11D.1
Small-scale inner core structures and wind streaks in a simulated hurricane
M.K. Yau, McGill University, Montreal, QC, Canada; and Y. Liu, D. L. Zhang, and Y. Chen
The objectives of this paper are to present simulation results of the fine-scale features of Hurricane Andrew (1992) using a cloud-resolving grid length of 2 km and to diagnose the formation of small-scale wind streaks. As compared to observations and a previous 6-km model run, our results show that a higher resolution produced significant improvements in the structures and evolution of the inner-core eyewall and spiral rainbands, and in the organization of convection. The eyewall becomes much more compact and symmetric, with its width decreased by half, and the radius of maximum wind is reduced by ~10 - 20 km. A deep and intense potential vorticity (PV) zone is formed at the edge of the eye. A ring of maximum PV is collocated in regions of maximum upward motion in the eyewall and interacts strongly with the eyewall convection. The convective cores in the eyewall are associated with small-scale wind streaks. The formation of the wind streaks is diagnosed from an azimuthal momentum budget. The results reveal small-scale Lagrangian acceleration of the azimuthal flow. It is found that at the lowest model level, the main contributor to the Lagrangian azimuthal wind tendency is the radial advection of angular momentum per unit radius. At an altitude of 1.24 km, vertical advection of the azimuthal wind, in addition to the radial advection of angular momentum per unit radius, plays important roles.
Session 11D, tropical cyclone observations and structure VI
Wednesday, 5 May 2004, 3:45 PM-5:15 PM, Napoleon III Room
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