扰动云团之间发生,发生合并的云团除了理想数值试验中的两类前景之外,还存在第三类前景,即较大尺度的云团会发生分裂,部分与其他云团合并。合并形成的新云团可能发展也有可能减弱,这应取决于新云团所处的环境以及是否有其他云团补充并入。用二维Fourier分析可以清楚地看到8807发展成热带风暴的过程可分为两个阶段,一是多涡共存,不同方向、不同尺度系统能量转换频繁阶段,另一是单涡发展阶段,谱密度等值线形态稳定少变。分维计算结果表明,热带风暴形成过程中的相关云团较已有研究分析的云团略显规则,分维略小于已有结果。此外,临界温度取值不同,分维是有差异的,边界温度越低,分维越小。

Based on the high resolution infrared satellite data, this study focuses on the evolution of Typhoon Bill （8807） from tropical depression to tropical storm and shows the complicated vortices selforganizations during the development of the tropical storm. It is indicated that the self-organized cloud clusters could range from 10 to 100 000 km^2. Besides of the two scenarios from the ideal numerical experiments, there exits another scenario for the behavior of the self-organized cloud clusters. The larger cloud cluster could be divided into small clusters which partially merge with other cloud clusters. The new-merged cloud cluster may either strengthen or weaken, which depends on the embedding environment or the supplements of other cloud clusters. By using two-dimensional Fourier analysis, it is evident that the development of the tropical storm （8807） experiences two stages. The first is the multivortices coexistence, during which the energy transitions occur frequently between systems with various directions and scales. The other is the single vortex development stage, during which the pattern of the spectral density contours maintain stable. Fractal dimension calculations demonstrate that the cloud clusters related to the development of the tropical storm are more regular than those of previous studies, and the fractal dimension is smaller. Furthermore, fractal dimension varies considerably when the critical temperature is different. Specifically, the fractal dimension is smaller as the critical temperature is lower.