Slowing winds?

[sinimod]

There is a recent AP article http://news.yahoo.com/s/ap/20090610/...inishing_winds and discussion in RealClimate about the possibility of winds slowing down, possibly due to global warming. From the article:

"It also makes sense based on how weather and climate work, Takle said. In global warming, the poles warm more and faster than the rest of the globe, and temperature records, especially in the Arctic, show this. That means the temperature difference between the poles and the equator shrinks and with it the difference in air pressure in the two regions. Differences in barometric pressure are a main driver in strong winds. Lower pressure difference means less wind."

How ironic it would be if one of the major alternative sources of energy humanity could tap to replace fossil fuels, is being degraded by the main atmospheric effect of fossil fuel use: global warming.

[sinimod]

Here is a link to Pryor et al., 2009, "Wind speed trends over the contiguous USA:

http://php.indiana.edu/~spryor/Paper...8JD011416R.pdf

[sinimod]

Despite the somewhat pessimistic view of Pryor et al. (2009), that we are losing measurable amounts of wind energy, Lu et al. (2009) have a much more upbeat assessment. In their abstract they state "The analysis indicates that a network of land-based 2.5 megawatt (MW) turbines restricted to non-forested, ice-free, nonurban areas operating at as little as 20% of their rated capacity could supply >40 times current worldwide consumption of electricity, >5 times total global use of energy in all forms. Resources in the contiguous United States, specifically in the central plain states, could accommodate as much as 16 times total current demand for electricity in the United States." (http://www.pnas.org/content/early/20....full.pdf+html)

Coupling rapidly evolving wind technology with recent advances in solar technology (http://web.mit.edu/newsoffice/2008/oxygen-0731.html, http://news.softpedia.com/news/Cheap...is-51372.shtml, http://news.nationalgeographic.com/n...arplastic.html, http://www.technologyreview.com/energy/17774/), and the growing political will to make changes in energy production (Waxman Markey Bill), perhaps the worst scenarios of global warming can be avoided.

[sinimod]

Originally Posted by sinimod

Here is a link to Pryor et al., 2009, "Wind speed trends over the contiguous USA:

http://php.indiana.edu/~spryor/Paper...8JD011416R.pdf

I guess that link doesn't work. Here is a link to a summary of the study:

http://www.iop.org/EJ/article/1755-1...6-46ea44da8dfd

[wibble]

Originally Posted by sinimod

"The analysis indicates that a network of land-based 2.5 megawatt (MW) turbines restricted to non-forested, ice-free, nonurban areas operating at as little as 20% of their rated capacity could supply >40 times current worldwide consumption of electricity, >5 times total global use of energy in all forms. Resources in the contiguous United States, specifically in the central plain states, could accommodate as much as 16 times total current demand for electricity in the United States." (http://www.pnas.org/content/early/20....full.pdf+html).

Need more sources to back this up. If true (and I don't doubt it) then it seems pretty clear that the problem is simple inertia in our current society.

[sappha58]

Originally Posted by sinimod

Here is a link to Pryor et al., 2009, "Wind speed trends over the contiguous USA:

http://php.indiana.edu/~spryor/Paper...8JD011416R.pdf

Here's a better link: http://php.indiana.edu/~spryor/Paper...08JD011416.pdf

[sinimod]

Originally Posted by sappha58

Here's a better link: http://php.indiana.edu/~spryor/Paper...08JD011416.pdf

Just now getting around to thanking you for that link, sappha.

[sinimod]

In their recent paper The impact of global warming on the tropical Pacific Ocean and El Niño Collins et al., (2010) state

The tropical easterly trade winds are expected to weaken; surface ocean temperatures are expected to warm fastest near the equator and more slowly farther away; the equatorial thermocline that marks the transition between the wind-mixed upper ocean and deeper layers is expected to shoal; and the temperature gradients across the thermocline are expected to become steeper.

Vecchi et al 2006 stated in their paper that

Observed Indo-Pacific sea level pressure reveals a weakening of the Walker circulation. The size of this trend is consistent with theoretical predictions, is accurately reproduced by climate model simulations and, within the climate models, is largely due to anthropogenic forcing.

They further state

Atmosphere-ocean conditions in the equatorial pacific have changed since the mid-nineteenth century: there has been a significant slowdown of atmospheric circulation, which models indicate has driven a response in ocean circulation. The observed trend in the Pacific surface zonal SLP (sea level pressure) gradient is unlikely due to natural variability.

