Guest Post by Willis Eschenbach
I stumbled across a lovely article about the Saharan silver ant over at phys.org. These ants have special hairs that reflect strongly in the visual and radiate strongly in the infrared. They show a photo of the ant hairs under a couple different amounts of magnification:
Figure 1. Photograph from the phys.org article on the Saharan silver ants and their hair.
The article says:
Saharan silver ants (Cataglyphis bombycina) forage in the Saharan Desert in the full midday sun when surface temperatures reach up to 70°C (158°F), and they must keep their body temperature below their critical thermal maximum of 53.6°C (128.48°F) most of the time. In their wide-ranging foraging journeys, the ants search for corpses of insects and other arthropods that have succumbed to the thermally harsh desert conditions, which they are able to endure more successfully. Being most active during the hottest moment of the day also allows these ants to avoid predatory desert lizards. Researchers have long wondered how these tiny insects (about 10 mm, or 3/8″ long) can survive under such thermally extreme and stressful conditions.
Using electron microscopy and ion beam milling, Yu’s group discovered that the ants are covered on the top and sides of their bodies with a coating of uniquely shaped hairs with triangular cross-sections that keep them cool in two ways. These hairs are highly reflective under the visible and near-infrared light, i.e., in the region of maximal solar radiation (the ants run at a speed of up to 0.7 meters per second and look like droplets of mercury on the desert surface). The hairs are also highly emissive in the mid-infrared portion of the electromagnetic spectrum, where they serve as an antireflection layer that enhances the ants’ ability to offload excess heat via thermal radiation, which is emitted from the hot body of the ants to the cold sky. This passive cooling effect works under the full sun whenever the insects are exposed to the clear sky.
They describe how the hairs “keep [the ants] cool in two ways”—by reflecting the visible light, and by strongly emitting in the thermal infrared.
Curiously, however, nowhere do they mention the importance of a third cooling method that I noticed as soon as I looked at their photograph—the shape of the hairs ensures that more energy is radiated upwards than is radiated downwards. I had never considered that such a thing might be possible. The silver ants have a layer of hairs above their skin which selectively radiate more thermal energy away from the skin than towards the skin. Amazing.
The hairs can do this because, as shown in the right half of Figure 1 and as described in their caption to Figure 1,
a) the hairs have a roughly triangular shape in cross-section and
b) the flat side of the triangular cross-section of the hairs is towards the skin and
c) the two upper sides of the hair are “corrugated”, increasing the surface area facing skywards.
The net result of all of these acting together is to minimize the surface area of the side of the hair facing the skin, and to maximize the surface area of the sides facing the sky. Energy will be radiated from the hair surfaces at some rate per square unit of surface area (e.g. watts/square metre). So the larger the proportion of the hairs’ surface area facing the sky, the greater the proportion of energy radiated skywards versus back towards the ant.
How large is the imbalance in radiation likely to be? Well, the triangular cross-section of the hairs in the picture are about equilateral (three sides the same length). This would mean twice the area pointing skywards as is pointing towards the ant’s skin.
However, there would still be some loss back to the ant’s skin from some portion of the radiation from the tilted upper surfaces of the hairs. Some of that sideways/downwards radiation would be absorbed by the adjacent hairs, however. And some of that back-radiation would be offset by the increased skyward-facing surface area resulting from the corrugation of the upper surfaces of the hairs.
So overall those lesser effects might cancel out in whole or in part, and thus it seems like the layer of ant hairs will emit something like up to twice as much radiation out towards the sky as it does towards the ant’s skin. As is often the case, nature shows the way … what an ingenious cooling method.
And what, you might ask, do Saharan silver ants have to do with climate science?
Well, looking at the cross-sections of the hairs making up the layer shown in the right half of Figure 1, I was reminded of the shape of a cross-section through a layer of tropical cumulus clouds. In particular, I realized that:
a) tropical cumulus clouds have a roughly triangular shape in cross-section and
b) the flat side of the roughly triangular cross-section of the clouds is towards the surface and
c) the upper sides of the clouds are “corrugated”, increasing the surface area facing skywards.
