Gavin Schmidt and Michael Mann
There was an interesting AP story this week about possible changes in wind speed over the continental US. The study (by Pryor et al (sub.)), put together a lot of observational data, reanalyses (from the weather forecasting models) and regional models, and concluded that there was some evidence for a decrease in wind speeds, particularly in the Eastern US. However, although this trend appeared in the observational data, it isn’t seen in all the reanalyses or regional models, leaving open a possibility that the trend is an artifact of some sort (instrumental changes, urbanization etc.). If the effect is real though, one would want to see whether it could be tied to anything else (such as forcing from greenhouse gas or aerosol increases), and indeed, whether it had any implications for wind-generated electricity, water evaporation etc.
Amusingly, both of us were quoted in the story as having ostensibly conflicting views. Mike was quoted as finding the evidence for a trend reasonably convincing, while Gavin was quoted as being unconvinced of the evidence for an anthropogenic climate change signal (note that the two statements are not in fact mutually inconsistent). As one should expect in any news story, these single lines don’t really do justice to the longlonger interviews both of us gave the reporter Seth Borenstein. So what is the bigger context?
First some background. It’s important to note that ‘windiness’ is not a globally uniform field, and that changes will occur in different regions for very different reasons. Also, note that mean wind speed is not the same as storminess*.
Winds in the mid-latitudes are a function of the jet stream and of the ‘baroclinic instability’ that we see as low-pressure systems. In the tropics, winds locally depend strongly on convective activity and on a larger scale, the Hadley circulation. In monsoonal regions (West Africa, India etc.), winds are a function of the temperature contrasts over land and sea during the warm seasons. Winds can be affected by the ozone hole in the Southern Ocean, a change in the orbit of the Earth in the tropics, or by the presence or absence of an ice sheet. So the concept of winds changing in a general sense is not unusual or unexpected. However, because of the many distinct influences you wouldn’t expect all winds to increase or decrease together.
In the free atmosphere off the equator, wind is essentially ‘geostrophic’ which means that it’s driven by the (predominantly north-south) gradients in air pressure, and follows contours of constant pressure (’isobars’). Near the surface, friction slows the winds, and causes them to cross the isobars from high to low pressure (hence we get ‘convergence’ in the center of surface low pressure regions). Nonetheless, changes in surface winds will follow approximately from the associated change in the surface pressure field.
The business-as-usual projections show a general poleward shift of the current subtropical surface high pressure belt into the mid-latitudes, especially during summer (a poleward shift of the descending branch of the so-called “Hadley Cell”). The high pressure belt is a region of low pressure gradient, and hence low wind. A northward shift displaces the region of maximum westerly surface winds poleward, from the U.S. into, say, southern Canada. A decrease in the mean strength of the surface westerlies over the U.S. would therefore appear to be consistent with projected changes in large-scale circulation. However, it’s not that simple. The average wind speed at these latitudes depends as much on the day-to-day variance (driven primarily by mid-latitude storms) as it does on the mean strength of the climatological westerly surface winds. The gradient in temperature between subtropics and pole tends to decrease with global warming (due to the ‘polar amplification’ of warming) and this, in turn, diminishes the “baroclinicity” of the atmosphere, and thus, the degree of storminess. So both a decrease in baroclinicity and a poleward shift in the extratropical band of westerly surface winds would therefore seem to work in the direction of decreasing wind in mid-latitudes.
But even this reasoning is somewhat questionable, as wind anomalies over a region as small as the U.S. are unlikely to be representative of the trend for the entire latitude band on the whole. Factors such as El Nino, and the “Northern Annular Mode” have an important role on wind patterns over the U.S., and changes in the behavior of these phenomena could easily overwhelm the average trend for the mid-latitude band. So in short, the observations of decreasing wind speeds over the U.S. are in a rough sense consistent with these ideas, but given the uncertainties in factors that are important in determining wind patterns over the scale of the U.S. continent, it’s hard to say precisely what would be expected.
Figure 1. The trends in the station winds and in the N. American reanalysis (from fig.4 in Pryor et al.)
In the specific case of the GISS-ER model, we can easily see what the model suggests. The picture below gives the annual mean wind speed change for a business-as-usual scenario out to 2100 (we picked this just because the changes are large, but a picture for simulated trends over the last 50 years is similar).
The first thing to note is that the expected changes are complex. There is a clear increase in the Southern Oceans (related to changing temperature trends in the lower stratosphere associated with both the ozone hole and greenhouse gas increases). There is also a change near the equator associated with increases in convective activity and a shift in the Hadley Cell. Note also that changes over land are very small, and in particular, over the US no significant changes are seen. The situation might be different in different models (or different seasons, or in the day-to-day variance), and so one wouldn’t want to read to much into this single figure, but it makes clear that a change in US windiness is not a strong ‘a priori’ expectation from global warming. This doesn’t of course shed any light on whether the observed trends are real, but it does speak to the attribution part of the discussion.
Indeed, you would need a careful detection/attribution analysis to see if the observed changes in wind speeds are consistent with the multi-model climate change projections. This has been done for surface temperature, precipitation, and sea level pressure changes, and there is no obvious reason it can’t be done for wind speeds if the data holds up.
Regardless of the cause of the indicated decline, is this likely to have a direct impact on wind power generation? There is a study by Archer and Jacobson that explores the potential for wind power over the US, and the results can be seen in this graph:
Wind speed class 3 (usable for power generation) and above (dark blue, green, yellow, red and black dots) are not that widespread, and are concentrated over the plains and offshore. Comparison to the trend map in the Pryor et al study (figure 1 above) shows only a limited overlap, so even if all these sites were being used, it’s not clear the trends would hamper wind-power generation much. However, this is highly speculative and will need to be looked at much more carefully in future.
