南京大学学报(自然科学版)

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热带气旋边界层的全息希尔伯特谱分析

赵睿峰,谈哲敏(),雷荔傈   

  1. 南京大学大气科学学院，南京，210023
  • 收稿日期:2020-05-06 出版日期:2020-09-30 发布日期:2020-09-29
  • 通讯作者: 谈哲敏 E-mail:zmtan@nju.edu.cn
  • 基金资助:
    国家重点研究发展计划(2017YFC1501601)

Holo⁃Hilbert spectral analysis of tropical cyclone boundary layer

Ruifeng Zhao,Zhemin Tan(),Lili Lei   

  1. School of Atmospheric Sciences, Nanjing University, Nanjing, 210023, China
  • Received:2020-05-06 Online:2020-09-30 Published:2020-09-29
  • Contact: Zhemin Tan E-mail:zmtan@nju.edu.cn

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摘要：

在一个理想热带气旋(Tropical Cyclone,TC)的大涡模拟试验基础上，利用全息希尔伯特谱分析方法计算了热带气旋边界层(TC Boundary Layer,TCBL)中眼墙(内核区)和外核区不同高度的切向和径向风速、垂直上升运动以及假相当位温的能谱，讨论了TCBL中湍流、小尺度涡旋与热带气旋较大尺度过程之间可能存在的调制关系.结果表明，热带气旋强度变化、涡旋罗斯贝波和涡丝化等较大尺度过程是调制TCBL中小尺度扰动的重要因子.此外，在TC不同位置和不同高度的切向风速能谱都具有较强的一致性，涡旋罗斯贝波的传播对径向风速的影响要大于对切向风速的影响.对于垂直上升运动的能谱，TC强度变化的调制信号相对贡献减小，而低频调制波的作用更加明显.假相当位温能谱存在周期大约为10 h的调制波和周期约为1~4 h的载波信号，这表示涡旋罗斯贝波的径向能量外传可能是导致TC边界层恢复的原因之一.

关键词: 热带气旋, 边界层, 全息希尔伯特谱, 大涡模拟

Abstract:

An idealized large?eddy simulation of tropical cyclone (TC) is conducted. Holo?Hilbert Spectral Analysis (HHSA) is used to calculate the spectra of tangential wind speed,radius wind speed,vertical updraft motion and pseudo?equivalent potential temperature at different heights at the eyewall (inner?core) and the outer?core region in TC boundary layer (TCBL). The modulated relationship between small scale processes and larger scale processes in TCBL is discussed. The results of HHSA reveal that larger scale processes including the TC intensity change,the propagation of vortex Rossby waves,and vortex filamentation process play important roles in modulating turbulence and small scale vortices in TCBL. In addition,HH spectra of tangential wind speed are consistent at different locations and heights. This is not the case for HH spectra of radial wind speed,which exhibit a stronger signal of modulation by the propagation of vortex Rossby waves. In the HH spectra of the vertical updraft motion,the relative contribution of modulation by the TC intensity change decreases,while the effect of the low?frequency modulation wave is stronger. The spectra of pseudo?equivalent potential temperature have a signal where the modulation period is about ten hours and the carrier period is about one to four hours,which indicates that the energy propagation of vortex Rossby waves in radial direction may be one of the reasons for the recovery of TCBL.

Key words: tropical cyclone, boundary layer, Holo?Hilbert spectrum, large?eddy simulation

中图分类号: 

  • P447

图1

HHSA算法流程图The blue arrows represents the frequency or amplitude of IMFs."

图2

热带气旋的海平面最低气压(实线)和10 m最大切向平均风速(点线)随时间的演变(a) S1 experiment,(b) LES experiment and the radius of maximum mean tangential wind in LES experiment D02 (dashed line)"

图3

LES试验中，热带气旋在距离中心120 km区域内每两个小时的最大雷达反射率(单位：dBZ)"

图4

(a) LES试验D02示意图；(b) D02网格0时刻热带气旋中心60 km区域的10 m最大风速(单位：m?s-1)"

图5

切向风在不同半径位置和高度的时间演变序列：(a) RMW处，(b) 3*RMW处；不同半径位置、高度的HH谱：(c) RMW处，200 m高度，(d) 3*RMW处，200 m高度，(e) RMW处，500 m高度，(f) 3*RMW处，500 m高度，(g) RMW处，1000 m高度，(h) 3*RMW处，1000 m高度；不同半径位置、高度的傅立叶谱 ：(i) RMW处，(j) 3*RMW处The rectangles in subgraph (c) represents different physical processes: the TC intensity change (blue),vortex filamentation process (pink) and turbulence and small scale convective motions (green)."

图6

24 h内的海平面最低气压的EMD分解结果The orange line is temporal evolution of minimum sea level pressure,the thick light yellow line is the trend,and the blue lines C1~C8 are the eight IMFs (components) obtained through EMD."

图7

不同高度的平均涡丝化时间径向廓线The dotted line is the average of 10~12 h and the solid line is the average of 20~22 h. Different colors represents different heights,blue: 200 m,orange: 500 m,light yellow: 1000 m. RMW is about 16.2 km and 3*RMW is about 48.6 km."

图8

径向风速随时间变化及对应的HH谱和傅立叶谱，其他同图5The rectangles in subgraph (g) represents different physical processes: the TC intensity change (blue),the propagation of vortex Rossby waves (green) and the energy propagation of vortex Rossby waves in radial direction (pink)."

图9

1000 m高度1~3波数扰动相对涡度振幅的时间–半径Hovm?ller图"

图10

垂直上升运动随时间变化及对应的HH谱和傅立叶谱，其他同图5The rectangles in subgraph (e) represents different physical processes: the TC intensity change (blue),the propagation of vortex Rossby waves (green) and vortex filamentation process (pink)."

图11

假相当位温随时间变化及对应的HH谱和傅立叶谱，其他同图5The rectangles in HH spectrum (g) represents different physical processes: the TC intensity change (blue),the recovery of TC boundary layer (light blue),the propagation of vortex Rossby waves (green) and vortex filamentation process (pink)."

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