Wind characteristics over different terrains

• Fractal dimension values of wind speed, temperature, and pressure are calculated and periodicity of them is observed.
• Gust factors of wind speed during tropocal cyclones and strong monsoons are studied by considering the strength effect.
• GEV function is found accurate to depict the wind gust; predictors using its position parameter is provided.
• Wind turbulent characteristics under different terrains are compared based on long-term field measurements.

This paper presents an investigation of wind characteristics over several typical terrain conditions based on a 6 years’ database from four surface meteorological stations in Hong Kong. Basic weather elements such as wind speed, air temperature, and air pressure are discussed first to present an overall description of the regional climate. Fractal dimension is introduced to quantify the fluctuations of these weather elements. Wind quantities are presented and discussed subsequently, which mainly include turbulence intensity, gust factor, spectra, and turbulence integral length scale. Gust factors under different terrain conditions such as open sea terrain and hilly terrain, and in high wind events such as tropical cyclones and monsoons are discussed, and the associated comparative study is conducted. The analyzed results from tropical cyclones and monsoons under neutral conditions demonstrate little difference. The relationship between gust factor and turbulence intensity is studied and fitted by a linear model, in which the peak factor is found to be 3.1. Gust-duration dependence of gust factor values is also investigated. Two kinds of empirical models are presented for open sea and built-up exposures. The von Karman spectrum is found to be suitable to depict the energy distributions in low frequency range. Based on the spectral analysis results, turbulence integral length scale and standard deviations of fluctuating wind speeds are estimated and discussed. The findings of this comprehensive study can be used as references for wind loading estimation, wind energy assessment and air pollution prevention over different terrains.