ULTRA-HIGH RESOLUTION SIMULATION OF LOW-LEVEL UPDRAFT EXTREMES IN THE TROPICAL CYCLONE EYEWALL
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摘要: 观测发现热带气旋(TC)眼墙附近低层(3 km以下)存在着强烈的上升运动，严重威胁低空观测飞机的安全，由于对实际TC观测的样本非常有限，目前对极端上升运动(大于10 m/s)的了解不多。通过三个水平分辨率自次千米(333 m)至次百米(37 m)大涡数值试验模拟眼墙附近低层上升运动的分布特征。结果表明，TC眼墙附近的最强上升运动主要分布在眼墙处最大风速半径(RMW)内侧，并且主要出现在台风眼墙强对流的一侧。对比不同试验发现，在大涡试验中，随着模式水平分辨率的提高，模式可以模拟出更强的上升运动，且极端上升运动最大频数的分布高度随着水平分辨率的提高而降低。研究表明，与现有观测结果比较，当大涡试验水平分辨率到达111 m时，可以模拟出与实际观测比较相似的极端上升运动空间分布和强度。Abstract: Observation shows very strong upward motion in the low-level (below 3 km) eyewall of the tropical cyclone (TC), which seriously threatens the safety of low-altitude observation aircraft. Since the TC observation is limited in the sample size, the extreme updraft (larger than 10 m/s) is not fully understood. In this study, four numerical simulations with resolutions from the sub-kilometer (1/3 km) to sub-hundred meter (1/27 km) are conducted to investigate the low-level updraft extreme near the eyewall. Results show that the strongest updrafts near the eyewall are located in the inner side of the radius of the maximum wind (RMW). Increasing the horizontal resolution in a large eddy experiment, the magnitude (frequency) of the extreme updraft increases. In addition, when the horizontal resolution of the large eddy experiment reaches 111 meter, the spatial distribution and magnititude of the extreme updraft are comparable to the observation.
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图 3 积分30 h 3 km高度上台风眼墙区域模拟雷达回波(dBz)的填色图
a. LES333；b. LES111；c. LES37。蓝色圆环以3 km上台风中心为圆心，最大风速为半径。箭头为积分24~36 h 200 hPa和850 hPa之间大尺度环境场平均垂直风切变，其强度分别为5.8 m/s、5.8 m/s和5.9 m/s。
图 4 积分25~36 h台风方位角平均的径向风和切向风的纵截面
a. LES333；b. LES111；c. LES37。填色图为切向风(m/s)间隔为2.5 m/s，等值线为径向风(m/s)，实线为径向入流，虚线为径向出流，加粗实线为0 m/s。
图 5 积分30 h东北象限500 m高度上垂直运动的水平分布
a. LES333；b. LES111；c. LES37。其中横纵坐标为与TC中心的距离，同心圆间隔为5 km。
图 6 积分30 h东北象限500 m高度上垂直运动的水平分布
a. LES111降分辨率结果；b. LES37降分辨率结果。其中横纵坐标为与TC中心的距离，同心圆间隔为5 km。
图 8 积分24~36 h W10、W15和W20与台风中心相对位置
横纵坐标为W10、W15和W20与台风中心相对位置与其对应最大风速半径(RMW)的比值。a. LES333；b. LES111；c. LES37。红色圆环为最大风速半径所在位置，内外两侧的黑色虚线圆环为0.5倍RMW和1.5倍RMW的位置，箭头为积分24~36 h 200 hPa和850 hPa之间大尺度环境场平均垂直风切变，其强度为5.9 m/s。
表 1 数值试验网格设置和边界层方法
试验名称 PBL 嵌套格点(区域) 水平分辨率 LES333 LES 721×721(240km) 1/3km LES111 LES 1351×1351(150km) 1/9km LES37 LES 2431×2431(90km) 1/27km 
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表 2 三个试验3 km以下眼墙区域不同强度垂直运动的占总格点的比例
试验名称 W5/% W10/% W15/% W20/% LES333 1.8 7.5×10-2 5.3×10-3 2.8×10-4 LES111 2.1 0.1 8.9×10-3 9.1×10-4 LES37 1.5 5.9×10-2 3.6×10-3 4.7×10-4
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表 3 三个试验3 km以下强对流区域不同强度垂直运动的占强对流区域格点的比例
试验名称 W5/% W10/% W15/% W20/% LES333 2.40 0.11 7.40×10-3 4.00×10-4 LES111 3.10 0.16 1.50×10-2 1.40×10-4 LES37 2.30 9.40×10-2 6.70×10-3 7.70×10-4
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