JP1.39
Parameterized wind gusts associated with a severe landfalling tropical cyclone
Hamish A. Ramsay, CIMMS/Univ. of Oklahoma, Norman, OK; and L. M. Leslie and M. L. M. Wong
Wind gusts associated with landfalling tropical cyclones are responsible for the majority of wind-related damage to structures. These localized very high wind speeds originate above the surface layer, generally in the lowest 500 m, and are transferred to the surface by convective downdrafts and/or mechanically-induced turbulence. The very small space and time scales of these gusts means that even the most sophisticated numerical simulations have difficulty reproducing them explicitly. Consequently, several wind gust parameterization techniques have been developed, though their application to tropical cyclones has been limited. The current study employs a mesoscale model to investigate wind gusts associated with severe tropical cyclone (TC) Larry (2006) over northeastern Australia using two wind gust parameterization schemes: (i) Brasseur's WGE method, and (ii) a scheme used by the New Zealand Met. Service. A quadruply nested grid with grid spacings of 27 km, 9 km, 3 km, and 1 km is used for domains 1 to 4 respectively. Very high-resolution terrain data (~ 900 m ) is used in domain 4 to explore the interaction between the TC winds and the underlying complex terrain. A second experiment is performed in which the terrain is removed completely to investigate the TC boundary layer over flat land. Preliminary results suggest that TC wind gusts are regulated by both the maximum wind speed in the lowest 1000 m and the characteristics of the underlying terrain. Very high gust ratios (maximum wind gust/ 10m wind) are found in the lee of steep terrain. Maximum wind gusts, with speeds of up to 300 km/hr, occur over topographic ridges as well as regions of strong convection close to the TC eye. In addition to the parameterized wind gusts, an analysis of the near-surface wind field in the 1 km domain over flat land reveals fine-scale banding features that appear to be driven by strong vertical wind shear within the TC boundary layer. The physical mechanisms behind these bands are still being investigated.
Joint Poster Session 1, Tropical Cyclones and Probability/Statistics Posters
Monday, 21 January 2008, 2:30 PM-4:00 PM, Exhibit Hall B
Previous paper Next paper