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New measurement technologies provide exciting opportunities to advance understanding of complex flows in the atmospheric boundary layer. The XPIA campaign assessed innovative deployment strategies to offer guidance for future studies.
Wind energy now provides 20% of the electricity in some regions of the United States, with promise to provide far more (Wiser et al. 2015). Individual wind turbines generate power based on the winds entering their rotor disk; similarly, clusters of wind turbines, or wind farms, respond to winds and turbulent characteristics of the atmospheric boundary layer (ABL; Sumner and Masson 2006; Wharton and Lundquist 2012; Vanderwende and Lundquist 2012; Sathe et al. 2013) as well as mesoscale flow features (Cui et al. 2015). In turn, wind farms generate complex local wind flows characterized by increased turbulent mixing, modified wind profiles at wind turbine rotor disk heights, and accelerations beneath wind turbines (Barthelmie et al. 2007; Fitch et al. 2013; Rajewski 2013; Rhodes and Lundquist 2013). These complex flows affect local meteorology and downwind turbines. To optimize wind energy deployment and production, and to assess wind farm impacts, accurate measurements of the complex flows within and around wind farms are required.
Emerging measurement capabilities may provide the capabilities for assessing these complex flows. Avoiding the limitations of fixed meteorological towers, Doppler lidar, radar, and sodar sensing systems have assessed wind turbine inflow and wakes (Käsler et al. 2010; Bingöl et al. 2010; Hirth and Schroeder 2013; Smalikho et al. 2013; Iungo et al. 2013; Aitken et al. 2014; Iungo and Porté-Agel 2014; Aitken and Lundquist 2014; Kumer et al. 2015; Trabucchi et al. 2015; Hirth et al. 2015; Banta et al. 2015); a comprehensive review is given in Clifton et al. (2015). Coordinated measurements with multiple Doppler systems can provide vector winds (Newsom et al. 2008; Hill et al. 2010; Carbajo Fuertes et al. 2014; Berg et al. 2015; Gunter et al. 2015; Klein et al. 2015) in the boundary layer. Microwave radiometers provide frequent high-resolution assessments of temperature stratification to assess atmospheric stability (Ware et al. 2003; Bianco et al. 2005; Cimini et al. 2011; Friedrich et al. 2012). Two-component vector wind fields can be estimated over large areas using a single non-Doppler elastic backscatter lidar (Mayor and Eloranta 2001; Hamada et al. 2016).