Just sayin’ … it’s something I wouldn’t have guessed was possible, that an absorptive atmospheric layer of clouds could radiate perhaps up to twice as much thermal radiation upwards as it radiates downwards.
I do so enjoy climate science, there are so many amazing things for me to learn about.
w.
PS: My usual request—if you disagree with someone, please quote their exact words that you disagree with. That way, we can all understand exactly what you object to.
Thanks Willis , my wife and I have often wondered about that , the flat bottom of T-storms or rising cumulus. Your observations are terrific and to us is way more important!! Why ? your thoughts are LOGICAL. Thanks you made our day! We are observers for the Can Gov and so always look for info, this is great stuff as is your tropical clouds theory you have proposed the last few weeks, as we say LOGICAL! And keep it up! You are very clear and understandable ( hopefully even to ” climate scientists” ).
“Curiously, however, nowhere do they mention the importance of a third cooling method that I noticed as soon as I looked at their photograph—the shape of the hairs ensures that more energy is radiated upwards than is radiated downwards. “
It actually isn’t true. As a matter of geometry, corrugation doesn’t help. The surface has more area to radiate from, but the view factor drops. The extra radiation impinges on surfaces rather than escaping to space.
It’s not clear to me that the high infrared emissivity is unusual. Many materials are pretty close to 1. It seems the main thing going for them is the SW reflectivity.
I wondered the same; however, these kind of questions are often trick questions from the mathematical point of view. It could be, and probably is, important for some reason of what shape the silvery hairs are. Exactly how, escapes me.
It’s a result of Lambert’s Cosine Law. If you are looking from outside, you see a component of the radiation proportional to the area of your view field that it occupies. Corrugations don’t change that, unless they increase the area subtended by the object. That’s why, if you look at a white hot body of uniform temperature, you don’t see any surface features.
The total radiative output is the sum of what such observers see. If they can’t see corrugations, then the radiation is the same with or without.
The ants could increase the radiation by having an outer shell of greater area, at the same temperature. But then they would be living in a “steel greenhouse”.
Nick, stop thinking professionally, please. Let us assume that we’re considering isosceles triangles, close enough to the image and simple. And let us formally note your unstated assumption that we’re dealing with a Lambertian surface, just to avoid confusion. Then certainly if I view such a single triangle from any angle around its circumference I will see a single value for radiative power. That is, watts per meter squared, observed will be the same everywhere.
But Willis’ point was not about changing the ratio of watts per meter squared, it was solely about doubling the meters squared that the surface radiates from.
I’ll grant you the possibility that you could, perhaps, carry your argument about a perfectly flat and perfectly corrugated sheet with respect to the total radiated flux. But even then we get nowhere if you don’t acknowledge that a silver ant isn’t perfectly flat and clouds are not perfectly corrugated.
Maybe like stealth aircraft surface angles.
Radiating fins to disperse excess heat on a spacecraft would have no meaning, if being long and thin did not increase the surface area from which to radiate. Just saying, more surface area, more energy at a surface, more radiation in all directions upward makes sense, so the corrugation works.
Nick Stokes June 22, 2015 at 4:43 am
“If you are looking from outside, you see a component of the radiation proportional to the area of your view field that it occupies. Corrugations don’t change that, unless they increase the area subtended by the object.”
But the important view is from inside the hair. From inside the radiation is more away from the ant than down toward the ant corrugation increases surface area _and_ has the same effect as a triangular surface. An outside single viewpoint is immaterial precisely because the radiation of heat from the ant is in multiple directions.
“Maybe like stealth aircraft surface angles.”
oh boy.
Let’s start with the F-117.
The F-117 has facets for one reason that most folks dont know. At the time the only codes for estimating reflections were codes developed from an obscure Russian paper. Using that code we could predict the reflection and backscatter from flat surfaces only. So to build a plane where we could make predictions that we could test in chambers and in scale feild tests the design had to be of flat plates. Manufacturing curces was also a bear.
The angles are designed to reflect returns away from an attacker coming at the front of the plane. The biggest airborne threat is a head on attacker so the lines and angles reflect returns away. There are still huge returns if you are looking at such a design from a differnt angle.
