藤田公式改进及其在台风预报中的应用

Improvement of Fujita Formula and Its Application in Typhoon Forecasting

在考虑环境气压的影响下,引进环境半径参量对藤田公式改进并将其应用到9711号台风研究预报中。结果表明:①改进的藤田公式能够基本解决藤田公式计算的外围气压和气压梯度偏小这一问题,合理地给出整个台风域内气压和气压梯度力的分布。②改进的藤田公式由于引入了环境半径的影响,使得计算的风向内偏角减小而风速增大;特别是它能使台风外围的风速增大而风向内偏角减小,进而改变台风的内部结构。③不论是风向内偏角还是风速,在距台风中心一定距离范围内,摩擦力对风向内偏角和风速的影响都很小,但当超过这个距离时,风向内偏角和风速均随摩擦系数变化而急剧变化;且在同距离同摩擦系数条件下,应用改进的藤田公式计算的风向内偏角变小而风速增大。④讨论环境的影响(即引入有界环境半径参量),能够使计算的台风外围气压和气压梯度增大,风向内偏角减小,风速增大。当环境半径参量趋于无穷大时,改进后量的状态无限趋近于没有改进时量的分布。

The environmental radius into the Fujita formula by consideration of environmental pressure is introduced and applied in improving typhoon 9711 forecasting.The results show that：（1） the improved Fujita formula can basically solve the problem that the computed peripheral pressure and pressure gradient are too small,and also gives a reasonable distribution of pressure and pressure gradient force within the typhoon areas;（2） the improved Fujita equation,due to the impact of the environmental radius,makes the computed wind inner deflection angle smaller and wind speed greater,and in particular,changes the internal structure of the typhoon;（3） in either the wind direction or wind speed,in the range of a certain distance from the center of the typhoon,the friction force has a very small effect,but beyond this distance,both wind inner deflection angle and wind speed have a sharp increase with the gradient of friction coefficient;and at the same distance with the same friction coefficient,the improved Fujita formula gives smaller wind inner deflection angle and greater wind speed;（4） by considering the environmental influence（i.e.,the introduction of a bounded environment radius parameter）,the calculated typhoon periphery pressure and pressure gradient are greater,the wind inner deflection angle smaller,and the wind speed greater.When the environment radius tends to be infinite,the improved status of Fujita formula tends to be un-improved.