Ashok and Yamagata, 2010 stated

Patterns of sea-surface warming and cooling in the tropical Pacific seem to be changing, as do the associated atmospheric effects. Increased global warming is implicated in these shifts in El Niño phenomena.

As the ENSO quasi-cycle is dependent on the strength of trade winds, and trade winds are somewhat dependent on the strength of Walker circulation (stronger Walker circulation favors stronger trade winds which induce La Niña conditions, and the opposite for El Niños), it seems that global warming would favor an increase in the occurrence of El Niños and a decrease in the occurrence of La Niñas. Since the globe tends to be warmer during El Niños and cooler during La Niñas, it would seem logical to assume that this scenario would contribute to the enhancement of global warming. However, the shoaling of the thermocline could be a strong mitigating factor in this by allowing cold waters below the thermocline closer to the surface. The steepening of temperature gradients tend to strengthen stratification making ocean water more resistant to upwelling, which would appear to cause more resistance to upwelling along the west coast of the Americas, which should favor normal to El Niño conditions.

Collins et al. go on to say that

Year-to-year ENSO variability is controlled by a delicate balance of amplifying and damping feedbacks, and one or more of the physical processes that are responsible for determining the characteristics of ENSO will probably be modified by climate change. Therefore, despite considerable progress in our understanding of the impact of climate change on many of the processes that contribute to El Niño variability, it is not yet possible to say whether ENSO activity will be enhanced or damped, or if the frequency of events will change.

[sinimod]

I should also mention that the Vecchi et al. study indicated that there has been a 3.5% weakening of Walker circulation since the mid-1800s; and they believe that it will weaken another 10% by 2100. This means the steering of ocean flow by trade winds could decrease by close to 20%.

The Walker circulation, which spans almost half the circumference of Earth, pushes the Pacific Ocean's trade winds from east to west, generates massive rains near Indonesia, and nourishes marine life across the equatorial Pacific and off the South American coast. According to Vecchi "the Walker circulation is fundamental to climate across the globe." "The circulation has been tending to a more El Nino-like state since the 1860s," says Vecchi. "However, the dynamics involved here are distinct from those of El Nino."

So it's complicated.

[776281]

Another factor that has the potential to throw us a curve ball?

[776281]

http://manoa.hawaii.edu/news/article.php?aId=4012

Scientists have long known that atmospheric convection in the form of hurricanes and tropical ocean thunderstorms tends to occur when sea surface temperature rises above a threshold. So how do rising ocean temperatures with global warming affect this threshold? If the threshold does not rise, it could mean more frequent hurricanes. A new study by researchers at the International Pacific Research Center (IPRC) of the University of Hawaiʻi at Mānoa shows this threshold sea surface temperature for convection is rising under global warming at the same rate as that of the tropical oceans. Their paper appears in the Advance Online Publications of Nature Geoscience.

The study notes further that global climate models project that the sea surface temperature threshold for convection will continue to rise in tandem with the tropical average sea surface temperature. If true, hurricanes and other forms of tropical convection will require warmer ocean surfaces for initiation over the next century.

I think this is confirmation of what was expected.

[sinimod]

Falling southern English wind speeds – another problem for the renewables industry

One south of England wind farm faces default on its bank loans because wind speeds have been as low as ever recorded and electricity output has therefore been much less than expected. So far this year the power delivered by the turbines has been less than two thirds of what is predicted in a typical year, meaning is cash flow is failing to meet even the most pessimistic projections. Statistical analysis suggests that electricity output this low should only be achieved once every several hundred years. Another wind farm in southern England reports similar results, with electricity delivery this year so limited that it would only be expected once a century. 2009’s figures were almost as bad.

These wind levels may just be exceptional – the unprecedented persistence of Artic high pressure over the 2009/10 UK winter certainly reduced typical wind speeds. Some people have suggested that the summer melting of Artic sea ice is affecting wind patterns. It could also be that general meteorological conditions have militated against high winds over the last few years. Or it may that the engineers have simply hugely underestimated the underlying degree of natural annual variability in southern UK winds In other words, the average estimated power outputs for these wind farms are correct over a period of decades, but the chance of the actual number being much higher or much lower in any particular year is significantly greater than has been projected.

As Arctic polar ice continues to shrink, the likelihood of warmer air over the Arctic increases. This increases the likelihood of extreme weather events such as the one described above where average annual wind velocities will substantially decrease, thus affecting the potential for successful generation of electricity from wind energy.

