有限区域流函数和速度势的计算及其在台风中应用

Computation of stream function and velocity potential in a limited area and its application to typhoon

在Endlich提出求解旋转风和辐散风基础上,本文给出了直接利用风场迭代计算流函数和速度势的方法,该方法不但能求解流函数和速度势,还可将原始风场直接分解为旋转风和辐散风。此方法在有限区域中,能大大降低边界条件对计算结果的影响,不仅能计算准确的涡度和散度,还能很好的重建原始风场。采用此方法,对"0808"号台风"凤凰"进行了诊断分析,得到了台风不同时期的流函数和速度势、旋转风和辐散风。结果发现在台风的不同时期,流函数与高度场相似,可用其低值中心来分析台风移动路径和强度的变化,速度势存在高值区,其中心与高度场低值中心不吻合;旋转风的涡旋中心也可用来反映台风中心,台风南侧辐散风较大,故可用来反映南方水汽供应对台风发展、成熟、衰退的影响。

This paper gives an iterative method of calculating directly stream function and velocity potential from wind field based on the Endlich＇s idea of figuring out divergent wind and rotational wind.This method not only obtains stream function and velocity potential,but also partitions the wind into divergent wind and rotational wind.The results of calculation showed that in a limited area the iterative method can eliminate boundary effects on results,and can restructure original wind well.This method is used to diagnose the typhoon ＂Fung-wong＂ and calculate the stream function,velocity potential,divergent wind and rotational wind at different periods of typhoon with the data of NCEP/NCAR reanalysis.The results suggest that at different periods of typhoon,stream function is similar to the height field,and their low value＇s centers are basically consistent each other,but the high value＇s center of velocity potential is not.So the low center and the minimum of the stream function can be used to diagnose center position,motion track and intensity of typhoon.Meanwhile,the vortex center of rotational wind can be used to reflect the center of typhoon too,and the divergent wind is stronger in the south of typhoon that reflects the effects of vapour supply on typhoon of the different periods.