Impact of Asymmetric Dynamical Processes on the Structure and Intensity Change of Two-Dimensional Hurricane-Like Annular Vortices

Abstract

In this study, a simple two-dimensional (2D) unforced barotropic model is used to study the asymmetric dynamics of the hurricane inner-core region and to assess their impact on the structure and intensity change. Two sets of experiments are conducted, starting with stable and unstable annular vortices, to mimic intense mature hurricane-like vortices. The theory of empirical normal modes (ENM) and the Eliassen-Palm flux theorem are then applied to extract the dominant wave modes from the dataset and diagnose their kinematics, structure, and impact on the primary vortex.From the first experiment, it is found that the evolution and the lifetime of an elliptical eyewall, described by a stable annular vortex perturbed by an external wavenumber-2 impulse, may be controlled by the inviscid damping of sheared vortex Rossby waves (VRWs) or the decay of an excited quasimode. The critical radius and structure of the quasimode obtained by the ENM analysis are shown to be consistent with the predictions of a linear eigenmode analysis of small perturbations. From the second experiment, it is found that the outward-propagating VRWs that arise due to barotropic instability and the inward mixing of high vorticity in the unstable annular vortex affect the primary circulation and create a secondary ring of enhanced vorticity that contains a secondary wind maximum. Sensitivity tests performed on the spatial extent of the initial external impulse verifies the robustness of the results. That the secondary eyewall occurs close to the critical radius of some of the dominant modes emphasizes the important role played by the VRWs.

An Analysis of Dynamic Instability on TC-Like Vortex Using the Regularization-Based Eigenmode Linear Superposition Method

“…This indicates that the WN-2 disturbance is completely controlled by the most unstable mode, and the perturbation change caused by the mode development also is large enough to affect the structure and intensity change in the vortex system. The result is well consistent with the work of Menelaou et al [22] based on the theory of empirical normal modes. …”

“…The ENM technique begins with the decomposition of a disturbance into a set of basis functions [21]. Menelaou et al [22] extracted the dominant wave modes from the dataset and diagnosed their kinematics, structure and impact on the primary vortex by the theory of ENM and the Eliassen-Palm flux theorem. Note that, although the ENMs are the eigenvectors of the eigenproblem, the corresponding eigenvalues do not represent eigenfrequencies and each ENM is not a single wave.…”

Hurricane Eyewall Evolution in a Forced Shallow-Water Model

“…The instability of the eyewall, its breakdown, and subsequent potential vorticity mixing between the eyewall and eye has been examined extensively in idealized numerical modeling frameworks that are unforced (adiabatic and quasi inviscid; Schubert et al 1999;Kossin and Schubert 2001;Nolan andMontgomery 2000, 2002;Terwey and Montgomery 2002;Rozoff et al 2006;Kwon and Frank 2005;Hendricks et al 2009;Hendricks and Schubert 2010;Menelaou et al 2013a). These studies provided a basic understanding of barotropic instability and vorticity mixing in the inner core, but a lack of diabatic effects was these studies' primary limitation.…”

“…These studies provided a basic understanding of barotropic instability and vorticity mixing in the inner core, but a lack of diabatic effects was these studies' primary limitation. On the other end of the spectrum, full-physics modeling studies have also been conducted examining eyewall evolution with the inclusion of diabatic and frictional effects (Chen and Yau 2001;Yau et al 2004; Kwon and Frank 2008;Yang et al 2007;Wu et al 2009;Nguyen et al 2011;Menelaou et al 2013b). Wu et al (2009) examined the eyewall evolution for a landfalling typhoon, and investigated the roles of condensational heating and friction on the eyewall evolution.…”

The Generation and Maintenance of Hollow PV Towers in a Forced Primitive Equation Model

“…The instability of the eyewall, its breakdown, and the subsequent PV mixing has been examined extensively in idealized numerical modeling frameworks that are unforced [1][2][3][4][5][6][7][8][9][10]. These studies provided a basic understanding of barotropic instability and vorticity mixing in the inner core, but diabatic effects were ignored in these studies.…”