Whether the wind of change is truly blowing through this continent remains to be seen…
Note that an apparent quote from David Deming that the possibility of decreased wind speed over the Eastern US is somehow in contradiction with the possibility of increased tropical storm intensity in the tropical Atlantic is embarrassing in the inappropriateness of the comparison.
Isn’t the normal sequence of events begin with publication of the paper in question? How are we supposed to evaluate it if we can’t look at what they did? More interestingly, how did this story get legs before publication?
For a more comprehensive global treatment of wind-related issues, see:
Archer & Caldiera 2008, Historical trends in the jet streams, GRL
Here is the general overview of the poleward expansion of the Hadley Cell:
http://ams.confex.com/ams/pdfpapers/124519.pdf
Baroclinic tends to refer to the mid-latitide zone, with cyclone and front-dominated weather patterns, characterized by the mixing of distinct air masses, which is quite unlike the tropics.
Now, the thing to worry about here is that this can result in the development of permanent winter high-pressure zones over the American Southwest, and if you watch the daily pressure maps, you saw that happen this winter at least twice, locking out most early winter storms. Those interior high pressure zones are also the driving force behind Santa Ana winds, which look set to increase (they spill out of high-pressure zones in the Great Basin).
In any case, the notion of a ‘reduced pole-to-equator thermal gradient’ reducing storminess seems specious. It seems more likely to have increased baroclinic instability further north as warm wet air masses will drive farther north earlier in the spring (later in the fall?) and will tend to dump precipitation as water rather than slow. Recall the recent near-flooding of Fargo? Furthermore, recall that it is the gradient in the latent heat of water vapor that provides the central driving force for storms, not temperature gradients. A cold dry air mass mixing with a warm dry air mass produces a little wind, not much else. Add moisture to the warm air mass, you get an explosion.
One other thing about temperatures: For those who haven’t lived in cold weather, cold dry snow at ten degrees below freezing is far, far preferable to wet freezing slush. The dry powder also sticks and generates a nice snowpack for your late summer runoff – the wet slush doesn’t stick around. Freezing rain, on the other hand, destroys orchards, powerlines, etc. That’s an example of how a reduced temperature gradient can wildly change local weather patterns, with devastating results.
Such climatic instability, plus spreading drought, probably represents a much greater threat to agriculture (and thus, to wealthy human civilization) than the temperature change itself.
For more on the runoff issue:
Lundquist, Variability and Trends in Spring Runoff in the Western United States
I saw the earlier article and appreciate the more detailed discussion. I’m certainly not an expert in this area. However, average wind speed probably is not the only thing to crank into the equation on viability of wind power. Some wind sites with lower average speeds are viable because the wind is constant. The turbines can cut in at 9-12 MPH and out at 55 MPH so they can accommodate a variety of conditions. If the speed does decrease it just means the payback period is slightly longer. That may cause a developer a problem if the financing is on a tight payback schedule. However the payback would still only vary between 7-16 years depending on the installation cost. That is quite a bit less than the payback for a nuke or coal plant. Since there is no fuel, pollution control or waste disposal cost associated with wind generated power, the power tends to be cheaper than fossil fuel power very quickly.
For example at Montana’s Judith Gap wind project, the all in costs started out being about 4.9 cents/kWh. That cost includes a number for integrating the wind into the system that is higher than most other places in the world. The utility numbers are likely less than that now because some up front costs have been paid off; integration costs will stablize soon, and renewable energy credits have provided revenue not included in the cost numbers. Including those should reduce the price. The default supply of power for Northwestern Energy, the utility buying wind power from Judith Gap averaged around 6 cents/kwh in 2008. That included the wind and hydro generated power cost to lower the average. I have requested a breakout from the utility and been told they wouldn’t provide it. So bottom line as fossil fuel costs continue to rise, wind will become cheaper than fossil fuel generation even with the 1.5-2.1 cent/kWh production tax credit it enjoys for the first 10 years a project is operational. Also, wind on a system generally creates a reduction in natural gas costs that equates to half cent/kwh. And there are of course the other benefits of no CO2–which would cost 2 to 5 cents/kWh to sequester assuming that sequestration would work.
I figured out how to change our climate with “Underwater Suspension Tunnels”. They can regulate SSTs in deep Western boundry currents such as the Gulfstream current,the Loop current in the GOMEX and the Kuroshio current.By regulating SSTs you then have the ability to regulate climate such as severe weather,tornados,drought and landfalling hurricanes. They also have the ability to produce an enormous amount of electrical energy from the Ke in the deep Western boundry currents at the same time they are busy regulating climate. 13 trillion joules every 7 seconds at each location. They have two phases to them cooling and non-cooling and either phase will produce this electrical energy as well as regulate SSTs and therefore climate. What are your thoughts on this type of climate control.
I completely understand that a newspaper story is an oversimplification. And that you would want to eliminate a false appearance of disagreement between the two of you. however, I would LOVE to see a genuine disagreement. In public. Without pre-vetting.
I like to see this type of analysis of current news items. It helps to keep me current when my High School Chemistry Class mentions something they read on line or in the newspaper.
It is interesting to see your long answer as compared to the one line quote in the original article.
I would like to see articles comparing what climate models predicted 5, 10 and 20 years ago with what is being observed today. Were the predictions low, on target or high? Of course it depends which model run you use.
thank for all the time you guys put in on this blog to inform the rest of us.
