南京大学学报(自然科学版) ›› 2024, Vol. 60 ›› Issue (2): 230–243.doi: 10.13232/j.cnki.jnju.2024.02.005

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热带气旋发展增强过程中龙卷尺度涡旋活动特征

周玥滢, 方娟()   

  1. 中尺度灾害性天气教育部重点实验室，南京大学大气科学学院，南京，210023
  • 收稿日期:2024-02-24 出版日期:2024-03-30 发布日期:2024-03-29
  • 通讯作者: 方娟 E-mail:fangjuan@nju.edu.cn
  • 基金资助:
    国家自然科学基金(42175004)

Characteristics of tornado⁃scale vortices in an intensifying tropical cyclone

Yueying Zhou, Juan Fang()   

  1. Key Laboratory of Mesoscale Severe Weather，Ministry of Education，and School of Atmospheric Sciences，Nanjing University，Nanjing，210023，China
  • Received:2024-02-24 Online:2024-03-30 Published:2024-03-29
  • Contact: Juan Fang E-mail:fangjuan@nju.edu.cn

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摘要：

观测发现热带气旋（TC）边界层中存在龙卷尺度涡旋（TSV），其引起的相关阵风对近地面具有强烈影响.利用WRF?ARW模型，通过对飓风Earl （2010）进行高分辨率的数值试验模拟，分析了TC边界层龙卷尺度涡旋的时空分布特征以及发生发展的可能原因.Earl发展增强过程中，TSV数量随着Earl强度的增强而增加，尤其在最强期间表现最为活跃，一方面TC的增强提供了更强的背景场使得TSV更易生成，另一方面更强的背景场使得长生命期的TSV增加，每一时刻同时存在的TSV也就更多.TSV生成区域随Earl的发展从垂直风切左侧逐渐集中至逆风切左侧，且始终位于RMW内侧近地层次级环流上升支和最大垂直涡度位置附近，这里通常满足垂直切变和水平切变不稳定的必要条件，TSV涡度收支分析的结果表明，对TSV生成发展起主要贡献的是与水平风水平切变相关的拉伸项以及与垂直切变相关的扭转项，这意味着TSV的生成与发展可能与垂直切变不稳定和水平切变不稳定有关.

关键词: 热带气旋, 龙卷尺度涡旋, 垂直切变, 水平切变

Abstract:

Observations have revealed the presence of tornado?scale vortices (TSVs) within the boundary layer of tropical cyclones (TCs)，which significantly impact near?surface gustiness. Based on Weather Research and Forecasting Model ? Advanced Research WRF (WRF?ARW)，a high?resolution numerical experiment in simulating Hurricane Earl (2010) is conducted to analyze the activity characteristics of TSVs in boundary?layer. During the strengthening process of Earl，the number of TSVs increases with the intensification of Earl，especially during its peak. On one hand，the strengthening of the tropical cyclone (TC) provides a stronger background field，making it easier for TSVs to form. On the other hand，the stronger background field leads to an extended lifespan for TSVs，resulting in a higher number of concurrent TSVs at any given moment. The area that TSV generating gradually shifts from the left side of the vertical wind shear to the up?shear left as Earl develops，near the secondary circulation updraft and the maximum vertical vorticity，where often meets the necessary conditions of unstable vertical and horizontal wind shear. The results of TSV vorticity budget analysis further indicate that the stretching term associated with horizontal wind shear and the tilting term associated with vertical wind shear are important factors in the generation and development of TSVs，which implies that the generation and development of TSV may be related to vertical shear instability and horizontal shear instability.

Key words: tropical cyclones, tornado?scale vortex, vertical shear, horizontal shear

中图分类号: 

  • AP444

图1

数值试验六重网格嵌套示意图"

图2

模拟的(a)路径、(b)最小海平面气压（SLP，单位：hPa）和(C) 10 m最大风速（单位：m·s-1）The gray line represents the optimal path and the red line represents data from numerical simulations.(c) 10 m maximum wind speed (unit: m·s-1)"

图3

Earl发展增强过程中TSV数目随时间的变化The red and blue lines indicate the number of TSVs obtained using identification conditions with vertical velocities greater than 15 and 20 m·s-1，respectively."

图4

30日17-19时（实心柱）和31日05-07时（空心柱）TSV中不同生命期长度的占比情况"

图5

30日00时至31日09时200 m高度上风速（单位：m·s-1）的填色图，黑色圆环表示200 m高度上最大风速半径，矢量箭头为200~850 hPa环境场垂直风切变，黑色圆点代表TSV"

图6

30日18时至31日09时（a，d，g，j）方位角平均切向风（阴影，单位：m·s-1）和径向风（等值线，间隔1.0 m·s-1）；（b，e，h，k）方位角平均雷达回波（阴影，单位：dBZ）和垂直速度（等值线，间隔0.5 m·s-1）；（c，f，i，l）方位角平均相对涡度（阴影，单位：s-1）和相当位温（等值线，间隔1 K）；紫色空心圆代表识别出的TSV，灰色实线代表最大风速半径"

图7

30日00时到31日10时1 km高度以下平均的Ri，黑色圆环表示200 m高度上最大风速半径"

图8

30日18时和31日06时1 km高度以下平均的（a， c）浮力振荡频率N2（单位：s-2）和（b， d）水平风垂直切变S2（单位：s-2），黑色圆环表示200 m高度上最大风速半径"

图9

30日00时至31日10时200 m高度上轴对称叠加1波的垂直相对涡度（单位：s-1）Black circles indicate the radius of maximum wind speed at 200 m height."

图10

30日00时至31日10时200 m高度上轴对称叠加1波的Fjortoft判据The black circle indicates the radius of the maximum wind speed at 200 m height，and the red circle indicates the radius ofthe axisymmetric vertical relative vorticity maxima at 200 m height."

图11

形成于30日17:48前后（a） 100 m和（c） 200 m高度上；31日06:01前后（b） 100 m和（d） 200 m高度上的一个TSV的涡度变化以及涡度收支各项随时间的变化The red solid line is the regionally averaged vorticity magnitude (unit: s-1)，the black solid line is the vorticity tendency (unit: s-2)，the red dashed line is the horizontal advection term (unit: s-2)，the blue dashed line is the vertical transport term (unit: s-2)，the purple dashed line is the torsion term (unit: s-2)，and the green dashed line is the stretching term (unit: s-2)."

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