The break through in this approach happened at Northrop where we solved the problem for certain forms of curves ( like an Ogive ). Plus there were manufacturing breakthroughs in making curved surfaces.
What Nick says is correct.
“The biggest airborne threat is a head on attacker”
Sorry, but no. The biggest airborne threat is from behind. Compare the number of frontal hits with hits “up the tailpipe”.
Jquip wrote: “Nick, stop thinking professionally, please. Let us assume that we’re considering isosceles triangles, close enough to the image and simple. And let us formally note your unstated assumption that we’re dealing with a Lambertian surface, just to avoid confusion. Then certainly if I view such a single triangle from any angle around its circumference I will see a single value for radiative power. That is, watts per meter squared, observed will be the same everywhere. But Willis’ point was not about changing the ratio of watts per meter squared, it was solely about doubling the meters squared that the surface radiates from.”
Doubling the surface area doesn’t help at all, since one surface of the the hair points back towards the ant’s body, returning just as much radiation to the ant in that direction as it radiates away from the ant in the other direction. As you correctly point out, it doesn’t make any different whether one triangular side is facing the ant’s body or two sides and one vertex face the ants body, the flux in all directions will be the same.
Furthermore, unless these ants are – like Willis and Higley7 lost in outer space with radiating fins – any surface from which they emit LWR is a surface that will also absorb LWR (emissivity equals absorptivity). That includes DLR from the atmosphere and OLR from the surface of the desert.
This time, at least, Nicky is right and Willis wrong about the basic physics. The shape of the hair is irrelevant, as is whether a triangular hair has its vertex pointing at the sky, the ground, away from the body or towards the body. Evolution might have supplemented low absorptivity for SWR by arranged for a low LWR emissivity/absorptivity surfaces facing the hot ground and high emissivity/absorptivity surfaces facing the sky.
Frank June 22, 2015 at 11:05 pm
Thanks, Frank, but before you declare winners I’d be interested in your comments on my illustration of the question below …
Regards,
w.
As long as we’re going to focus on the ant itself — chitin is not Lambertian, full stop. So no, the physics aren’t wrong Just Because. But focusing on the construction of the ant itself is completely meaningless. Willis can be as barking mad and Not Even Wrong as he likes on the analogy that led to the point of this mental excursion. To wit:
The bulk of his post was simply color commentary laying out his through process that led to the hypothesis about the clouds themselves. With respect to which he stated the only meaningful thing that needs to be stated here:
Assuming we have one lambertian ‘cloud’ that is nicely isosceles and lonely, hanging by it’s little old self in the middle of a big sky — this is exactly and precisely what basic geometry requires. We needn’t even focus on Lambertian or non-Lambertian anything. His entire notion is predicated as:
Presuming that our lonesome cloud is opaque, Lambertian, and has it’s very own temperature it radiates at, then this is precisely the case. Right up until some smart bean wants to tell me how Lambert’s law permits an observer to observe the radiation emitting off the face not facing him this will remain the case. Of historically curious humor, Euclid’s 5th proposition — the one about the interior angles of an isosceles triangle — is fondly known as the Bridge of Asses.
Now with respect to a corrugation, where there is an end to end sheet of isosceles configuration, I won’t even dare say what will or won’t be the case with respect to total emitted flux when considering the entire surface area. I will state regardless that the observed flux will be equal in all observed angles as we would expect — subject to the constraint that we’re not dealing with the obvious temperature gradient that would occur in real materials from peak to trough versus the magic instantaneity of black bodies upon which Lambert’s math is based.
And while that latter is a very intersting notion — and horribly relevant to this site as it’s an issue of ‘back radiation’ — it is not something I feel inclined to don a gimp suit and grab a slide rule over.
@Steven Mosher
Head on from the perspective of the radar is exactly what I’m saying…From the suns perspective.
Some years ago Japanese researchers developed nano-etched surfaces that allow photons to diffract over adjacent sides rather than be absorbed. These hairs may, or may not, act in a similar fashion.