Cristina L. Archer says that there is plenty of wind power. NASA says wind is a 15% solution at best. See:
http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=18090
Who slipped several decimal points?
I would encourage you to suspect the data because there are places in east Tennessee where the wind never stops blowing. The mountains in the area cause something much like a vacuum to occur, so the wind is always blowing as it is being pushed over the mountain. Since the mountains stretch along the east coast, some areas near them could be tapped for wind power generation.
The wind power potential map shows very little in the region where I live in the Pacific Northwest, and also in the Columbia basin. And yet not only has it been growing fast, the potential in the eastern parts of these two states is normally said to be very high if only adequate transmission infrastructure can be put in. Where is the disconnect?
Gavin,
The effect of reduced wind speed on generation would really depend on which data set is correct. If the NCDC in situ data is the most accurate (i and j in figures 4 and 5), there would seem to be a significant impact on Midwest wind generation and offshore generation on the East Coast. If NARR data is the most accurate, neither area seems like it would change much. If the NCEP-1 reanalysis is the most accurate, wind speed has been increasing both in the Midwest and the U.S. as a whole!
The paper will certainly be an interesting look at the tricky issue of reconciling conflicting wind data sets, but it seems a tad premature to conclude that there will be any implications for either wind generation or regional climate models.
What might be missing here, especially WRT wind power, is a distinction between global and local winds. If you look at some of the older US (and I presume other) wind projects, you find they’re located where the wind is mostly created by local conditions, as for instance Altamont Pass or the Columbia Gorge, where a pass funnels air between a cool coastal area and a hotter inland one. I don’t think you’d expect much change there?
On the other hand, it seems like winds on the Great Plains & Texas (where a lot of the newer generation is going up) might be driven mainly by global processes, and so would change?
Re 1 –
(PS see my comments 272 to 513 +(in progress, recent hiatus) here: http://www.skepticalscience.com/Arctic-sea-ice-melt-natural-or-man-made.html#1847 , and 76 – 77 here: http://www.skepticalscience.com/argument.php?p=4&t=234&&a=28#1792 )
Near the surface, in the Northern Hemisphere, the general trend with global warming is for the pole to equator temperature gradient to decrease, but of course, not evenly everywhere (by latitude and longitude), and more in winter than summer (it might even be the opposite in summer, I think – specifically I think I’ve seen maps with greater summertime warming of Canada relative to the Arctic ocean).
But aloft, the trend is reversed. Above the tropopause, I think the latitude of greatest warming / least cooling splits into two branches that work there way into the midlatitudes with height – something like that.
(PS in terms of meridional thermal gradients, some similarities between stratospheric ozone loss, volcanic aersol forcing (surface cooling), solar forcing (warming), and greenhouse forcing (tropospheric warming))
The arctic sea ice loss causes winter warming as open water takes longer to freeze in winter due to storage of solar heating in summer, without much actual temperature increase in summer. I would guess this would have the biggest impact on temperature gradients where the summer ice edge is (or was), but of course that’s not accounting for temperature advection patterns. Loss of winter snow cover would have an effect too, though…
But anyway, … I’m still not sure but:
surface temperature trends would tend to reduce storm track activity
upper tropospheric temperature trends would tend to do the reverse
greater water vapor could increase the energy and rate of development of storms that do form (where there is not regional drying…)
high latitude temperature trends plus increased water vapor results in reduced vertical static stability, especially to moist convection
Would that last point help explain the poleward shift?
Higher tropopause allows deeper thermal anomalies to form (?) – would that increase anomaly pressure gradients?
But the poleward shift would presumably partly (?) counteract the rising tropopause since the tropopause slopes downward toward the poles.
Increased role of latent heating may increase cyclone-anticyclone assymetry (I would guess) – in particular, latent heating of moist convection reduces the effect of static stability, tending to allow shorter-horizontal wavelength development (When the greatest baroclinic instability is at shorter wavelengths, the wavelengths of greatest instability tend to strengthen faster), while the anticyclones would tend to grow larger horizontally (or not shrink as much as the cyclones) because they have mainly dry convection.
But the latent heating would tend to put energy directly into the mesoscale features…
IF the storm tracks shift poleward, they would experience a greater coriolis effect. That, plus a lower tropopause at higher latitudes, minus the increasing tropopause height, would decrease the wavelengths of greatest instability.
Greater coriolis effect could reduce the relative importance of the cyclone-anticyclone assymetry due to the centrifugal acceleration.
If the total wind shear through the troposphere increases (increased wind shear aloft, decreased near the surface… with variations from that pattern), that would increase the wavelength of greatest instability.
But the overall potential vorticity gradient is generally northward except at the surface because of beta (the variation of the coriolis effect over latitudes), so from an IPV perspective, the temperature gradient at the surface (which acts like a topographically-caused IPV gradient) is critical (?).
… So would the baroclinic instability decrease in most places, with those systems that do develop tending to strengthen faster and behave differently…?
The thermal anomalies cause the cyclones and anticylones to tend to seperate into two pressure bands. But radiation of Rossby waves could do the same thing… (?) Actually IPV rossby waves include temperature effects, I think, so is that really one and the same thing (?)…
(PS storm track activity actually transports westerly momentum downward to the surface from the jet stream, not so much by direct mass transport but by dynamic interaction across vertical distances – the upper air and the lower air push and pull each other – basically, because, if one imagines a situation where the winds are in geostrophic balance, the winds at one level actually depend on the mass over some vertical distance, and when there is some vertical wind shear, this can disrupt the geostrophic balances that had been established before…)
If the anticyclones are bigger, will that cause frontal zones of the same intensity (mesoscale temperature gradients) to occur by concentrating a reduced temperature gradient into a smaller area (?) – by the production of air masses that cover larger areas…(?)
