热带气旋边界层的全息希尔伯特谱分析

Holo-Hilbert spectral analysis of tropical cyclone boundary layer

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10h的调制波和周期约为1~4h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.

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.