利用ARW—WRF模式,以垂直方向40个模式层(对低层加密)、水平方向最高1km的分辨率,对台风桑美(2006)进行数值模拟,模拟结果与实况基本一致。基于台风桑美(2006)1km分辨率的模拟结果,对台风低层(海面或地表以上1500m以下)风场结构进行了分析。结果表明,在台风登陆前,其最大风速半径附近存在水平风速在垂直方向有很强变化的风廓线,该类型风廓线的最大风速高度有明显变化,表现出类似急流的特征;而台风登陆后,其水平风速垂直变化明显减弱,即风廓线类型发生较大变化;另有一种水平风速在高层少变的风廓线类型在台风中是普遍存在的。还根据高层和低层两个切变因子,将台风登陆前的风廓线分为急流型、普通型和过渡型,并进一步分析各类风廓线在台风中出现的位置和急流高度。对急流型风廓线的形成原因也进行了初步探讨,结果表明,超/次梯度风在垂直方向上的变化是形成急流型风廓线的原因,而外围绝对角动量的输送在其中起关键作用。
In this study, the typhoon case of Saomai (2006) is well reproduced using the WRF-ARW system with a finest hori- zontal resolution of 1 km and vertical resolution of 40-model levels in which the lower levels are densified. Based on the 1 km simulated data of Typhoon Saomai (2006), the wind structure in the lower levels (below 1500 m height over sea level or ter- rain) over the typhoon are analyzed. The strong vertical shear of horizontal wind speed is found near the radius of maximum wind (RMW) during the typhoon staying over sea. Two shear factors for the high levels and low levels, respectively, are de- fined. And then vertical profiles of horizontal wind speed are categorized into four types according to the two shear factors, two of which are stronger in shear and belong to jet type profiles. Further, their locations in the typhoon and the jet heights for the four type vertical profiles of horizontal wind are analyzed. And the possible causes of generating the two jet type profiles are al- so analyzed and discussed. The results show the changes of supergradient/subgradient wind in the vertical direction should be responsible for the jet type profiles and the advection of angular momentum plays an important role in it. However, no jet type profile is found after the typhoon landed.