登陆台风近地层湍流特征观测分析

ANALYSIS ON BOUNDARY LAYER TURBULENT FEATURES OF LANDFALLING TYPHOON

  • 摘要: 在对多个登陆台风实地观测的基础上,选取出较有代表性的实验观测个例:“黄蜂”、“杜鹃”和“黑格比”3个登陆台风,分析探讨在登陆台风的中心、靠近中心位置的强烈影响区域和台风外围环流影响地区近地层湍流特征,以期对登陆台风的边界层湍流过程有所认识。观测资料分析显示,在登陆台风的中心及其强烈影响的区域:(1)风速和湍流强度均有强烈的变化;(2)水平湍流积分尺度明显增大,越靠近中心位置,增大越明显,而垂直方向没有明显变化;(3)在湍流谱的低频和高频区,湍能均可增大1~2个量级,其中垂直方向湍能增大的幅度略小于水平方向;(4)湍谱在惯性子区u,v,w3个方向的分布均不满足-5/3次方律,存在较大偏移,而在台风外围环流影响区和无台风影响时,则无上述的4个特征。

     

    Abstract: Typhoons are one of severe weather systems inducing severe catastrophe in the coastal regions in China.Investigation on characteristics of near-surface turbulence of landfalling typhoons is vitally important for better understanding of inner structure and movement of typhoons, characters of disasters so arisen, as well as sustaining period of typhoons. Furthermore, near-surface turbulence activities of landfalling typhoons have enormous impact on buildings, safety of lives and properties in the typhoon affected regions. Based on a number of observations on landfalling typhoons, three representative cases of “Vonfong”, “Dujuan” and “Hagupit” were chosen in the article to analyze near surface turbulence characteristics in the typhoon center, severely affected areas near typhoon center and their peripheral areas of typhoon. It is expected through this study to improve our understanding of near -surface turbulence characteristics of landfalling typhoons. In-situ observations were carried out using CSAT3d type of three dimensional supersonic anemometer manufactured by Campbell Science in USA, with data sampling frequency of 10Hz. The supersonic anemometer is capable of automatically providing data quality codes to eliminate invalid data. Therefore, interference on data accuracy by rainfall can be avoided. In this study, multiple samples were chosen to analyze for each typhoon processes with each sampling length of 30 minutes, and over 98% valid data for each sample. Each sample is processed to satisfy the requirement of stable stochastic process by applying linear interpolation technique to interpolate at data void points, and second order polynomials fitting to remove trend in the time series.Through computational analysis on the observational data of typhoons “Vonfong”, “Dujuan” and “Hagupit”, Preliminary results may be obtained as following:(1) In the center and its adjacent areas of a landfalling typhoon, horizontal wind speeds and directions change dramatically, with significant downdraft in the vertical.(2) In the center or its adjacent areas of a landfalling typhoon, turbulence intensities increase enormously, and may increase over two times in the principal wind direction. (3) In the center area of a landfalling typhoon, the turbulence integral scale can be expanded significantly in the principal wind direction, closer to the center, more significant the scale expansion. In the center of a landfalling typhoon, the turbulence integral scale l may be expanded by one order in horizonta, while no evident change of turbulence integral scale can be manifested in vertical.(4) In the centre or its adjacent areas of a landfalling typhoon, the turbulence spectral in the inertial range does not satisfy the assumption of isotropy. Neither do the slope rates of turbulence spectra in u, v and w directions satisfy the -5/3 law. The deviation amplitude generally exhibits in vertical>side>principal wind direction, i.e. the slope rates in the inertial range were 0.6—0.8 in vertical wind direction, 0.9—1.0 in side wind direction and 1.0—1.4 in principal wind direction. However, in the peripheral circulation of typhoon, the assumption of isotropy is basically satisfied, with the slope rates in accordance with the rule of “-5/3” power.(5) In the centre or its adjacent areas of a landfalling typhoon, turbulent energy can increase by 1 to 2 orders in both low and high frequency domains. The amplitude of increase is less in vertical than in horizontal. However, in the periphery of typhoon circulation, no evident change of turbulent energy was observed.

     

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