Guest Post by Willis Eschenbach
It has been known for some time that the “Pacific Warm Pool”, the area just northeast of Australia, has a maximum temperature. It never gets much warmer than around 30 – 31°C. This has been borne out by the Argo floats. I discussed this in passing in “Jason and the Argo Notes“, and “Argo Notes Part 2“. I’d like to expand on this a bit. Let me be clear that I am by no means the originator of the claim that there is a thermostat regulating the maximum ocean temperature. See among many others the Central Equatorial Pacific Experiment. I am merely looking at the Argo data with this thermostat in mind.
First, Figure 1 shows the distribution of all of the ~ 700,000 surface temperature measurements taken by Argo floats to date.
Figure 1. A “histogram” shows how many data points fall in each of the 1°C intervals shown along the bottom axis. The maximum is in the interval 28°-29°C.
The number of temperature records peaks around 29°C, and drops quickly for temperatures above 30°C. This clearly establishes the existence of the mechanism limiting the oceanic temperatures.
What else can the Argo data tell us about this phenomenon? Quite a bit, as it turns out.
First, a look at the year by year evolution of the limit, and how it affects the temperatures at different latitudes.
Figure 2. Annual temperature variations measured by all northern hemisphere argo floats that exceeded 30°C. Temperature observations are colored by latitude. Click on image for full-sized graphic.
A couple points of interest. First, the cap clearly affects only the warm parts of the year. Close to the equator, that is most of the year. The further from the equator, the less of the annual cycle is affected.
Second, the majority of the breakthroughs through the ~30° ceiling that do occur are from areas further from the equator, and are short-lived. By and large, nobody exceeds the speed limit, especially those along the equator.
Figure 3 is a closeup of the years since 2005. I chose this starting point because prior to that the numbers are still changing due to limited coverage. To show how the mechanism is cropping the tops of the warmer parts of the year, I have added a Gaussian average (129 point width) in dark gray for each two-degree latitudinal band from 0°-2°N up to 10°-12°N.
Figure 3. Annual temperature variations measured by all northern hemisphere argo floats that exceeded 30°C. Dark lines have been added to highlight the average annual swings of the data by latitude band. Click on image for full-sized graphic.
As you can see, the warm parts of the yearly cycle have their high points cropped off flat, with the amount cropped increasing with increasing average temperatures.
Finally, here is the corresponding plot for the southern hemisphere:
Figure 4. Annual temperature variations measured by all southern hemisphere argo floats that exceeded 30°C. Click on image for full-sized graphic.
Note that there is less of the southern ocean that reaches 30°C, and it is restricted to areas closer to the equator.
Next, where are these areas that are affected by the temperature cap? I had always thought from the descriptions I’d read that the limitation on ocean temperature was only visible in the “Pacific Warm Pool” to the northeast of Australia. Figure 5 shows the areas which have at some point been over 30°C.
Figure 5. Locations in the ocean which are recorded at some time as having reached or exceeded 30°C.
Figure 5a. A commenter requested a Pacific-centered view of the data. We are nothing if not a full-service website.
Clearly this mechanism operates in a wider variety of oceans and seas than I had realized, not just in the Pacific Warm Pool.
Finally, here is another way to consider the effect of the temperature maximum. Here are the average annual temperature changes by latitude band. I have chosen to look at the northern hemisphere area from 160 to 180 East and from the Equator to 45°N (upper right of Figure 5, outlined in cyan), as it has areas that do and do not reach the ~ 30° maximum.
Figure 6. Average annual temperature swings by latitude band. Two years (the average year , shown twice) are shown for clarity.
Note that at say 40°N, we see the kind of peaked summer high temperatures that we would expect from a T^4 radiation loss plus a T^2 or more evaporative loss. It’s hard to get something warm, and when the heat is turned down it cools off fast. This is why the summer high temperature comes to a point, while the winter low is rounded.
But as the temperature starts to rise towards the ocean maximum, you can see how that sharp peak visible at 40°N starts first to round over, then to flatten out at the top. Curiously, the effect is visible even when the temperatures are well below the maximum ocean temperature.