Of course, all this could change the aligments of the winds with the major topographic variations of the Northern Hemisphere, thus tending to change the dominant quasi-stationary wave pattern. And if the jet stream shifts poleward, the wavelengths would have to shrink to fit the same zonal wavenumber.
Aside from static stability changes, the changing temperature gradient would cause isentropic surfaces to slope downward to low latitudes in the upper troposphere and lower stratosphere; without changes in the IPV distribution in pressure coordinates, this would increase the isentropic IPV gradient, which, depending on…. could increase the westerly phase speed of Rossby waves, and … if that happened less at higher latitudes, then would that tilt the waves so as to increase an equatorward group velocity that would pull wave energy out of the high latitudes, thus increasing the strength of the circumpolar vortex, which in winter would couple with the tropospheric circulation (I’m still learning about that – I took a couple months break from it but I’ll get back to it)…??????
Changing wind patterns could change horizontal wind shear. Horizontal wind shear can be self-reinforcing throuh wave-mean interactions (Rossby waves tilted by wind shear tend to transport momentum up-gradient. Rossby Waves tilted against the shear can grow by barotropic instability (analogous to Kelvin-Helmholtz instability in vertical shear, and eddy growth in the boundary layer, except that those small eddies can then lose kinetic energy to smaller eddies, “and so on to viscosity”)
I think I’ve read that the North Pacific storm track might have activity suppression because of too much vertical wind shear … Well, that wouldn’t be favorable to the smaller wavelength systems, I guess (but I have more to read on that).
I would imagine that too much condition variability along storm stracks would suppress strong storms (in the absence of explosive development) because the different conditions would favor different wavelengths (???)
A reduced temperature gradient would not favor the wind shear for severe thunderstorms (depending…), but apparently the summer wind shear is sufficient for severe weather. Would the ‘magnitude’ of the dryline increase with greater overall water vapor – dry air aloft impinging on the side of a thunderstorm being a cause of strong downdrafts and momentum transport favorable to tornadic development… but that’s getting O.T. now, sort of – but what does happen to MCCs in global warming, anyway?
PS I’m guessing that if the overall pole to equator temperature gradient decreases enough, the westerlies would still dominate the highest latitudes, with maybe a midlatitude high pressure belt. Even without actual storm track activity.
That’s because – with two hemispheric Hadley cells and nothing else, easterly winds everywhere at the surface would cause a built up of westerly momentum overall in the atmosphere. This would occur until a balance is reached; the westerly momentum would pull air out of high latitudes, creating a polar low pressure system that would weaken downward, but this would have to continue until the low reached the surface; the sinking air would, by momentum transport, keep the westerly winds near the surface supergeostrophic, so that they would have enough kinetic energy to get through the pressure maximum, before turning easterly and heading toward the equatorial low. Maybe…
“Actually IPV rossby waves include temperature effects, I think, so is that really one and the same thing (?)…”
Sorry, no. The advection of temperature anomalies is linked to the tendency of the low pressure system to build into the cold air, which is a distinct nonlinear effect (relative to linear baroclinic waves), whereas the radiation of Rossby waves from an isolated vortex involves weakening and drift of a nonlinear feature with the production of linear waves…
“Of course, all this could change the aligments of the winds with the major topographic variations of the Northern Hemisphere, thus tending to change the dominant quasi-stationary wave pattern. And if the jet stream shifts poleward, the wavelengths would have to shrink to fit the same zonal wavenumber.”
But beta (the meridional gradient of the coriolis parameter f) would also be reduced with a shift to higher latitudes.
What do you brains think about post #3?
I would think that somewhere in the weather prediction files, they have records of 700mb and 850mb pressures. So it should be possible to construct
700mb and 850mb (horizontal) pressure gradients, and look for long term trends in the data.
[Response: that is what the reanalyses do – and they don’t show much change, though they have their own problems. -gavin]
Of course how much the midlevel winds are advected downwards might not be a constant, that is clearly affected by the vertical temperature gradient. Also the near ground level friction could be affected by low level topographic changes (for example building heights, and or tree heights). Is it possible that this study is seeing a reforestation signal?
A bit off topic, but I sometimes get asked about the potential effect of using wind energy on the weather. A not insignificant number of people are concerned that we might mess up the weather by harvesting the winds. I suspect a feild of wind turbines would have an effect similar to increasing the topographic roughness. Does anyone have any qualitative studies the debunk (or not) these concerns? Thanks in advance.
Patrick McNulty #3, #14: no reason why it shouldn’t work… alternatively, the same has been considered with OTEC (Ocean Thermal Energy Conversion) plants, which convert the temperature difference between surface and deep tropical ocean to useful energy. The problem with all these ideas is getting the engineering and operating economy right — operating on the high seas is challenging. OTEC could be closer to realization on these, as there are a number of small installations already in operation.
That too should reduce the surface temperature of the ocean (around 27C) and thus rob tropical cyclones of the energy they feed on. But obviously only for very large deployments. I seem to remember somebody has even a patent in for this :-)
Thomas #15:
It’s all a matter of proportions. You are redirecting a natural energy stream within the climate system for gainful use by consumers. Eventually this energy is dissipated as heat.
