Dynamics of tilted atmospheric vortices under asymmetric diabatic heating

Abstract

Päschke et al. (J Fluid Mech, 2012) studied the nonlinear dynamics of strongly tilted vortices subject to asymmetric diabatic heating by asymptotic methods. They found, inter alia, that an azimuthal Fourier mode 1 heating pattern can intensify or attenuate such a vortex depending on the relative orientation of the tilt and the heating asymmetries. The theory originally addressed the gradient wind regime which, asymptotically speaking, corresponds to vortex Rossby numbers of order unity in the limit. Formally, this restricts the applicability of the theory to rather weak vortices. It is shown below that said theory is, in contrast, uniformly valid for vanishing Coriolis parameter and thus applicable to vortices up to low hurricane strengths. An extended discussion of the asymptotics as regards their physical interpretation and their implications for the overall vortex dynamics is also provided in this context. The paper’s second contribution is a series of three-dimensional numerical simulations examining the effect of different orientations of dipolar diabatic heating on idealized tropical cyclones. Comparisons with numerical solutions of the asymptotic equations yield evidence that supports the original theoretical predictions of Päschke et al. In addition, the influence of asymmetric diabatic heating on the time evolution of the vortex centerline is further analyzed, and a steering mechanism that depends on the orientation of the heating dipole is revealed. Finally, the steering mechanism is traced back to the correlation of dipolar perturbations of potential temperature, induced by the vortex tilt, and vertical velocity, for which diabatic heating not necessarily needs to be responsible, but which may have other origins.

An Interactive Approach for Identifying Structure Definitions

“…One motivation for the development of the presented tool is the fact that the vortex core line is a major ingredient for the asymptotic theory on strongly tilted TCs (Päschke et al, 2012;Dörffel et al, 2021). The TC core line prescribes the origin of a tilted cylindrical coordinate system and both, symmetric and asymmetric structures, are assessed relative to this origin.…”

“…In this section, we give a clear and concise example of our approach by demonstrating the procedure for specific structures, namely spatio-temporal geometric structures of tropical cyclones (TC), i.e., their vortex cores and centerlines. The example is motivated by a new theory of TC intensification, according to which the inclination of the centerline, in interaction with atmospheric heat patterns that adopt some spatial orientation to the inclined centerlines, is a key parameter for TC intensification (Päschke et al, 2012;Dörffel et al, 2020Dörffel et al, , 2021.…”

“…It is located in or close to the center of the TC vortex and represents another mental concept that is not explicitly described by data fields. Representation of the TC domain in cylindrical coordinates that are centered at the vortex core line is very useful for studying TC structure and dynamics (see (Päschke et al, 2012;Dörffel et al, 2021)). Quantitative results, however, highly depend on a TC core line.…”

Definition, detection, and tracking of persistent structures in atmospheric flows

“…A single tropical cyclone in three spatial dimensions is considered. The data is generated by numerical simulations with the general purpose atmospheric flow model EULAG (for further details see Prusa, Smolarkiewicz, and Wyszogrodzki, 2008;Doerffel et al, 2021). The horizontal grid is chosen to cover 4000 km with 192 grid point in each direction.…”

“…Furthermore, we see that the vortex centerline, as a three-dimensional line feature, evolved non-trivially due to both transport by the external wind and self-induced motions (cf. Päschke et al, 2012;Doerffel et al, 2021, for The time horizon for the computational method is the time interval from 02-Sep-2018 00:00 to 02-Sep-2018 14:00.…”