Speculations on the mechanism
I want to highlight something very important that is often overlooked in discussions of this thermostatic mechanism. It is regulated by temperature, and not by forcing. It is insensitive to excess incoming radiation, whether from CO2 or from the sun. During the part of the year when the incoming radiation would be enough to increase the temperature over ~ 30°, the temperature simply stops rising at 30°. It is no longer a function of the forcing.
This is very important because of the oft-repeated AGW claim that surface temperature is a linear function of forcing, and that when forcing increases (say from CO2) the temperature also has to increase. The ocean proves that this is not true. There is a hard limit on ocean temperature that just doesn’t get exceeded no matter how much the sun shines.
As to the mechanism, to me that is a simple question of the crossing lines. As temperature rises, clouds and thunderstorms increase. This cuts down the incoming energy, as well as cooling the surface in a variety of ways. Next, this same process moves an increasing amount of excess energy polewards. In addition, as temperature rises, parasitic losses (latent and sensible energy transfers from the surface to the atmosphere) also go up.
So … as the amount of total radiation (solar + greenhouse) that is warming any location rises, more and more of the incoming solar radiation is reflected, there are more and more parasitic losses, more cold water and air move from aloft to the surface as cold wind and rain, and a greater and greater percentage of the incoming energy is simply exported out of the area. At some point, those curves have to cross. At some point, losses have to match gains.
When they do cross, all extra incoming energy above that point is simply transferred to the upper atmosphere and thence to the poles. About 30°C is where the curves cross, it is as hot as this particular natural system can get, given the physics of wind, water, and wave.
I make no overarching claims for this mechanism. It is just one more part of the many interlocking threshold-based thermostatic mechanisms that operate at all temporal and spatial scales, from minutes to millennia and kilometres to planet-wide. The mechanisms include things like the decadal oscillations (PDO, AMO, etc), the several-year Nino/Nina swings, the seasonally opposing effects of clouds (warming the winters and cooling the summers), and the hourly changes in clouds and thunderstorms.
All of these work together to maintain the earth within a fairly narrow temperature band, with a temperature drift on the order of ± 0.2% per century. It is the stability of the earth’s climate system which is impressive, not the slight rise over the last century. Until we understand the reasons for the amazing planetary temperature stability, we have no hope of understanding the slight variations in that stability.
My regards to you all,
w.
UPDATE (by Anthony):
Dr. Roger Pielke Sr. has some praise for this essay here:
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Steve Keohane says:
February 17, 2012 at 5:29 am
Steve, you are correct that because the opposite effect of evaporation is condensation, it also has to be a part of the equation. Generally, this occurs in the form of mist and fog. We get this here on the California coast from the air coming off the warmer offshore ocean, and then running across the cooler nearshore upwelling ocean.
And, as you point out, this must warm the local area, because when water condenses it gives off heat.
In most of the ocean, however, I haven’t observed this as a daily phenomenon. This may be because it is happening right directly at the surface, something akin to the formation of dew on the surface of the grass, and thus may not be all that visible. Or the conditions may not generally be favorable for condensation to occur.
I do note that dew usually forms on grass, metal, or other things that end up much cooler than the local ambient temperature … and I’m not sure that the ocean surface usually falls into that category.
Always more to learn …
w.
Have you ever noticed that dew never forms underneath awnings? On very calm mornings when dew forms all around it, my awning covers completely dry surfaces. I never thought too much about this but it must be back radiation from the awning preventing the surfaces from cooling enough to condense out any water vapor. It’s very noticeable on boats at anchor.
It doesn’t seem to matter how high the awning is either. I’ve seen this at 12 feet of separation and 2 feet. It would seem that the drenched top of the awning is a decent reflector.
Could it be that non-existent back radiation has bounced around my deck, chasing away the water vapor?