With this method emissivities of more than 2 have been claimed
This is correct, of course. But clouds are modeled as Lambertian. And while there are discrepancies from prediction they are considered to be a result of optical thickness of the clouds. This is my best understanding on the subject, but it is terribly old; so take it for what it’s worth.
Ahem … not exactly? Corrugation wouldn’t help if one were receiving radiation from a point or near point source. e.g. Corrugating solar cell surfaces probably wouldn’t make much difference in cell efficiency. My cocktail napkin here says it also won’t help if the corrugated elements are tightly packed. As you point out, with tight packing, the view factor will decrease by the same percentage as the “radiating surface area” increases. and will presumably exactly offset the gains from greater radiating surface. But if there is significant distance between the radiating elements, the “view factor” will increase while the radiating surface area stays constant, resulting in some gain in radiation efficiency. I doubt the effect is of much use for the ants which seem to have fairly densely packed, layered hair. But it might be significant for Willis’ cumulus clouds?
Nick, you’re looking at this exclusively as a radiation process. Actually, this kind of extended surface is a kind of “fin”, often employed in living creatures for cooling by enhancing the transferring internal heat to the air via radiation, convection and conduction:
https://en.wikipedia.org/wiki/Fin_%28extended_surface%29
For example, it has been hypothesized that Stegosaurus’ fin was used to transfer heat from its massive body.
The longer the fin the better is the heat transfer, but these ants would be rather clumsy sporting longer fins. So the extra length, in effect, is distributed along the axis provided additional surface area shielding as well. Would be interesting to apply calculus of variations, given conductivity and total heat vs mobility requirements to generate the the optimal geometry for this animal.
Why do you think that the ant hairs are Lambertian surfaces?#/media/File:SEM_image_of_a_Peacock_wing,_slant_view_4.JPG)
Me, I don’t know much physics. But, if the surfaces of the corrugations have highly asymmetric properties—highly emissive at right angles to the surface and progressively less emissive and more reflective as the obliqueness of the angle of incidence increases, then it seems to the corrugated surface would radiate more strongly (at the relevant frequency) than would a flat surface. Think of the limiting case–highly emissive normal to the surface, perfectly reflective at all other angles.
It almost has to be the case that the surface becomes more reflective as the angle of incidence becomes closer to the grazing angle.
10 million years of evolution can do a lot to optimize optical properties of organisms. I am pretty confident that butterfly wings are not Lambertian surfaces. This image
shows periodic structures in a bird’s wing that have dimensions of about 500 nm. Wouldn’t a few mm of such a wing have highly directional properties in the IR?
Bob
More triangles in rows. What a coinkidink!
Nick Stokes what you do not appreciate (and that applies to all who do not understand heat transfer) is that there is also convection and evaporation. Increased surface area increases heat loss by convection. The so-called radiator on a car or at the back of a fridge loses heat mainly by convection and not radiation. From a surface at about 50C natural convection and radiation are about equal. Forced convection ( when there is a wind can cause convection to be much greater than radiation. A wind also helps evaporation.
With more surface area you can pass heat to cooler air. But that is in short supply here. That is the difference from a car radiator. The ant’s problem is heat coming from the environment, not the heat it generates. Increasing exposure to the environment brings in more heat than it loses.
I would expect the air temp a meter above the sun-exposed surface to be a bit cooler than the surface. The ants, however, live in the air right next to the surface, where I would expect the air temp to be nearly the temp of the surface. I recall when I was young, I was fascinated by mirages of water puddles on the hot surface of the highway ahead, and how they would disappear as we drove closer.
If the triangular corrugated geometry of the hairs is irrelevant to radiative cooling and of little use in convective cooling, perhaps the reason for the shape is mainly structural? Or does a thick triangular hair conduct body heat to the radiating surface better than a thin flat one?
