26th Conference on Hurricanes and Tropical Meteorology


Idealised modelling of tropical cyclones in vertical shear: the role of saturated ascent in the inner core

Richard Patra, University of Munich, Munich, Germany

The negative influence of vertical shear of the horizontal wind on the intensity of a tropical cyclone is well documented. The mechanisms responsible for the intensity decrease are less well understood. Numerical calculations with idealised models have indicated that the asymmetric vertical circulation that develops when the inner-core of a tropical cyclone is influenced by vertical shear is important for the evolution of the tropical cyclone. However, there are differences between the results of dry studies and studies using full-physics models. These differences are not well understood. This study seeks to bridge the gap between the dry and full-physics studies by using a simplified representation of latent heat release in saturated flow in the inner-core of a tropical cyclone.

The results show how the vertical circulation changes as the stability of the inner-core decreases and the Rossby penetration depth increases. It is shown that it is not sufficient to interpret the results in terms of a diabatically reduced Rossby penetration depth but that it is necessary to take the diabatic modification of PV into account. Confining diabatic heating only to regions of ascent leads to an intensification of the vortex at lower levels and a decay of the vortex at upper levels. A significant difference is found between the vortex evolution in cases representing weak or strong tropical cyclones.

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Session 4A, Tropical Cyclones and Vertical Shear
Monday, 3 May 2004, 3:45 PM-5:30 PM, Le Jardin Room

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