This might be a track too far or something but I’ve two questions that comes to mind when thinking about radiant energy…..
question 1:
Is it possible to increase the energy in a black body by a single source of radiation? It seems to me that, by definition, if the black body is a perfect absorber then it is also a perfect emitter and with no radiation difference it is impossible to increase the energy at all with a single source of radiation.
question 2:
If you claim the ocean can not absorb ‘cooler’ radiation, doesn’t this have to lead to the conclusion that the cool stuff has to be reflected? And, if the answer to that is yes, then don’t you also have to say that if the ocean can’t absorb at this ‘cooler’ frequency then it also can’t emit there? If I’m not missing something here then it should be simple to measure the long wave spectrum exiting the ocean and find holes in the emission spectrum to substantiate the claim.
“Tim, and all of your nitpicking about microns can’t change the fact that 20 microns below the surface of the ocean is ocean. Not air. Not land. Not handwaving. Ocean.”
Actually, it is neither ocean nor air.
The region involved in evaporation is a haze of interacting individual air and water molecules with air molecules and water molecules intermingling.
IR from the warm air above the surface doesn’t get past that haze and so doesn’t warm the ocean bulk or reduce the upward energy flow from the ocean bulk.
It it did get past that region and into the ocean then the thermal capacity of the ocean would ensure an unmeasurable effect for millennia with no apparent warming of either ocean or air.
“Could it be that non-existent back radiation has bounced around my deck, chasing away the water vapor?”
The warmth from your house (which includes the awning) keeps the temperature of the air below the awning above the dew point.
How about the awning on my pergola out in my yard? Same thing happens. It also happens underneath my picnic table. It happened above the deck of my sailboat sitting in very cold water in the Gulf of Maine. It happened on my sailboat sitting in the very warm water of Melbourne Florida too.
In fact, to my admittedly hazy memory, it has happened anywhere I witnessed an elevated surface covering anything in contact with the surface on a calm morning.
And, BTW, would that ‘warmth’ from my house be the radiation coming through my very cool siding?
Paul
I am thinking about your various comments and I think the points raised to be very interesting. I shall revert on them once I have thought a little more.
As regards the dew point, could this be a convection issue? It may be that there is a certain amount of trapping of warmer air below the awning (a semi ‘classical’ greenhouse effect arising from the reduction in convection).
As I say, I will come back on the photon point which is very interesting since if you are correct then this would potentially allay one of the problems I consider potentially arises if DWKWIR is absorbed in the micron layer of the ocean (the amount of energy theoretically being absorbed in the first 4 microns being such that there would be copious amounts of evaporation that we are not observing).
Richard: re convection under the awning.
I’m going hmmmmm here because when this happens it is always very calm morning air, i.e. very little convection. In fact I would go so far as to say very stable atmosphere and NO convection happening.
I’ve also given some thought to heating from adjacent ‘mass’ but another observation sort of kills that too…. On my sailboats at anchor I always put up an awning on the main boom that extended down to the life lines on either side of the boat. During the day with a nice sea breeze the foredeck, exposed to the sun, gets so hot you can’t walk on it in your bare feet. Under the awning the deck stays nice and cool. In the morning, the hot forward parts of the boat are awash in dew while the part under the awning is bone dry (as long as there are no leaks in the awning).
There’s no way my entire 40 foot boat gets warmed up from end to end at night by the hot foredeck. It’s far more likely that all the decks are radiating, with the foredeck more successful than the rest. The exposed decks cool down to the lowest temperature and they start out as the hottest.
Glad you enjoy my mutterings.
@ur momisugly Willis Eschenbach says:
February 16, 2012 at 8:01 pm
richard verney says:
February 16, 2012 at 4:23 pm
Willis
////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////
Willis
Once again a quite extraordinary response.
You state: “In response, you’ve gone all flannel-mouthed, and you say your statement was not an ad hominem. I know that, fool, I never said it was an ad hominem. Of course it’s not an ad-hom, I said it was a false statement. So your claim that it is not an ad hominem is just another sneaky way for you to seem to be apologizing, while doing nothing of the sort….”