One other thought: During previous discussions with certain “doubters” of the so-called “greenhouse effect”, WUWT commenters have noted that a thermocouple immersed in a hot gas stream will register a lower temperature than the actual temp of the gas, due to radiative heat loss. The silver ant would seem to be a living analog of the thermocouple.
http://facstaff.cbu.edu/~jdavila/Heat%20Transfer%206th/Chapter%2001/sm1-086f.pdf
I think you are simply missing the fact there is one downward surface but two upward surfaces. It has nothing to do with what any particular viewer sees based on a viewer’s angle–that’s a red herring. It’s that there are more upwards facing viewing angles all with the same radiative flux than there are downwards facing viewing angles.
Nick Stokes wrote: “The surface has more area to radiate from, but the view factor drops.”
I am pretty sure Nick is correct. If Willis is right, the outer surface cross section looks like a triangle wave. Now draw an imaginary surface that just touches all the peaks of the triangles. It seems to me that it would violate the Second Law of Thermodynamics to have the upward radiative flux through the imaginary surface exceed the blackbody flux for at the temperature of the hairs.
But the shape may help with convective heat transfer, as suggested by johanus.
I can confirm what Nick is writing from my own experience in optics. Lambertian emitters work the same no matter what the surface roughness is. All that matters to the observer is how much surface area is in the projected direction of the observer.
Thanks Jeff
The point though is with this arrangement, the surface area remains fairly flat from any viewing angle above the ant, moving light away in the critical wavelengths.
From the vantage point of the ant the view angle is much smaller as the flat of the hair is at or near 90 degrees while the solar energy is reflected through about 240 degrees to miss the ant’s body from above. Really if the material has the proper molecular structure the reflectance can be optimized to be very wavelength specific as well. It might be fun to play with such a material.
Jeff, Mosh, Nick, I’ve provided an illustrated example below. Your comments are welcome.
As to the question of corrugation, if we are talking about black bodies you are all correct … but we’re not talking about blackbodies. We’re talking bodies with non-zero reflection.
What is at question is whether the radiation from an object is the same in all directions, or whether it is directional in nature. Let me give two examples to show what I mean.
Consider first a blackbody with a hemispherical recess in it. Let’s insert an omnidirectional LED every 5 mm or so all over the blackbody including the hemispherical recess to simulate the emission of thermal radiation …
Would such a setup make a directional light? Other things being equal, not in the slightest. As you all point out, in such a situation all that matters is how much surface area is in the projected cross-section in the direction of the observer.
Now, consider what happens if we replace the blackbody with a piece of silver, same hemispherical recess. Is there now a non-uniform, directional light? Of course, because the light inside the hemispherical recess is no longer absorbed as it was by the blackbody. Instead, it merely reflects around until it escapes. This makes the light directional, despite each of the LEDs being omnidirectional.
The same thing is true for thermal radiation provided that the reflectivity of the substance is non-zero. And as I showed below, for some substances the reflection of thermal radiation is definitely non-zero.
Anyhow, your comments on my drawing at the end of the thread would be appreciated.
w.
Corrugated surfaces do improve conduction to air, though. I expect the ants are using air for moderating their temperature as well as reflection and radiation.
Nick Stokes, June 22, 2015 at 1:15 am
Then why do we work so hard to increase the radiative surface area of heat sinks such as cool the cpu? Or your car’s radiator for that matter?
It seems to me your argument describes absorption from a point source, where radiation is proportional to the surface area with a near 180° view. The two are orthogonal.
“Then why do we work so hard to increase the radiative surface area of heat sinks such as cool the cpu?”<
Because we can. The air is the heat sink.
But for the ant, it's the problem, not the solution. The ant wants to stay cooler than the air. The only place cooler than the ant is the sky (away from the sun). So the strategy is to block as much incoming as possible (silver) and radiate upward.
But for that, surface corrugations don't make any difference..
The corrugation acts like an absorber which converts the absorbed radiation into a sort of jamming device on other frequencies of incoming EM.
So Nick, doesn’t that also give them more area to absorb downwelling or Back Radiation??
snicker…
[Willis Eschenbach ]
It is of my opinion that it is the “corrugation”, rather than the increased surface area, that permits more thermal energy to radiate away from the skin.
Thermal (heat) energy will migrate across a smooth surface …. but if it encounters a projection or “outward” bend in/on said surface …. it will more easily radiate (per se ‘jump off’) into the atmosphere (space).
