Intensification of tilted atmospheric vortices by asymmetric diabatic heating
Päschke et al. (JFM, 701, 137--170 (2012)) studied the nonlinear dynamics of strongly tilted vortices subject to asymmetric diabatic heating by asymptotic methods. They found, \ia, that an azimuthal Fourier mode~1 heating pattern can intensify or attenuate such a vortex depending on the relative orientation of tilt and 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 in the near equatorial region. 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. In addition, the paper presents an extended discussion of the asymptotics as regards their physical interpretation and their implications for the overall vortex dynamics. The paper's second contribution is a series of three-dimensional numerical simulations examining the effect of different orientations of dipolar heat release on idealized tropical cyclones. Comparisons with numerical solutions of the asymptotic equations yield evidence that supports the original predictions. In addition, the influence of asymmetric diabatic heat release on the time evolution of centerline tilt is analysed further, and a steering mechanism based on the orientation of the heating dipole is revealed.