When I read the post that caused you concern, I was doubtful that it could be reasonably construed as an ad hominem. However, there was a reason why I thought that you were concerned that it was an ad hominem. I personally consider that it was a good reason as I shall explain below:
Your post of February 14 to me reads and I quote by cutting and pasting to make sure that it is an accurate account of what you said:-
QUOTE
“Willis Eschenbach says February 14, 2012 at 11:40 am
richard verney says:
February 14, 2012 at 5:58 am
…..
Bull. Put up a cite showing that I was unable to put forward an explanation, or retract your ad hominem attack. As far as I know, that’s nonsense, and I’m tired of being attacked in roundabout ways. Either substantiate your bull or retract it, richard”
UNQUOTE
Now when I read the words “…your ad hominem attack” I apply the ordinary and accepted meaning to the words “ad hominem” and I understand that you are asserting that what I said was an ad hominem. I consider this interpretation of the words that you used is a reasonable interpretation of the words that you used, and I consider that an objective observer would also consider that that interpretation was a reasonable interpretation.
Of course, it may be that you write in code. But unfortunately, as far as I am aware, you have never detailed the code that you may be using and accordingly I did not take the expression “…your ad hominem attack” as meaning “… a false statement.” Forgive me for that but the expression “a false statement” was never used!
Unlike you, who claims to know what other people think, I am not a clairvoyant. It may be that you intended to say something different but not being a clairvoyant, I was unable to read your mind, and hence attribute some other interpretation to the expression that you used.
Certainly whatever be the correct interpretation of the expression “…your ad hominem attack”, I fail to understand how in your post of today, you can truthfully say “…I know that, fool, I never said it was an ad hominem. Of course it’s not an ad-hom, I said it was a false statement”
Clearly, as a matter of fact, you did assert that it was an ad hominem and as a matter of fact you did not say “it was a false statement”. That much is certainly clear when you read your post of February 14, 2012 at 11:40 am.
In the light of the above, I would appreciate receiving your full and frank explanation as to how you can truthfully say “…I know that, fool, I never said it was an ad hominem. Of course it’s not an ad-hom, I said it was a false statement”
.
Stephen Wilde says:
February 17, 2012 at 1:07 pm
Aw, jeez, more handwaving. OK, smart guy, if “20 microns below the surface of the ocean” is just some intermediate haze, an indistinguishable froth of “air molecules and water molecules intermingling” then what are they measuring the 20 microns FROM???
I say they are measuring from the SURFACE OF THE OCEAN, which is where the liquid starts. You say … what?
There is no mystical froth, no “air and water molecules intermingling” at 20 microns below the surface, that’s your fantasy. A liquid has a SURFACE, Stephen. Below that SURFACE there is water, with some amount of DISSOLVED gases. They are called dissolved, Stephen, because they are in the LIQUID. And 20 microns below the surface is LIQUID. Not handwaving froth, if your nonsense were true there would be no place from which to measure the 20 microns, would there?
You get your own theories. You don’t get your own facts. But I do love to see the contortions people go through to avoid facing the truth. You have some mythical froth instead of a surface, richard verney has sixteen feet of rain, and you never seem to notice the folks pointing and laughing.
w.
richard verney says:
February 17, 2012 at 5:04 pm
Richard, you are 100% correct, I had forgotten that I had incorrectly described your attack as an ad hominem. My bad, and my apologies.
Your statement was, of course, not an ad hominem of any kind, and if I had not been so enraged by your scurrilous attack I would not have written that incorrect statement. An “ad hominem” is an attack on a person in lieu of an attack on their ideas and claims.
Your attack was nothing of the sort. It was a false statement that I had never responded, and by implication could not respond, to your ludicrous claims.
I pointed out that I had responded, and immediately, to your claims. I linked to where I had done so.
That is what I’m still waiting for you to acknowledge, richard, and you still have not done so. I keep waiting for you to do that so we can get back to the science and you can explain how the global average rainfall is sixteen feet.
w.
Willis Eschenbach says:
February 17, 2012 at 11:59 am
“I do note that dew usually forms on grass, metal, or other things that end up much cooler than the local ambient temperature …”
====================
Dew (almost always) forms under a cloudless sky.
What does a layer of saturated air have to do with dew ?
Um, Willis.
That was a question not snark.