OH my, my, …. in that no one responded to my above comment I began to wonder iffen they just thought it was utterly silly ….. and was just being nice by not criticizing it …… so I figured I had better do some “checking” just to see how silly it was.
And I found the following which confirms part of my statement about …. “thermal (heat) energy migrating across a smooth surface”, ….. to wit:
But that did nothing to support the 2nd part of my statement whereby I claimed that ….. “if it (migrating heat) encounters a projection or “outward” bend in/on said surface …. it will more easily radiate (per se ‘jump off’) into the atmosphere (space)” …… so I kept on a looking ….. and found the following
Which, …. on a macroscopic scale, ….. kinda, sorta supports and/or confirms the 2nd part of my statement.
Whenever I read something like this Shakespeare’s lines spoken by Hamlet always come to mind.
As true now as in the 16th Century
“(the ants run at a speed of up to 0.7 meters per second and look like droplets of mercury on the desert surface)”
These must surely be the fastest ants in the world – perhaps not surprising is they are treading on ground surfaces of up to 158 C. Rather reminiscent of the guest in a Canadian hotel in winter who complained about the peculiar noises from the steam pipes at night. Hotel manager sat up with guest next night in the dark, and they heard the peculiar sounds “pitter, patter, phef, phef, pitter, patter, phef, phef”, so switched on the lights, and saw a mouse running along the pipes and stopping every second or so to blow on his feet to cool them off. (Enough of that!)
But notice that humans are similarly biologically organized. Stand out in the sun and you will absorb energy in the ultra violet, visible and near infra-red bands, but will radiate in the far infra-red, at a black body temperature of 98.4 Fahrenheit.
BTW, have you ever seen an unconstrained droplet of mercury about 10 mm long and 1 mm wide?
Willis for President
I once saw footage of a scorpion , frozen in a block of ice, that was then put in a very hot oven. The ice melted away and the scorpion re-animated. Apart from having to do a dance to try to keep it’s feet off the hot surface, the scorpion survived undamaged. It’s truly amazing what extremes nature can cope with.
Another means of coping:
http://www.luerzersarchive.net/en/magazine/commercial-detail/25765.html
I try to be a rational person but I think the scorpion is actually proof of the existence of Satan rather than anything natural.
(If quoted or questioned I will claim that was just a joke!)
I disagree on several points
* you make the hypothesis that ants somehow manage to keep the hair in order, “the flat side of the triangular cross-section of the hairs is towards the skin”. Actually the 50 µm image, and even the 10 µm image when you look where hairs are not cut, seem to hint at the hypothesis that they DON’T. Hairs twist.
* hair seems (and for sure, should be) multi layered. This would make the bottom far from flat, and contradict your argument. It would, however, surely be a more efficient arrangement to prevent over-heating.
* about your clouds analogy : ant hairs are small enough to keep the same temperature on all three side, this is obviously NOT true for clouds.
I am still fascinated by these ants and still don’t understand how they can stay colder than the very air in which they move. I suspect that their speed is the key, because of some venturi effect that affect temperature of the air next to them. Pretty much like airplanes can experience freezing even in above 0°C air. I am not sure, though. Some computing required.
You’d probably have to include the effects of air viscosity too. At these sizes it may be dominant and kill any venturi effect with the result that the ant carries around its own little air bubble. Dunno though, some calculation required.
you’re right. I forgot “boundary layer”. Moreover, hair configuration has much effect on it.
Looks like a pretty hard problem.
That’s why it’s interesting.
Don’t mistake the ‘Aha!’ process of analogy for the necessity of the hypothesis it provoked. It’s color commentary. Likewise, it’s also the case that chitin — and assumptively the ‘hairs’ are made of such — is not Lambertian. Not a little not-such, but a whole lot.
But yes, the ‘twisting’ makes for an interesting statistical exercise for the masochistic.
paqyfelyc,
“don’t understand how they can stay colder than the very air in which they move.”
I don’t think that is the case. They stay cooler than the surface temperature, that is, the temperature of the sand they are running on.
