“Sufficiently Potent to Redirect Present Currents” • Watts Up With That?

From the NoTricksZone

By P Gosselin

Wind Turbines are causing climate change

Hat-tip: Klimanachrichten here

It’s ironic: Man is changing the environment and climate in order to prevent change.

Atmospheric wakes extending from the bottom to the top of the picture [contains modified Copernicus Sentinel data (Sentinel 2A-MSI 29/03/2021), processed by ESA & Hereon/ Dr Martin Hieronymie]

Researchers from the Hereon Helmholtz-Zentrum have found shifts in airflows and sea currents, which are connected to offshore wind farms.

A team led by Nils Christiansen recently published a research paper about the impacts offshore wind farms have on the ocean dynamics, published in the journal Frontiers in Marine Science. Press release here.

“Wind speed deficits spread up to 70 km behind the wind farms”

The turbines extract kinetic energy from the wind field to generate electricity. Downwind of the wind turbines, the so-called atmospheric wakes develop, and are characterized by reduced windspeed, specific pressure conditions and enhanced air turbulence. During stable atmospheric circumstances, the wind speed deficits spread up to 70 km behind the wind farms.

Using high-resolution hydrodynamic computer simulations, the team analyzed the effects on the southern North Sea for the summer of 2013 (May to September). The analysis shows a link between atmospheric wakes and transformation in the momentum-driven exchange between the atmosphere and water. As a consequence, the horizontal currents and the stratification of the water could be affected.

Redirecting existing currents

The wake effects are sufficiently potent to redirect the existing currents, and thus results in shifting mean temperatures and a changed salinity distribution in the wind farm areas.

“While the occurring changes remain within the range of interannual variability, they illustrate similar magnitudes as the presumed mean changes due to climate change or year-to-year variability,” says Nils Christiansen, from the Hereon Institute for Coastal Systems, who was lead author on the study.

Reduced water surface turbulence

Another wake effect is the reduction of shear-driven processes at the sea surface. In other words, the turbulent mixing of the water surface caused by shear wind is reduced dozens of kilometres around the wind farm. Water is usually stratified, thus a layer of warmer water may lie on top of a layer with cold water. Wind farms disturb this natural stratification. Due to reduced mixing, a stabilized stratification of the water is fostered. This phenomenon was particularly noticeable during the decline in summer stratification.

The natural stratification of the water is especially prominent in summer and decreases towards autumn. In the area of the wind farms, however, a stabilized stratification outside the seasonal variation was measured.

“The magnitude of the induced mean changes does not indicate severe local effects, however far-reaching structural changes in the system occur“, says Christiansen.

“Far-reaching structural changes in the system”

“The transformation concerning currents and mixing are likely to affect plankton production and the food web structure. As a result it may influence the function of protected areas. Hence it is important to consider these consequences while developing marine protection concepts“, says Hereon Institute Director Prof. Corinna Schrum.

Moreover, possible feedbacks on air-sea exchange potentially affects regional atmospheric conditions and ecosystem dynamics.

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