You can calculate the amount of energy that can be harvested in this way, in watts over the globe (like you could also for solar, another energy form for which this worry sometimes comes up); and then, you can compare these watts with the watts that anomalous greenhouse gas concentrations are already redirecting all over the globe. If you do this exercise on the back of an envelope — or using bc, the Unix bench calculator, my favorite — you will see that even very large deployments are still falling a few orders of magnitude short.
The current greenhouse forcing is already causing observable climatic changes. These give an upper bound of sorts on the global changes expected from large-scale wind or solar deployments. Of course local changes could be larger.
Re: # 16. Martin,
You are correct and they can also be combined with OTEC technology where as OTEC has go down to the cool waters at depth and use it to condense its coolant back to liquid form to be pumped again or pump the cool water to the surface. The tunnels can do this already with no pumps and the amount of cool water that can be used with OTEC is ENORMOUSLY HUGE!So OTEC can evolve to a dual cycle system of generating electrical power one by tapping the Ke of the gulfstream and the other by tapping its heat.
“Whether the wind of change is truly blowing through this continent remains to be seen…”
Exactly what does your hypothesis predict will happen?
“# dreamin2222 Says:
12 June 2009 at 10:02 AM
“Whether the wind of change is truly blowing through this continent remains to be seen…”
Exactly what does your hypothesis predict will happen?”
I think this is just fluffery that is meant to make the speaker look as though they are thinking on a higher plane.
I.e. I don’t think it means anything, therefore there’s no hypothesis.
> no reason why
I would bet the Gulf Stream would regard a large slanted tube with fish screens and turbines as an obstruction and route around it, rather than push water uphill through it.
Google finds many mentions of this idea in many blogs over several years; I’d suggest answering the questions in at least one, like:
http://hypography.com/forums/environmental-studies/12992-underwater-suspension-tunnels-prevent-global-warming-4.html
Here is a 1/600 scale model of a tunnel I threw together rather quickly from PVC pipe bought at home dept. Any questions welcome?KEYHOLES $34
http://icons-pe.wunderground.com/data/wximagenew/c/cyclonebuster/124.jpg
reference 21
Hank,
It can’t because it is flowing towards a lower pressure some of it will but not all of it.
Thomas, we just discussed this a bit on Tamino’s site, Open Mind. See:
http://tamino.wordpress.com/2009/05/22/its-going-to-get-worse/#comment-31993
Martin’s response is germane, I think, but I’ll just add that I found one study which attempted to measure directly the velocity reduction in the “wake” of an offshore wind turbine. They measured a 37% reduction in velocity 3.5 rotor diameters directly downwind from the hub, decreasing to a 12% reduction 7.1 diameters out. (This accords pretty well with the numbers suggested by the Betz limit and turbine efficiency estimates.)
http://www.risoe.dk/vea/projects/endow/papers/folkerts.pdf
Back of the envelope calculations show that it’s a very tiny proportion of global wind KE that could possibly be affected–and forests and buildings already produce similar effects on much larger scales, though, as Martin says, without energy production.
Can we rule out whether the mischief makers at HAARP triggered these events?
3 interesting links where I talk about them often and what thay can do to regulate climate just by regulating SSTs if interested.
http://www.wunderground.com/blog/Vortex2/comment.html?entrynum=16
http://www.wunderground.com/blog/RickyRood/comment.html?entrynum=122
http://www.space.com/common/forums/viewtopic.php?f=26&t=18255
Re 21,23
For wind turbines, the theoretical maximum efficiency (As I understand it, of conversion of the kinetic energy in the ambi-ent flow through an area normal to the wind equal to that which the blades sweep through) is, as I recall, 16/27. I don’t know exactly how this is derived but would guess the compressibility of the air is not a factor (??) and so should apply to all such ambi-ent fluid flow.
The reason is of course that if the efficiency were 100 %, the fluid would come to a complete stop just behind the turbine, which would be an obstacle to further inflow of kinetic energy.
So what happens is that a difference in pressure builds up with higher pressure on the windward side, which will continue to drive air through the turbine, but also causes air to slow as it approaches the the turbine and causes some air to flow around the turbine.
The air that does flow through the turbine has to contract in the direction of the wind and expand sideways in order to slow down (lose energy) while maintaining the same mass flow rate; even more so if the fluid is compressible.
That last issue would also pertain to turbines that run off a manufactured flow – the inflow area has to be narrower than the outflow area, and the ratio (factoring in density changes) puts an upper limit on conversion efficiency, because the outflow has to have some kinetic energy in order to exit through an area of finite size. But for manufactured conditions, we can use a design with a very narrow inflow (nozzle) and wide outflow. Of course, the total efficiency will be higher than just the fractional decrease in kinetic energy between inflow and outflow because the pressure drop in between supplies additional energy (and that would apply to turbines placed in ambi-ent flow, too, but in that case, the source of the pressure difference is the ambi-ent kinetic energy)…
Ocean currents can also be approximately geostrophic, so slowing them would cause drift to lower pressure (at the surface, generally toward lower sea level, except for the effect of air pressure variations) (A lens of warm (or fresh) water will spread laterally on the surface until the coriolis acceleration balances the pressure gradient, at which point (aside from radiation of inertio-gravity waves), the surface of the lens will act as a high pressure center and the base of the lens will act as a low pressure center.) Water level/pressure variations can also result from pi-ling up by wind stress…
“so slowing them would cause drift to lower pressure ”
Now, maybe a significant removal of energy for human consumption would have little effect relative to the scales of the currents themselves, but in an extreme case, removal of energy from the Gulf Stream would, I would guess, cause warmer surface water to drift toward the northeastern coast of the U.S. (and Nova Scotia, etc.), which would also raise sea level along the coast. Sounds like double trouble, but maybe (?) the effects of using currents for energy would be dwarfed by global warming itself.