[sinimod]

Land use changes are postulated as a possible mechanism for slowing wind velocities as described in this article: Northern Hemisphere atmospheric stilling partly attributed to an increase in surface roughness.

NatureNews summarizes the findings in a short article.

Increasing amounts of vegetation could be causing up to 60% of a slowing in wind speed across the Northern Hemisphere, according to researchers analysing three decades of wind-speed data in Nature Geoscience1 today.

...researchers cannot tell whether the effect, an average 10% slowdown, will make much difference to wind turbines — the slowing winds measured are at 10 metres above the ground, whereas turbines operate at 50–100 metres up, where there is little global data.

Several previous regional studies looking at the United States, Australia, China and parts of Europe have shown decreasing wind speeds just above the planet's surface. Climate change, afforestation and urban development had been mooted as possible causes. But, says Robert Vautard, at the University of Versailles Saint Quentin in Yvelines, France, "people always said the data were rubbish. There was no quality-controlled global archive of data."

Vautard had expected a study spanning such a large area to show speeds increasing in some areas and decreasing in others. But, he says, "we were surprised to see a very clear trend across the whole Northern Hemisphere". Annual wind speeds had declined at 73% of the stations, dropping by 5–15% over almost all of the land areas examined.

Brian Golding, director of forecasting research at the UK Met Office in Exeter, Devon, says that the observation is interesting. "However," he adds, "the timescales are very short for a meteorological trend — it's entirely possible that the previous 30 years would show a different trend."

Increased vegetation — resulting from ex-agricultural land becoming overgrown, afforestation and changing landscape-management practices — could account for 25–60% of the observed stilling in wind speed, says Vautard.

Vegetation changes did not wholly explain wind-speed changes seen in eastern Europe and China. In central Asia the height of vegetation would have to have tripled to account for the stilling. Vautard admits this is "fairly unrealistic". He suspects that changes in general atmospheric circulation may be more important in these parts of the world than in others.

An increase in urbanization was also suggested as a contribution to the slowing of winds.

As for any effect on power generation, Vautard plans to study trends in wind speed at the height of turbines. "It's not a problem for wind generation at the moment," he says, "but it could be in the future if the trend continues."

[sinimod]

Evidence for a weakening of tropical surface wind extremes in response to atmospheric warming

Gastineau and Soden

Abstract

The changes of extreme winds and its links with precipitation are assessed over the past two decades using daily satellite observations and climate model simulations. Both observations and models indicate a decrease in the frequency of the strongest wind events and an increase in the frequency of light wind events in response to a warming of the tropical oceans. The heaviest precipitation events are found to be more frequent when the tropical oceans warm, but the surface winds associated with these extreme rainfall events weaken. These results add further evidence to suggest that the atmospheric circulation becomes less energetic as the climate warms. It further suggests that the enhancement of the extreme precipitation events is mainly a result of increasing atmospheric water vapor and occurs despite a weakening of the large-scale circulation, which acts to diminish the mass convergence toward the precipitating zones.

A little paradoxical, but in light of this and other research, the way I see it, the amplification of warming at the poles, and warming of the planet in as a whole, promotes a general decrease in wind velocity, but warming sea surface temperatures and increased atmospheric water vapor concentrations promote more intense hurricanes.

[sinimod]

Global warming is one of the factors in wind changes over China

The decreasing wind speed in southwestern China during 1969-2009, and possible causes - Xiaomei et al., 2012

Abstract: “Daily wind speed data from 110 stations in southwestern China were analyzed to determine trends, spatial differences and possible causes. There was a statistically significant decrease of 0.24m/s per decade in the annual mean wind speed during the period 1969-2009. The decreasing trend was faster (0.37m/s/10a) during 1969-2000. Between 2001 and 2009, there was a significant increase. The pattern of seasonal changes was similar. Stations with stronger, significant decreasing trends were mainly on the Xizang Plateau, the Hengduan Mountains and the Yunnan Plateau, and stations with significant increasing trends were mainly in the Sichuan basin, indicating the influence of altitude on wind speed. Surface wind speeds in southwestern China have been affected in recent years by both the changed large-scale atmospheric circulation and regional and global warming, while the weakening surface pressure gradient between high and low latitudinal regions may be an important contributor to the decreased wind speed under the asymmetric warming during 1969-2009. The data indicated a positive correlation between wind speed and sunshine duration suggesting another possible influencing factor. Topographical influences are evident in the higher annual and seasonal trends at summit and intermontane basin stations and the lower trends at valley stations.”