Willis,
From having been flown in a sailplane once up to the base of a cloud on the top of a thermal – inside actually.
The base isn’t flat, it is dome shaped, so we were inside the cloud but in clear air.
I’ll leave it to you to decide if this shape concentrates something going down.
Dome pointing down, that is roughly the centre of the cloud at the lowest altitude, or dome upwards; that is roughly the centre of the base of the cloud is at the greatest altitude for the base?
@AnotherIan
> The base isn’t flat, it is dome shaped.
Hmm, the base of a cumulus cloud certainly is not perfectly flat, but tends to be less dome-shaped (i.e. flatter) than the top of the cloud.
http://www.birdmen.co.za/blog/wp-content/uploads/2011/12/dom-26-pv-4.jpg
I believe that is because there are two different mechanisms involved in the formation of these visible layers.
Cumulus clouds are manifestations of convection. Moist warm air rises and cooled by adiabatic lifting, causing the relative humidity to rise because cool air can hold less moisture than warmer air.
The height at which the relative humidity reaches 100% is exactly when the bottom of the cloud becomes visible. So the air just below the cloud tends to have the same absolute humidity as the bottom of the cloud, but is slightly warmer so remains invisible until it reaches a higher level. This level, called the lifting condensation level (LCL), is a function of the adiabatic lapse rate, which is determined mainly by thermodynamics (Boyle’s Law etc), which evidently is a more uniform process than convection itself.
But air at high altitudes is dryer than air at the surface. So the tops of cumulus clouds are manifestations of the vertical extent of convected moist air. The air above the cloud top is cooler than the bottom but much dryer and has less moisture to condense. This tends to be more random.
So the visible boundaries of clouds are due to the variation in relative humidity (bottom) and absolute humidity (top). The former has less variance and so looks flatter, the latter has higher variance so looks more fluffy.
Would the most latent heat be released at the bottom of the cloud, at the point where gas turns to liquid (albeit in a state of very small cloud-particles)?
Sometimes the edge of the top of the cloud is very crisp, clear, and expanding upwards at an impressive rate, and I have the sense that is where the gas is turning to liquid, so that is where the latent heat would be released.
However it does seem that, in the middle of the cloud, less latent head would be released.
(Someone else will have to do the math for me, for I did most of my cloud-studying during math classes.)
You’ve got it backwards. You can see, literally, where the condensation begins: at the bottom of the cloud. The boundary at the top is where moist rising air meets dry upper air, where condensation stops.
Yes, latent heat is released by this condensation, but that further warms the air, enhancing convection, so carrying this whole process even higher. Even more heat is released when raindrops freeze into hail. Until it hits the stratosphere which, by definition, is where all vertical convection stops. Then it spreads out horizontally, creating those peculiar anvil-shaped thunder heads.
Clouds are complex entities, mixtures of air, water and other aerosols, having both cooling and warming behavior. Clouds can absorb terrestrial radiation, in effect re-radiation part of that back to warm the Earth. But clouds also reflect a lot of sunlight back into space. And remember that all of that released latent heat represents energy expended at the surface by evaporation forming, in effect, a heat pump transferring surface energy to higher altitudes where it can more easily escape to space.
So overall a cooling effect.
Why aren’t we using this design to keep houses, cars etc cool in hot climates?
Material woven with similar shaped fibres could be used on rooftops etc to keep buildings cooler and reducing energy requirements. Hats, clothing etc could also benefit.
Cost.
Yes, cost, now, but give clever people a chance. I’m sure everyone is familiar with the creation of velcro.
I find the cross-fertilization of ideas by people of different disciplines discissing their fields to be extremely interesting. That seems to be how lithotripsy was developed. If would be inspiring if one of you WUWT readers had knowledge in material science and was thinking, wait, I know how to create that type surface cheaply. We would all be witnessing the birth of a new industry.
Well, heat-reflecting windows do this: they are double-pane windows with a heat-reflective metal-oxide layer on the outer layer, and a gas layer trapped between the two panes. As far as cost, the liners are available at Walmart, so not very expensive. It would be interesting to know if the hairs are hollow. Even if they cast a shadow they’d still need to be heat-reflectors.
