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The land surface temperature around the west-central Texas wind farms warmed at a rate of 0.72˚ C per decade during the study period relative to nearby regions without wind farms, an effect most likely caused by the turbulence in turbine wakes acting like fans to pull down warmer air from higher altitudes at night, said lead author Liming Zhou at the University of Albany, State University of New York.Figures 1 and 2 from the report.
The results were published in the April 29 issue of Nature Climate Change. Zhou and colleagues studied land surface temperature data ranging from 2003 to 2011, from the MODIS (Moderate-resolution Imaging Spectroradiometer) instruments on NASA's Aqua and Terra satellites.
Land Surface Temperature is not to be confused with Air Temperature readings which are reported to the National Weather Service by stations. These LST are read by the MODIS spacecraft of the actual surface temperature. The warming observed by MODIS mostly occurred at night. In the Texas region studied, the land surface temperature after sunset typically cools faster than the air temperature. But, as the turbines continued to turn, their movement brought warmer air to the surface and created a warming effect compared to non-wind farm regions.
The researchers caution that the warming applies to this particular region over a time when wind farms were expanding rapidly. The results are not directly applicable for other regions. They should not be extrapolated over a longer period of time. They also note that the warming is a local effect. It would not contribute to a larger global trend adding to global warming. This is not a situation where large amounts of heat are being generated and released into the atmosphere. What is occurring is the mixing of existing heated air.
"This is a first step in exploring the potential of satellite data to quantify the possible impacts of big wind farms on weather and climate," said Chris Thorncroft, a coauthor of the study and chair of the Atmospheric and Environmental Sciences department at University at Albany, State University of New York. "We are now expanding this approach to other wind farms and building models to understand the physical processes and mechanisms driving the interactions of wind turbines and the atmospheric boundary layer near the surface."The U.S. wind industry has 46,916 megawatts of capacity at the end of 2011. This is >20% of the world’s installed wind power. It is 2.9% of electric power in the United States. The U.S. wind industry has added over 35% of all new generating capacity over the past 4 years. These statistics are from the American Wind Energy Association and the Department of Energy. This added capacity during that timeframe is second only to natural gas, and more than nuclear and coal combined.
"Wind power is going to be a part of the solution to the climate change, air pollution and energy security problems," said Somnath Baidya Roy at University of Illinois, Urbana-Champaign, a co-author of the study. "Understanding the impacts of wind farms is critical for developing efficient adaptation and management strategies to ensure the long-term sustainability of wind power."The other authors for this research, which was funded by University of Albany, State University of New York and the National Science Foundation, include Yuhong Tian at IMSG at NOAA/NESDIS/STAR, Lance F. Bosart at the University of Albany, State University of New York, and Yuanlong Hu at Terra-Gen Power LLC, San Diego, Calif.