” the surface of the lens will act as a high pressure center and the base of the lens will act as a low pressure center.”
Actually, the low pressure would extend below the lens to arbitrary depth if the potential density is constant below the lens, but the reduction of pressure below the lens as it spreads would cause adiabatic cooling of the water below, which, if potential density increases with depth, would restrict the vertical penetration of the resulting pressure and current anomalies.
“Sounds like double trouble, but maybe (?) the effects of using currents for energy would be dwarfed by global warming itself.”
Yep! Your talking tens of trillions of dollars caused by global warming maybe even hundreds of trillions!
Patrick, you are correct–the Betz limit derivation is for an ideal case, independent of fluid characteristics or device geometry.
Derivation available in Wikipedia, under “Betz limit.”
Patrick 027, The real issue here is going to be drought and the poleward expansion of the Hadley Cell. The AP covered the story, i.e the Archer & Caldeira 2008 paper: Jet stream moving north, study finds
The relationship between the high-altitude jet stream and surface winds is complex, but it must be related to the locations of high pressure and low pressure rotating systems, which create surface winds and which are also influenced by the position of the jet stream. This phenomenon is not regional, but global, so GCMs are needed to analyze it, probably not regional models:
You can see it beginning, I think, if this last winter is any indication, as there were several periods when rain was blocked out by high pressure systems over Southern California – and note the Santa Ana enhancement as well, and the relation to the new wildfire regime. It should also be pointed out that those are minimal estimates:
This might point to shifting wind zones – but recall, most continental wind site locations are linked to geographical features more than anything else – i.e. mountain passes, etc:
From http://rredc.nrel.gov/wind/pubs/atlas/chp1.html
That’s a great source for overall information on wind, wind power tables, etc.
Actually to set the record straight. Neither Michael nor Gavin gave “long interviews.” If you check your own emails, both of you responded only by e-mail. Short ones at that. Here they are:
First from Gavin:
Hi Seth, a few comments. The authors are clearly very careful about noting the fragility of the trends over the different data sets and I think that is very sensible.
One thing that might be useful is the figure I attach which is what our model suggests should have been the wind speed trends over roughly this period (you can play around with different times etc. here:
http://data.giss.nasa.gov/modelE/transient/Rc_ij.1.11.html ).
What it shows is that the models don’t anticipate any large changes in wind over land. The places with relatively large expected trends are in the southern ocean (related, in our model at least, to the polar ozone hole), and a little in the tropics, probably related to changes in the Haldey circulation (though it’s a little difficult to say more without some real analysis). Over the US there is nothing expected.
Now that doesn’t imply that there is nothing in the data of course, but it does underline that this isn’t likely to be a metric that is useful for distinguishing model skill.
As for the implications for wind energy – this is all in the noise. [irrelevant text omitted]
Overall, this study to me is mostly suggestive and might promote further research – for instance, are different kinds of weather regimes are associated with the changes, or are any trends associated with
differences in the frequency of the different regimes themselves?
Gavin
Now from Mike:
[irrelevant text omitted] It’s an interesting paper. It demonstrates, rather conclusively in my mind, that average and peak wind speeds have decreased over the u.s. in recent decades.
If this trend is due to human-caused climate change (something the authors don’t discuss–this would require additional work using climate model- based fingerprint detection methods), this would spell out a rather ominous and unanticipated ‘surprise’ feedback in the climate change problem; namely, that the continued burning of fossil fuels is actually impairing our ability to meet our energy needs with available alternative sources of energy. Clearly, further work will need to be done to confirm whether or not the observed trends can be connected with human- caused climate changes, and to investigate the scale of the problem, e.g. what about Asia, Europe, South America, etc. Mike
—
That’s it. No phone interviews. Nothing extensive. This is the sum total of our conversation.
Seth Borenstein, Science Writer, The Associated Press
[Response: Seth–I agree that the wording “long interviews” was poor. We meant absolutely no slight against you whatsoever, and we took no issue with your article. We just wanted to point out that there was far more context and nuance behind the issue than can be communicated in a short article–hardly your fault. Again, apologies for any misinterpretation that might have resulted, as least from my perspective. -mike]
Additional maps on wind availability and developable resources in the U.S.:
http://rredc.nrel.gov/wind/pubs/atlas/maps.html
The average annual map shows widespread areas of developable availability in central Colorado and western Wyoming,Idaho, and western Montana,among other regions.
http://rredc.nrel.gov/wind/pubs/atlas/maps/chap2/2-01m.html
Reading through that, rredc link, there are some eye-opening paragraphs that put a lot of the historical data in question:
Issue #1: Data analysis, processing and extrapolation:
“The wind resource analysis is based on data (where available) collected at heights of 20 to 60 m (65 to 200 ft) above ground at exposed sites. However, in most areas only near-surface data, 3 to 15 m (10 to 50 ft) above ground, were available for the assessment. Vertical extrapolation to 10 and 50 m (33 and 164 ft) is based primarily on the 1/7 power law using data from exposed sites.”
“Data available from many locations with measurements from more than one level indicate that, in spite of anomalies caused by terrain complexities and nocturnal jets at some locations, the 1/7 power law is generally appropriate (Appendix D). The 1/7 power law conveniently provides wind power densities at 50 m (164 ft) that are twice those at 10 m (33 ft).”
