Observations of vertical wind profiles of tropical cyclones at coastal areas: Fid-Bau Portal

Observations of vertical wind profiles of tropical cyclones at coastal areas

He, Y.C. / Chan, P.W. / Li, Q.S.

Abstract Vertical wind profiles of tropical cyclones (TCs) below 5000m with marine and rugged exposures are investigated based on synchronized measurements from Doppler radar wind profilers and anemometers at three coastal meteorological stations in Hong Kong. The dependence of TCs׳ mean wind structure on storm-relative position, wind strength and exposure is discussed in the context of both case study and composite analysis. For onshore winds, it is found that the wind speed profiles follow the logarithmic-law below about 400m, and the mean wind veers logarithmically with height throughout the Ekman layer. Moreover, the roughness length scale reaches a maximum value and then decreases with increasing wind speed. As the exposure transforms from a marine type to rugged terrains, the mean wind structures vary markedly, featured by a stronger wind shear in a deepened boundary layer. The low-level jets of mean speed profiles are observed in the range of 330–1600m and tilt outward with height. The gust factor of surface wind and the maximum wind scaled by a layer mean wind speed vary with the storm-relative position as well. The obtained profiles also reveal the occasional existence of a secondary maximum wind near 3000–3500m that is accompanied with more turbulent surface wind.

Highlights • Vertical wind profiles of tropical cyclones below 5000m with marine and rugged exposures are investigated. • The investigation is based on measurements of 8 years from both anemometers and wind profilers during tropical cyclones. • Both case studies and composite analyses are conducted.