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Wind and Structures Volume 19, Number 3, September 2014 , pages 249-270 DOI: https://doi.org/10.12989/was.2014.19.3.249 |
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Wind characteristics observed in the vicinity of tropical cyclones: An investigation of the gradient balance and super-gradient flow |
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K.T. Tse, S.W. Li, C.Q. Lin and P.W. Chan
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| Abstract | ||
| Through comparing the mean wind profiles observed overland during the passages of four typhoons, and the gradient wind speeds calculated based on the sea level pressure data provided by a numerical model, the present paper discusses, (a) whether the gradient balance is a valid assumption to estimate the wind speed in the height range of 1250 m ~ 1750 m, which is defined as the upper-level mean wind speed, in a tropical cyclone over land, and (b) if the super-gradient feature is systematically observed below the height of 1500 m in the tropical cyclone wind field over land. It has been found that, (i) the gradient balance is a valid assumption to estimate the mean upper-level wind speed in tropical cyclones in the radial range from the radius to the maximum wind (RMW) to three times the RMW, (ii) the super-gradient flow dominates the wind field in the tropical cyclone boundary layer inside the RMW and is frequently observed in the radial range from the RMW to twice the RMW, (iii) the gradient wind speed calculated based on the post-landfall sea level pressure data underestimates the overall wind strength at an island site inside the RMW, and (iv) the unsynchronized decay of the pressure and wind fields in the tropical cyclone might be the reason for the underestimation. | ||
| Key Words | ||
| boundary layer height; field measurements; gradient balance; super-gradient feature; typhoon mean wind profile | ||
| Address | ||
| K.T. Tse and C.Q. Lin:Department of Civil and Environmental Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong S.W. Li: CLP Power Wind/Wave Tunnel Facility, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong P.W. Chan: Hong Kong Observatory, 134A Nathan Road,Kowloon, Hong Kong | ||