Issue #2: historical data coverage
“The twelve regional wind energy resource atlases were based on data collected before 1979. Most of the data used in the assessments were collected at anemometer heights and locations that were not chosen for wind energy assessment purposes. In many areas estimated to have a high wind resource, the certainty rating of this estimate is low because few or no data were available for exposed locations. However, since the later 1970s, hundreds of new sites have been instrumented specifically for wind energy assessment purposes, and many of these have been located in areas thought to have high wind resource but where data were previously not available or were very limited.”
Question: were sites without long records excluded from the study?
Anyway on the global scale winds maybe stronger
Earth vibrations indicate increased storminess
Seismic signals produced by oceanic waves reveal greater cyclone activity
http://environmentalresearchweb.org/cws/article/research/39192
http://www.scienceonline.org/cgi/content/short/324/5930/1026
And for something completely different
Alfred Nobel wrote in his will “to those who conferred the greatest benefit on mankind.”
Climate research and modeling is physics & Geophysics is part of physics as astronomy.
Climate Change is the most pressing problem of mankind.
The conclusion
Next Physics Nobel Prize should go to climate Physics!
And from Copenhagen and PR view I hope it will be James Hansen
PS
It’s not against the research in basic physics and astronomy nor for reducing the funding for CERN or any Overwhelming Huge Any Thing nor for more Nobel prizes in those fields.
Seth, maybe your next article could cover the fact that atmospheric methane levels are now spiking upward, suggesting that we have crossed a point of no return, where methane from melting tundra and perhaps now seabed clathrates are being released at ever-increasing quantities, sending the whole system into a vicious feedback loop or death spiral.
Other cheery news it that we have just surpassed ’07 for the lowest ever ice coverage in the Arctic for this date.
Things are looking very bleak indeed.
Re #37 Wili Says
http://www.ijis.iarc.uaf.edu/seaice/extent/AMSRE_Sea_Ice_Extent.png
Looks to me like we’re around 2004 levels here.
Since no increase in deep ocean temperatures have been seen (As verified by ARGO network), why would ocean floor Methane Clathrate deposits be outgassing as greater rates?
Where are you taking your Methane levels from?
http://agage.eas.gatech.edu/images/Data_figures/gcmd_month/ch4_monS5.pdf
This data suggests to me that the bulk of the rise in atmospheric Methane took place leading up to the super-El-Nino of 1998. Interestingly, the Northern & Southern Hemisphere levels show large differences, not a well-mixed gas?
Things are looking like business as usual.
Since 1,020 “Underwater Suspension Tunnels” can generate 13 trillion joules of pure clean hydroelectrical power from the Ke in gulfstream every six seconds this should be more then plenty to reduce fossil fuel Co2 emissions for the whole United States. By reducing Co2 in this manner and leaving the tunnels in cooling phase the Arctic ice will recover to levels before the industrial revolution. This will prevent the calthrate gun hypothisis referenced in post 37. Computer modeling will verify this. Any universities here? I would like a university to model the tunnels. Any takers? I would be glad to assist.
> “Since 1,020 “Underwater Suspension Tunnels” can generate 13 trillion joules of pure clean hydroelectrical power from the Ke in gulfstream every six seconds this should be more then plenty to reduce fossil fuel Co2 emissions for the whole United States. By reducing Co2 in this manner and leaving the tunnels in cooling phase the Arctic ice will recover to levels before the industrial revolution. This will prevent the calthrate gun hypothisis referenced in post 37. Computer modeling will verify this.”
I don’t think computer modeling could “verfify” this rather drastic sort of geo engineering at all. Only a 1-to-1 scale, long term experiment could and nobody would want to take responsibility for the potential consequences, let alone pay the bill. Anyway – just don’t forget the “off” switch and a fallback plan. In general, replacing one energy source that has a significant climate impact with another one doesn’t strike me as being a good idea.
A semi-serious Q on the suspension tunnels: Wouldn’t turbine maintenance and grid interconnect be a massive concern/problem?
Patrick AKA Cyclonebuster wrote in 39:
bobberger wrote in 40:
Mr. Cyclonebuster first showed up here proposing his solution to our climate problems back on 11 June 2009, two days ago.
You can see it here:
Winds of change, Comment 3
11 June 2009 at 2:29 PM
https://www.realclimate.org/index.php?p=688#comment-126771
A the time he hadn’t shared with us the fact that he could prevent the calthrate gun. He has considerable ambition. I have yet to see that he has any credentials than I do — zip. Or scientific papers. But he has guaranteed that we can prevent the calthrate gun if we use his approach, so perhaps we shouldn’t be so picky. Particularly with his offer to model the tunnels — and maybe the climate system, too? I hope so since I am a little busy at the moment.
Re: 40
The tunnels can produce electrical power while in either phase of operation cooling or non-cooling.During non-cooling phase the gulfstream is diverted ( SHUNTED ) back through the tunnel opening at the surface via the closed shunt valve while flow is still established across the turbine. The much warmer surface waters now flow through the tunnels. Cooling phase is re-established by throttleing the shunt valve back open allowing the deeper cooler waters at depth at near 50 degrees flow back up the tunnel. A thermocouple located down stream of the tunnel exit will sends its signal to a temperature indicating transmitter (TIT). This will allow a set point to be established and will control how much the shunt valve is open to achieve a certain temperature setpoint determined by computer modeling.So as you can see the have the ability to regulate SSTs which in turn will regualte climate something we are doing now with greenhouse gasses but it is not controlable.What we have now is runaway global warming. What we need is regulated cooling. You decide which is worse.
Re Ike Solem –
Yes, so far as I know, water resource issues may be the single biggest concern (too much, too little, too fast, too irregular…).
