Abstract：Offshore wind energy resources are more abundant than on land. However, sea and land winds have different meteorological elements so offshore wind resource assessments need to take the impact of the temporal and spatial characteristics of the offshore wind resources into consideration. Data from an offshore wind measurement mast was used to study offshore wind distributions at different time scales. The EM (expectation-maximization) algorithm was used to study the differences in offshore wind distributions between day and night, which is normally not considered in traditional wind assessment methods. The spatial characteristics of offshore winds will than analyzing using a machine learning algorithm, Monin-Obukhov similarity theory, and a parameter replacement scheme in discrete calculations and in an ocean surface aerodynamic roughness model. This method efficiently reflects the impact of ocean surface aerodynamic roughness changes on the vertical variations of the wind speed that is not considered in traditional wind shear formula. The results show the temporal and spatial characteristics of the offshore wind resources as a basis for better offshore wind assessments for planning offshore wind farms.
 赵燕华, 蒋翠花, 吴杰. 宿迁70m高度测风塔风速和风能的变化特征分析[C]//S8大气探测与仪器新技术、新方法. 北京:中国气象学会, 2012:349-353. ZHAO Yanhua, JIANG Cuihua, WU Jie. Analysis of characteristics of wind resource based on 70-meter wind measurement mast in Suqian[C]//S8 New Technology and Method of Atmospheric Detection and Instrument. Beijing:Chinese Meteorological Society, 2012:349-353. (in Chinese)
 符平, 秦鹏飞, 张金接. 海上风资源时空特性研究[J]. 中国水利水电科学研究院学报, 2014,12(2):155-161. FU Ping, QIN Pengfei, ZHANG Jinjie. Research of spatio-temporal characteristics of offshore wind resources[J].Journal of China Institute of Water Resources and Hydropower Research, 2014,12(2):155-161. (in Chinese)
 李常春. 风资源评估方法研究[D]. 呼和浩特:内蒙古工业大学, 2006. LI Changchun. Study on the Method of Wind Resource Assessment[D]. Huhhot:Inner Mongolia University of Technology, 2006. (in Chinese)
 杜燕军, 冯长青. 风切变指数在风电场风资源评估中的应用[J]. 电网与清洁能源, 2010(5):62-66. DU Yanjun, FENG Changqing. Application of wind shear index in the assessment of wind resources of wind farm[J].Power System and Clean Energy, 2010(5):62-66. (in Chinese)
 王有禄, 李淑华, 宋飞. 风电场测风数据的验证和处理方法[J]. 电力勘测设计, 2009,16(1):60-66. WANG Youlu, LI Shuhua, SONG Fei. Treatment method and inspection of anemometric dates in wind power plant[J].Electric Power Survey and Design, 2009,16(1):60-66. (in Chinese)
 Businger J A, Wyngaard J C, Izumi Y, et al. Flux-profile relationships in the atmospheric surface layer[J].Journal of the Atmospheric Sciences, 1971,28(2):181-189.
 Gryning S E, Batchvarova E, Brümmer B, et al. On the extension of the wind profile over homogeneous terrain beyond the surface boundary layer[J].Boundary-Layer Meteorology, 2007,124(2):251-268.
 Venkatram A. Estimating the Monin-Obukhov length in the stable boundary layer for dispersion calculations[J].Boundary-Layer Meteorology, 1980,19(4):481-485.
 Lange B, Larsen S, Højstrup J, et al. Importance of thermal effects and sea surface roughness for offshore wind resource assessment[J].Journal of Wind Engineering & Industrial Aerodynamics, 2004,92(11):959-988.
 H gstr m U L F. Non-dimensional wind and temperature profiles in the atmospheric surface layer:A re-evaluation[J]. Boundary-Layer Meteorology, 1988,42(1-2):55-78.
 Charnock H. Wind stress on a water surface[J].Quarterly Journal of the Royal Meteorological Society, 1955,81(350):639-640.
 Smith S D. Coefficients for sea surface wind stress, heat flux, and wind profiles as a function of wind speed and temperature[J].Journal of Geophysical Research:Oceans, 1988,93(C12):15467-15472.