台风“利奇马”(1909)冷空气和干空气侵入特征分析及数值模拟研究

Analysis and numerical simulation of cold air and dry air invasion characteristics of Typhoon“Lekima”(1909)

采用NCEP/NCAR再分析资料对2019年超强台风“利奇马”的干空气和冷空气侵入特征进行分析,并利用WRF模式进行数值模拟试验。结果表明:冷暖空气主要在台风西侧对峙,低层冷空气从台风西北侧随台风倒槽和西风槽旋转逐渐包围台风主体,随着槽后暖脊东移,中高层槽后冷空气逐渐被填塞,低层冷空气侵入更加明显。干空气在台风西侧聚集,中高层干空气从南侧侵入台风环流,破坏台风高层暖心结构,导致台风不对称性增强。数值模拟显示,冷暖空气对峙位置及强度与暴雨落区及强度有较好的对应关系。冷空气强度减弱后,侵入速度明显减慢,温度梯度减小且大值区偏西,低层辐合高层辐散的动力条件变差,造成降水减弱,雨带分布偏西。冷空气通过改变台风外围西风槽强度及温度梯度,影响急流强度,进而导致台风强度的变化。干空气在模拟前期由于水汽在旋转输入途中不断损耗,侵入速度减慢,对台风影响较小;在模拟后期,干空气侵入强度减弱后,对中高层结构破坏减弱,台风变性速度变慢。

Based on NCEP/NCAR reanalysis data,the invasion characteristics of dry air and cold air of super Typhoon“Lekima”in 2019 were analyzed and the WRF model was used for numerical simulation.Results show that the cold and warm air mainly confronts on the west side of the typhoon,the cold air in the lower layer gradually surrounds the typhoon from the northwest side with the rotation of the typhoon trough and the westerly trough,as the warm ridge behind the trough moves eastward,the cold air behind the middle and upper troughs is gradually filling,the cold air in the lower layer is more obvious.Dry air is distributed to the west of the typhoon,the middle and upper dry air intrudes typhoon circulation from the south and destroyed typhoon warm core structure,leading to enhanced typhoon asymmetry and typhoon gradually degeneration.The numerical experiment shows that the decrease of cold air intensity has obvious influence on precipitation area,typhoon intensity.The location and intensity of the confrontation between warm and cold air corresponded well with the precipitation area and intensity.The invasion of cold air is slower,the temperature gradient decreases and the large value region is to the west.The dynamic conditions of convergence at lower levels and divergence at higher levels become worse,which leads to a westerly distribution of rain bands.The cold air affects the westerly trough and jet intensity at first,causing the change of the thermal and dynamic structure outside the typhoon,and then gradually affects the internal structure of the typhoon,leading to the change of typhoon intensity.In the early stage of the simulation,the dry air is continuously lost due to the water vapor during the rotation.At the later stage of simulation,after the dry air invasion intensity weakened,the damage to middle and high level structures weakened and the speed of typhoon degeneration slowed down.