Paul
I think that there is a lot to learn from observation since this is showing us what is happening in the real world. It is good to see physical concepts in action.
Following making my post about convection, I saw Stephen’s comment about warmth from the building. I was not convinced that that was the explanation unless there is high heat loss. Your wider observational experience suggests that it is not a UHI issue associated with the adjoining building (which as you say would in any event almost certainly be radiation). That being the case, it appears to me that these canopies are either creating their own micro cliimatic conditions, or they are telling us something about radiation.
I myself was pondering about how dew settles differently on differnt colour cars, windscreen glass etc and whether there is something to learnt from that. Black cars get considrably warmer than white cars during the day but at night, in broad terms, you observe most dew on black cars, then on the glass areas of any colour car, then on white cars.
If your canopy is covered by dew, ie, a thin layer of water, does this film of water act as a block to the DWLWIR from the sky above, such that the ground below underneath the canopy is not receiving the benefit of the DWLWIR (or not all of it)? If so, how does this affect the radiation from the ground beneath and what affect does this have on air temperature beneath the canopy (asuming perfectly still air)? Will the film of water on the canopy not also be receiving the benefit of UWLWIR from the ground below? Potentially, there is a lot of interaction.
Quite fascinated by this whole IR vs water surface thing – an amazing process of temperature regulation …. this characteric of water, combined with its thermal capacity and freezing behavior makes it a unique climate regulator indeed.
But is all the IR energy lost as evaporation (note below although heat flux eventually reaches zero, currents are set up. (sorry for whole abstract … all seemed relevant)
Horizontal convection in water heated by infrared radiation and cooled by evaporation: scaling analysis and experimental results
A. K. Wåhlin, A. M. Johansson, E. Aas, G. Broström, J. E. H. Weber, J. Grue
Abstract
An experimental study of horizontal convection with a free surface has been conducted. Fresh water was heated from above by an infrared lamp placed at one end of a tank, and cooled by evaporation as the water moved away from the heat source. The heat radiated from the lamp was absorbed in a thin (less than 1 mm) layer next to the surface, and then advected and diffused away from the lamp region. Latent heat loss dominated the surface cooling processes and accounted for at least 80% of the energy loss.
The velocity and temperature fields were recorded with PIV technology, thermometers and an infrared camera. In similarity with previous horizontal convection experiments the measurements showed a closed circulation with a gradually cooling surface current moving away from the lamp. Below the surface current the water was stably stratified with a comparatively thick and slow return current. The thickness and speed, and hence the mass transport, of the surface- and the return current increased with distance from the lamp. The latent cooling at the free surface gives a heat flux which increases with the temperature difference between the surface water and the air above it. Hence the surface temperature relaxes towards an equilibrium value, for which the heat flux is zero.
The main new result is a scaling law, taking into account this relaxation boundary condition for the surface temperature. The new scaling includes a (relaxation) length scale for the surface temperature, equivalent to the distance the surface current travels before it has lost the heat that was gained underneath the lamp. The length scale increases with the forcing strength and the (molecular) thermal diffusivity but decreases with the strength of the relaxation. Numerical simulations of this problem for a shallow tank have also been performed. The velocity and temperature in the laboratory and numerical experiments agree with the scaling laws in the upper part of the tank, but not in the lower.
Willis writes “They are absorbed by the ocean, Tim, and all of your nitpicking about microns can’t change the fact that 20 microns below the surface of the ocean is ocean. Not air. Not land. Not handwaving. Ocean.”
But then goes on to blindly believe that somehow the backradiation ACTUALLY HEATS the ocean. No. There is a net loss of energy from the ocean from IR radiation.
We can argue about this all day. All I can see is that you have a distorted view about the process and that effects your understanding.
Paul Bahlin says:
February 17, 2012 at 12:33 pm
“…It would seem that the drenched top of the awning is a decent reflector…”
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Paul
I agree with this and this is another point that I have been trying to run with Willis but I think that Willis has not understood the point and that could well be because I have failed to adequately explain what I have been getting at. Although , I have been looking at this point from an absortion point of view, not from an exchange of photon at the molecular surface.
