The Diagnoses of Quasi‐Balanced Flows in Asymmetric Intense Hurricanes. Part II: Wave Structure

Abstract

AbstractIn this paper, the spatial structure and time series of mesoscale wave under the quasi‐balanced model in an asymmetrical intense hurricane are investigated by using the method of asymmetric wave decomposition and wavelet analysis. The results show that the wavenumber (WN)‐1 component of balanced flows predominated and manifest the typical feature of vortex Rossby waves (VRWs), while the spatial distribution of every component reflects a mixed feature of mesoscale waves. The wavelet analysis indicates that the strong wave signals of simulated and quasi‐balanced vertical velocity, which exceed the significance levels, contain high‐frequency waves of inertial‐gravity waves (IGWs), the low frequency waves of VRWs, and middle‐frequency waves of mixed vortex Rossby‐gravity waves (VRGWs). These mixed wave signals establish the path for exchanging the energy among different wavebands. The appearance and disappearance of mixed VRGWs signals are related to the violence development and weakening of TC. The strong wave signals of unbalanced vertical velocity are concentrated in the two regions of high and low frequency, reflecting that the formation and propagation of unbalanced vertical perturbation are the adjustment process relating to the high‐frequency gravity waves, which is influenced by the intensity change of TC. Environmental vertical wind shear plays an important role in the propagation of waves. When the shear is strong, the WN‐1 component in quasi‐balanced flows appears to be ‘standing waves’ both in tangential and radial directions. However, with the decreasing of vertical shear, the WN‐1 component propagates contrary to the basic flows at the phase speed of mixed waves.