Lidar Measurements of Wind Flow over Complex Terrain

Doppler lidars measurements with high horizontal, vertical, and temporal resolution are well suited to understanding physical processes within the boundary layer and validating wind forecast models. The paper will discuss advances and challenges of scanning Doppler lidar measurements of wind flow over complex terrain during the second DOE sponsored Wind Forecast and Improvement Project (WFIP 2). This 18-month long experiment in the Columbia River Basin area is aimed at improving model forecast of wind flow complicated by mountain terrain, coastal effects, and presence of numerous wind farms in this area. (For detailed information on the scope, objectives, instruments, models and participating organizations in the WFIP2 we refer readers to papers provided by J. Wilczak and J. Olson). This paper will describe lidar scanning techniques developed to capture wind features to better understand atmospheric processes that may help improve accuracy of wind forecast by operational numerical models. The scanning strategy utilizes the ability of lidar to provide data while scanning in conical, vertical-slice, or vertically pointing modes and combines these scans to obtain profiles of wind speed, direction, turbulence, vertical velocity, dissipation rate, and other quantities in real time. In addition to the quantitative analysis of data, lidar scans will help visualize wind flow variability in the surrounding area and reveal wind features such as the low level jet, gap flows exiting the gorge, and trapped lee waves. Deployment of two identical scanning lidars on separated sites along prevalent wind directions presents an opportunity to obtain data upstream and downstream of the local wind farms and analyze their overall impact on wind flow. Preliminary results on lidar data analysis from both sites, captured features of wind flow in complex terrain, along with examples of model validation by lidar data will be presented.