Water is essentially opaque to LWIR. According to accepted absorption figures, 20% of LWIR is absorbed within 1 micron, 60% within 4 microns and it is fully (for practical purposes) absorbed by 20 microns,
Water therefore acts as a LWIR blocker, much like a parasol blocks out incoming solar or sun cream blocks out harmful UV rays..
The point I have raised but probably not well explained is rough weather spray and wind swept spume/mist. I have suggested that often there is a layer of spray/mist/spume somewhat above the bulk ocean and that this layer (which is obviously more than 20 microns thick) shields the bulk ocean from the DWLWIR so that the DWLWIR does not interact/get absorbed with the bulk ocean.
As I say, I have been looking at this from an absorption point of view and have postulated that if there is all this DWLWIR and if this DWLWIR has energy capable of sensible work, it would all be fully absorbed in the first 20 microns of that spray/mist and there would be so much energy absorbed in the first 4 microns that there would be rapid evaporation. I have further postulated that this evaporation would take place before the spray/spume/mist is returned to the ocean. In this regard, the absorption of the DWLWIR is essentially a light speed process although the response time in energizing the water molecules in the first 4 microns to that necessary for some of them to break free and evaporate would be delayed a little but it would still be quicker than the mechanical processes of the effect of wind and waves returning the spray/mist/spume to the ocean.
Thus in this manner, the spray/mist/spume absorbs the DWLWIR (would carry much of it away in evaporation) and blocks it from entering the bulk ocean.
OK, I know that there are calm periods when there will be no spray/mist/spume but likewise over much of the world’s oceans there will be sufficiently adverse weather creating the right conditions.
I see this as a potential problem and one that needs an explanation. As I said, I had not been looking at the issue from a photon exchange perspective at the molecular level and I need to think a bit about that.
I would welcome your thoughts on how spray/mist/spume slightly divorced from the bulk ocean blocks DWLWIR from reaching the ocean below..
u.k.(us) says:
February 17, 2012 at 5:30 pm
Not sure what the question is there. Under clouds, the DLR keeps the surface from cooling too fast. As a result, the ground surface doesn’t become cold enough to condense the dew.
Does that answer the question? If not, ask again.
w.
TimTheToolMan says:
February 17, 2012 at 7:26 pm
Thanks for the reply. However, I don’t think it ACTUALLY HEATS the ocean, as you would know if you looked, Tim. I’ve been over this semantical BS many times, including in this thread. I think the ocean is warmer with GHGs than it would be without GHGs. And this is why I ask people to quote my words. Where did I say that DLR heats the ocean?
Finally, you say there is a “net loss of energy from the ocean from IR radiation” … and I would agree. I put the upwelling IR at about 390 W/m2 and the downwelling IR at about 320 W/m2, for a net loss of about 70 W/m2.
I’m just not sure what you think the connection is between that and the absorption of IR by the ocean.
w.
Willis writes “I’m just not sure what you think the connection is between that and the absorption of IR by the ocean.”
Your analogy was one of a white and a black rock and they’re just not even in the same ballpark. The ocean has very specific properties at its surface and you’re just not thinking them through.
Willis said:
“There is no mystical froth, no “air and water molecules intermingling” at 20 microns below the surface, that’s your fantasy.”
See here:
http://en.wikipedia.org/wiki/Knudsen_layer
“On molecular level, the state of matter can be hard to define. From kinetic theory, it can be derived that if liquid is in contact with vapour, there is a small layer where the phase is between liquid and vapour. This region, several mean free path lengths thick, is called the Knudsen layer.”
richard verney said:
” I saw Stephen’s comment about warmth from the building. I was not convinced that that was the explanation unless there is high heat loss”
It isn’t necessary for there to be a high heat loss.
Condensation on a surface forms when a surface becomes colder than the air above and reduces the temperature of the air in contact with it to below the dew point..
Anything that blocks upward radiation from surface to sky will limit the rate at which the surface can cool. Hence that one gets less dew even under a table out in the garden.
