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Title: CWEX: Crop/wind-energy experiment: Observations of surface-layer, boundary-layer and mesoscale interactions with a wind farm

Author
item RAJEWSKI, DANIEL - Iowa State University
item TAKLE, EUGENE - Iowa State University
item LUNDQUIST, JULIE - National Renewable Energy Laboatory
item Prueger, John
item HORST, THOMAS - National Center For Atmospheric Research (NCAR)
item Pfeiffer, Richard
item Hatfield, Jerry
item SPOTH, KRISTOPHER - Iowa State University
item DOORENBOS, RUSSELL - Iowa State University

Submitted to: American Meteorological Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/18/2012
Publication Date: 5/5/2013
Citation: Rajewski, D.A., Takle, E.S., Lundquist, J.K., Prueger, J.H., Horst, T.W., Pfeiffer, R.L., Hatfield, J.L., Spoth, K.K., Doorenbos, R.K. 2013. CWEX: Crop/wind-energy experiment: Observations of surface-layer, boundary-layer and mesoscale interactions with a wind farm. American Meteorological Society. 94(5):655-672.

Interpretive Summary: Wind turbines have become common across the landscape of the Midwest. These wind farms occupy large expanses of agricultural lands and there is concern about the potential impact of these turbines on crop production in fields surrounding these turbines. To address the question of the effects of turbines on the air surrounding corn and soybean crops adjacent to turbines, a study was designed to evaluate the effect of turbines on wind flow and temperature patterns upwind and downwind of a wind farm. A range of techniques was used to measure the effect of turbines on temperature and wind patterns affected by the turbines. Turbines caused the wind speed to be reduced downwind of the turbines; however, there was an increased mixing of the air showing that although windspeed was reduced there was more upward motion of the air. This caused the temperatures to be more uniform with height within the wind farm. The implications of these changes in wind and temperature on corn and soybean production have not been studied. These results are of value to scientists in designing future studies to evaluate the impacts of wind turbines on temperature and wind movement surrounding wind farms.

Technical Abstract: Large wind turbines perturb mean and turbulent wind characteristics, which modify fluxes between the vegetated surface and the lower boundary layer. While simulations have suggested that wind farms could create significant changes in surface fluxes of heat, momentum, moisture, and CO2 over hundreds of square kilometers, little observational evidence exists to verify these impacts. Quantifying the influences of the “turbine layer” is needed to quantify how surface fluxes are modified and to better forecast energy production by a wind farm. Changes in fluxes are particularly important in regions of intensely managed agriculture where crop growth and yield are highly dependent on subtle changes in moisture, heat, and CO2 fluxes. Furthermore, speculations abound of possible mesoscale consequences of these boundary-layer changes produced by wind farms. To address the lack of observations for addressing these questions, we developed CWEX as a multi-agency, multi-university field program in central Iowa. Summer-long flux observations in 2010 documented surface flux variability within a wind farm, and a two-week deployment of a vertically pointing lidar quantified wind profiles. In 2011, we expanded this test site, with the deployment of six flux stations and multiple wind-profiling lidars to document turbine wakes. The results of these experiments provide valuable insights in the exchanges over a surface modified by wind turbines and provide a base for a more comprehensive measurement program planned for summer 2013.