But at least from a purely scientific perspective it is interesting to consider all the mechanisms potentially involved.
And changes in the quasi-stationary wave patterns would affect the longitudinal distributions of storm tracks.
Some other effects – maybe these would be subtle – but if cyclones moved more slowly (would that happen??), or if they are fewer in number or smaller in horizontal size, but stronger, with larger anticyclones in between, that could increase day-to-day, week-to-week water resource fluctuations…
And if the pattern of global warming projects partly onto NAM/SAM, might NAM/SAM internal variability patterns also change?
Re 43 –
One point of concern –
Redistribution of conditions over space and time across the globe could conceivably change the equilibrium global multi-annual average surface temperature without changing the global multi-annual average tropopause level radiative forcing. For example, if the warmest places and times could somehow be more positively correlated with clear skies and low humidity, if cloud area were somehow shifted from winter, high latitudes and nightime to summer low latitude mid-days by a change in atmospheric circulation patterns… etc. (How would this be accomplished intentionally, and would the regional climate changes that result be less severe than the reduced regional changes from reduced global average warming?)(OF course, such redistribution can be a feedback to global average changes – global warming may shift midlatitude cloud cover poleward, where the albedo has less radiative effect; greater solar heating of water vapor during the day might conceivably shift some convective activity to the night time(?)).
(PS I did some rough calculations on a spreadsheet and, with the approximation of the surface as a perfect blackbody, the variations in temperature raise the global annual average surface radiant emission so that it is the same as the emission from a uniform temperature blackbody that is roughly 1 deg C warmer than the actual global average.)
(But there could be some correlation between surface LW emissivity and surface temperature, but that’s probably not a big issue.)
BUT in general, if you move heat from the surface to depths to cool SSTs, the negative feedbacks that tend to pull climate toward equilibrium (PS positive feedbacks increase the shift of equilibrium in response to a given forcing, but unless climate sensitivity is infinite, negative feedbacks will dominate in the response to an unforced change – see
http://www.skepticalscience.com/argument.php?p=19&t=512&&a=18#3341
(and the comment immediately following that),
http://www.skepticalscience.com/argument.php?p=20&t=512&&a=18#3359
).
In other words, if you pump cold water to the surface, you will pull the climate away from radiative equilibrium; the net radiative heating rate of the surface+troposphere will increase. In net, this temporary surface cooling will speed up the heating of the deep ocean more than it would slow the heat gain of the upper ocean.
Maybe this could be justified (setting aside other concerns) as a way to buy time until clean energy and carbonate mineral production techniques are so affordable that we can start removing CO2 from the atmsophere, and/or to slow the initial rate of change to reduce adaptation costs and losses.
One big problem with marine power generating systems, is growth of marine organisms.
Any tunnel based system ould quickly have its performance degraded and also require either labour-intensive (Divers scrapping growth off) or potentially highly toxic (eg TBT) coatings.
In other words, if you pump cold water to the surface, you will pull the climate away from radiative equilibrium; the net radiative heating rate of the surface+troposphere will increase.
RE: 45 AND 46
45 “In net, this temporary surface cooling will speed up the heating of the deep ocean more than it would slow the heat gain of the upper ocean.”
Since the tunnels draw cooler water from the 1,000 foot depth you can not warm the waters below that since warm water rises and also because the sun can not penetrate the water that deep to warm it up!
46 “One big problem with marine power generating systems, is growth of marine organisms.
Any tunnel based system ould quickly have its performance degraded and also require either labour-intensive (Divers scrapping growth off) or potentially highly toxic (eg TBT) coatings.”
A small charge of voltage prevents this. Cathodic protection works fantastic in modern day power plant condenser systems. They will work fine out there in the gulfstream also.
Cathodic protection works in clean heat exchangers, but fouling of heat exchangers immersed in open water is a big problem today.
Might it work on living organisms in open water? Well, to my surprise, maybe, though this isn’t proven yet:
http://books.google.com/books?hl=en&lr=&id=olnPUdL6Rt0C&oi=fnd&pg=PA315&dq=cathodic+protection+heat+exchanger+fouling&ots=ygEbRsiY10&sig=6MTbbLEYorxE9n_Z7mhYvRacPTA#PPA305,M1
(which is cautionary about aspects of climate change involving biofilm formation, and worth a look for that)
The deep ocean water can warm, and has warmed:
http://www.nature.com/ngeo/journal/v1/n7/abs/ngeo217.html
Self-driving deep water fountains may require added salt.
Perhaps you’re thinking of this, an idea that goes back to the 1930s:
http://dx.doi.org/10.1016/j.dsr.2006.10.002
Wili Says:
12 June 2009 at 11:05 PM
Other cheery news it that we have just surpassed ‘07 for the lowest ever ice coverage in the Arctic for this date.
Things are looking very bleak indeed.
– Wili, there have been issues with the NSISDC data and the readings on this site are suspect. If you look at the IJIS site
http://www.ijis.iarc.uaf.edu/en/home/seaice_extent.htm
– it shows sea ice data as about the same extent as 2004 and higher than 2007. I think we really need to wait for the September minimum to make a real assessment.
Interesting, the SH sea ice extent is well above the average. Total cryosphere today is actually looking rather healthy. Cherry picked – of course !
#47 – I think I’ve seen you before.
Ahh yes, here we are, on Sciforums 2 years ago. Nice to see you’ve learnt some longer words.
http://www.sciforums.com/showthread.php?t=71613&highlight=cyclonebuster
Please read the link I have given before engaging with this person “Cyclonbuster”.