Extended Abstract (48K)4A.5
The comparative effects of frictional convergence and vertical wind shear on the asymmetries of a hurricane
Hongyan Zhu, University of Munich, Munich, Germany; and R. K. Smith
A minimal three-dimensional hurricane model formulated on an f-plane is used to investigate the asymmetries that develop when a model storm is subjected to ambient vertical wind shear.
The asymmetries that develop in the moist version of the model have different structure to those that develop in a dry version. In the former case there are two competing factors that influence the asymmetric structure of inner core: vertical wind shear and boundary layer frictional convergence. The asymmetries are different in the different stages of development, and also different in the core region compared with the outer region of the vortex.
The moist experiments with 5 m/s easterly environment shear shows that in the developing stage, the shear flow influences the vertical velocity and temperature anomaly distribution above the boundary layer. After the rapid intensification, when the saturation occurs in the core, the vortices in the upper layer and lower layer are strongly coupled, and there is no obvious tilt in the core region. Therefore, in the mature hurricane, the boundary layer frictional convergence dominates the effects induced by the shear flow on the asymmetries in the vortex center. However, the inner core of the vortex remains upright whilst the outer regions are more strongly tilted. The maximum vertical velocity above the boundary layer outside of core region has different distribution from that in the core region and is mainly influenced by the tilt of the outer region of the center instead of the boundary layer friction.
Session 4A, Tropical Cyclones and Vertical Shear
Monday, 3 May 2004, 3:45 PM-5:30 PM, Le Jardin Room
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