Seasonal and diurnal variation of marine wind characteristics based on lidar measurements

The accurate assessment of marine wind characteristics is receiving increasing attention because of its practical importance in diverse areas. However, the reliable measurement of marine winds is often insufficient mainly because of the limitation of the instrumentation used. In the present study, four year lidar measurement data, recorded continuously from March 2012 to November 2015, are collected at an offshore platform near Lamma Island in Hong Kong, China, to obtain useful marine meteorological information, with a particular interest in the seasonal and diurnal variations of wind speed, wind shear co-efficient (WSC) and veering wind angle. It is shown that the wind speed and Weibull parameters generally exhibit evident monthly variation. The maximum monthly wind speed occurs in February, with values between 7.41 and 8.13 m center dot s(-1)depending on the height, and the monthly minimum occurs in August, with values between 4.66 and 5.27 m center dot s(-1). The Weibull scale parameter shows a similar monthly pattern with wind speed, while the Weibull shape parameter peaks in June. Furthermore, the diurnal pattern of both wind speed and Weibull parameters is closely tied to seasonality. The WSC covering the bottom and top layers of the wind turbine is likewise examined. Larger WSCs are obtained during hotter months, while smaller WSCs are associated with cooler months. The diurnal pattern of the WSC shows reasonable agreement among different seasons, although the magnitude is somewhat different. The veering angle generally increases with height. Its monthly pattern reveals a maximum in May, reaching up to 17.8 degrees within the height of concern. Pronounced monthly and diurnal patterns of veering angles are observed at higher altitudes.