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Posted at 10:30 AM ET, 07/15/2009

Can Wind Farms Change the Weather?

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Large-scale wind farms, consisting of hundreds to thousands of wind turbines spread over large areas for generating electricity, are likely to play an increasingly important role in providing a climate-friendly source of energy. Unlike power plants that burn oil, coal or natural gas, wind power requires no fuel, emits no pollution and produces no carbon dioxide nor any other greenhouse gas.

The efficiency, effectiveness and economic value of wind power clearly depends critically on the weather, along with factors such as terrain, vegetation and building structures, which affect the speed, direction and variability of the wind striking the blades of wind turbines. But can wind farms, in turn, affect the weather? (Do you really think I'd be writing this post if the answer was "no"?)

Keep reading for more on wind farms and their potential to change weather...

The question might seem far-fetched at first. But think of wind farms, collectively, as huge butterflies in the realm of chaos theory, where a seemingly inconsequential event (e.g., a butterfly flapping its wings) can lead to consequential changes in the sequence of events that follow.

Researchers are investigating the potential for large wind farms in one region to alter weather patterns in another region downwind. Specifically, the turning of the wind mill propellers creates considerable turbulence, which mixes air up and down. The resulting bumpiness of the air could significantly influence winds at low levels of the atmosphere.

"If you have a couple of wind farms over a 10-kilometer patch in the Midwest, that's not going to make some kind of global impact on the weather," said University of Maryland atmospheric scientist Daniel Kirk-Davidoff in a recent Christian Science Monitor story. But if the whole Midwest "is somewhat roughened over a large area, then you could imagine having a large-scale impact on the atmosphere."

Kirk-Davidoff and his UMD colleague, Daniel Barrie, used a global general circulation model of the atmosphere (similar to the models used to predict climate change) to calculate the effects of blanketing the Midwest with a grid of interconnected wind farms with thousands of wind turbines. On average, the study found that wind speeds were lowered by 5.5-6.7 miles per hour immediately downwind. More significantly, the wind turbines caused large-scale disruptions of air currents, which rippled out like waves that appeared to trigger substantial changes in the development and track of storms over the North Atlantic.

The areal coverage and density of wind turbines in the study are admittedly unrealistic. Currently, the largest wind farm in the nation -- and world -- is the Horse Hollow Wind Energy Center in Taylor County, Texas, with 421 wind turbines in operation. However, ultra-large wind farms with thousands of turbines in especially wind-prone parts of Texas and the Midwest are considered within the realm of possibility.

The magnitude and degree of the impact of such wind farms would presumably be less than in the model simulation. But still the consequences, while unintended, could be significant, especially in situations involving storms such as major winter cyclones forming along a strong frontal zone. Ensemble forecasting has shown that even apparently innocuous changes in the low-level wind field can result in large uncertainties in the timing, strength and motion of major storms over a period of just a few days.

What remains unclear is how the impact of wind farms might compare to, for example, the effects of high-rise complexes or, for that matter, the influence of building a whole new city dominated by skyscrapers, such as that occurring at several locations across China. And yes, disturbances of the atmosphere originating in China can and frequently do impact weather systems affecting the United States in the matter of just a few days (to be discussed in a later post).

Wind farms may also result in important changes in local climatology, potentially impacting, for example, agricultural interests located within and immediately around areas encompassed by wind farms. The turbulence induced by the propellers of wind turbines mixes air along with the heat and moisture it contains -- the effects can spread for miles around. This is especially true at night when the disturbed airflow is not masked by the natural turbulence caused by solar heating.

Based on computer modeling, researchers at Duke and Princeton universities found that wind mill-generated turbulence raised pre-dawn surface temperatures by about four degrees and resulted in drier soil conditions. Presumably, the surface warmth was largely the result of the mixed air preventing the settling of cold air at the surface, while the dryness reflected increased evaporation by the wind of soil moisture. This is not dissimilar to the more familiar experience of a windy night keeping temperatures from falling as low as might otherwise be expected and also drying out pavement made wet by an evening shower.

By  |  10:30 AM ET, 07/15/2009

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