Intensification of Strongly Tilted Tropical Vortices Through Asymmetric Diabatic Heating

Although much effort was made to understand the dynamical behavior of tropical cyclones key mechanism of rapid intensification are not fully captured, yet.

Our investigations concern intensification mechanisms of tilted atmospheric vortices with Rossby number of order 1 and higher as they are observed by Huntley and Diercks (1981), Mon. Weather Rev. vol. 109, 1689 - 1700 and Dunkerton et al. (2009), Atmos. Chem. Phys. vol. 9, 5587 - 5646, among other. Along the lines of Päschke et al. (2012), JFM vol. 701, 137 - 170, we study the influence of strong vortex centerline displacements of the order of the radius of maximum wind, i.e., ~ 100 km, and the alignment of asymmetric diabatic heat release relative to the tilt direction. Examination of the governing equations for dry-air inviscid flows with diabatic sources by multiscale asymptotic analysis leads to an effective evolution equation for the circumferential velocity depending only on tilt and heating pattern. This model gives rise to a possible connection between moisture-induced asymmetric latent heat release and rapid intensification of a tilted tropical cyclone which is in agreement with observations. Furthermore, this theory is compatible with Lorenz’ concept of APE revealing the mechanism of transferring heat into kinetic energy.

We present an outline of the theory for the asymmetrically-driven diabatic amplification from tropical storm to hurricanes strength. Three-dimensional simulation of externally heated dry-air atmospheric flows corroborate the theoretical predictions. Concluding remarks will highlight the track of future investigations, especially those of moisture-driven thermodynamical effects. See also the companion talk given by R. Klein who will highlight recent developments of incorporating moist thermodynamics and boundary layer dynamics into the discussed asymptotic theory.