Under an awning attached to a house the major component would be the awning reducing the energy loss to the sky from the surface adjoining the house.That surface will gain most of its energy from conduction from the house.
So it is nothing to do with downward radiation from the sky. It is to do with the obstacle blocking upward radiation from the surface to the sky.
In so far as the obstacle itself might radiate downwards then that would be a function of the temperature of the underside of the obstacle which would itself be a function of the radiation reaching it from the surface below. The surface on the underside would not be affected by any radiation coming down from the sky and anyway there is none. The surface exposed to the sky cools rapidly hence the condensation on the upper surface of the awning or other obstacle.
markx said:
“An experimental study of horizontal convection with a free surface has been conducted. Fresh water was heated from above by an infrared lamp placed at one end of a tank, and cooled by evaporation as the water moved away from the heat source. The heat radiated from the lamp was absorbed in a thin (less than 1 mm) layer next to the surface, and then advected and diffused away from the lamp region. Latent heat loss dominated the surface cooling processes and accounted for at least 80% of the energy loss.”
Note that many infra red lamps emit infra red which is shorter wavelength than DWLWIR and so gets deeper but even so ‘at least’ 80% is lost.
The other 20% would be upward radiation, conduction and convection.
There is no evidence that any energy is left over to be transmitted down into the ocean but say 20% was thus available. It would take millennia to make a measurable difference if ever and if it went into the oceans it wouldn’t be available to warm the air.
The WÅHLIN et al article mentioned above is worth a look; below is a link to a pay-walled site – somehow I managed to download a full PDF from somewhere (in the background on my miserable, slow, Indonesian connection, but can’t find where I got it!) I’m sure you can find it with a good fast connection.
But.. it has very nice depth (cm) vs temperature (Celcius) charts at various distances from the IR source, and they show temperature rise down to 20 cm depth. There are also very nice colour maps of the temperature profiles.
The discussion section also covers implications of the findings on understanding ocean currents (which appears to be the purpose of the trial)
Now, this will all be more meaningful to many in here than it is to me, but using settings of 100, 200 and 300 watts, the calculated heat load on the surface was very high ranging from 1390 W/m2 to 6000 W/m2 …. But, to me, it does seem to show that if enough IR is applied to water surface, the water will be heated. However, they do not mention the actual wavelength emitted by the heat source.
http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0870.2009.00427.x/abstract
Horizontal convection in water heated by infrared radiation and cooled by evaporation: scaling analysis and experimental results
A. K. Wåhlin, A. M. Johansson, E. Aas, G. Broström, J. E. H. Weber, J. Grue
I hope the more learned here can expand on this.
If you’d like me to send a copy of the PDF xmarkwe at yahoo dot com
Stephen Wilde: February 17, 2012 at 10:13 pm
Says: “…Anything that blocks upward radiation from surface to sky will limit the rate at which the surface can cool. Hence that one gets less dew even under a table out in the garden…”
Does the above mean that the upward radiation must be (completely or largely) reflected back to the emitting surface? The surface does not ‘know’ its emitted energy was blocked and should have cooled the instant that energy was emitted…. (?)
So Stephen, now you say upward radiation is blocked by the awning. Fine. I agree and I assume by that you mean it is reflected by the awning and then absorbed by the surface below thus slowing the cooling that would otherwise occur. Since radiation is photon flux and photons have a characteristic frequency then I would further assume that the reflection process does not change the frequency, right?
Now here’s a question for you. If photons leave the ocean having a frequency that falls in the absorption band for water vapor, get absorbed by cold water vapor molecules in the stratosphere, leave the molecules (isotropically), sending a portion of photons back to the surface at the exact same frequency that they left at, won’t they be absorbed by the very surface they left?
Furthermore, how is that any different than the photons leaving a surface to be reflected by an awning?
Actually I would think that it makes no difference to the ocean whether those photons came from a gaseous thermalization, bouncing off a cloud, or hitting an awning orbiting in space. Agreed?
And as for this one,
“The surface on the underside would not be affected by any radiation coming down from the sky and anyway there is none”,
do you really want to go there?