Always interesting, Willis.
Ants can read as well. In times long gone by, someone wrote in capital letters, the word ADAPTATION into the sand of the dunes. The ants followed suit and they still live and prosper.
The hot priests of the carbon dioxide church cannot even read and they dont understand the meaning of that word….
Thanks, Willis, fascinating!
Unless I missed it I didn’t see a discussion of what is on the underside protecting the ant from the158°F surface temperature. In the spirit of adaptation, suggest a line of clothes based on this principle to protect us from CAGW. Always enjoy your Posts.
pyrotect
fire suits
Apparently, it’s just naked chiton on the (shaded) underside of the ant’s exoskeleton. If the setae (hairs) on the Sahara silver ants were being used primarily for radiative cooling, I’d think these hairs would be all over the ant’s body, including its ventre, or belly.
For a living creature, cooling off just means that the heat is moving away from the body.
I know this from hanging my legs and arms off the side of my bed during very hot weather like we are having now, so that a greater amount of skin is exposed to the air. It is for the same reason that ladies tie up their long hair in the summertime so that it is not hanging on the back of the neck.
Great stuff! No linear thinking in this exploration of nature. Another feature visible in the left hand photo (50microns view) is short ‘pins’ sticking out at right angles to the hairs or is this something in photography. Possibly these are spacers(?) or ties (?) that keep the hairs separated with distance from the body. The engineer in me sees some practical design applications here.
Very interesting stuff, but the scientists conducting this study likely will get no funding, for they forgot to splice some connection to Global Warming into the final paragraph.
They need to add that the range of these heat-loving, lizard-loathing ants “might have perhaps” expanded north 100 yards over the past three years.
3 other adaptations are at work:
This is a very ‘furry’ ant with an air gap between flat fur bottom and body. This would make for really calm air against body, providing excellent insulation.
Very straight triangular outer surfaces are like fins assisting with laminar flow at speed. Not sure what this means for conduction but laminar flow is way different than turbulent flow isn’t it?
Finally high speed means minimal ground contact; better pain management, and less conduction through their little feet. It might be that speed enables fewer feet touching.
Willis, do you have any high frame rate video so we can check this out?
“…hairs above their skin”
Willis, ants don’t have “skin.”
They have a chitin exoskeleton.
In regard to hear exchange the two function differently.
Just sayin.
Bert: Say “chitin exoskeleton” to the average “man-in-the-street” and you will get a look that says “WTF are you talkin’ about?” If you say “chitin exoskeleton” is “kinda-like” a skin, the look will say “Oh… OK”. Unless you happen to talk someone who has stayed awake in biology class or has had some invertebrate paleo. who will comprehend exactly what you are saying.
It’s true that the basic rigid element of insects and other arthropods is the exoskeleton which isn’t sheathed in a skin. But hairlike structures used for defense or sensing the environment seem to be found in a number of arthropods. Best known would be the defensive uricating hairs on spiders and caterpillars.
You should probably look up the definition of skin. All animals have a skin, made of various materials of course. Humans have a dermis, ants have an exoskeleton.
I would accept “cuticle”, or even “integument” as general terms for the outer covering of all animals, but I don’t believe “skin” includes the exoskeleton of arthropods.
Interesting that chitin is translucent, perhaps more so in these ants, so perhaps a prismatic or reflective effect is occurring to the visible light in those triangular hairs.
If anyone is aware of “skin” els ware applied to arthropods please give the reference.
Skin on an ant?
Think of it like- chicken lips.
Just like the skin of a jet.
Or the skin on a rice pudding
cool had never seen these before.
some google images of them
http://tinyurl.com/p6rr5x4
used tinyurl due to length of url it leads to a google search of silver ants and shows the images section
nothign nefarious
The hairs appear to be hollow. Open the image in a new window and expand a few times. What appears to be the tube wall is visible in the bottom portion of the triangle on several of the cut hairs. The tubes seem to have a very thin wall. Combined with the small size of perhaps 1 – 2 um. they must be very good insulators. Like a fireman in a burning building, the protective outer suit serves well for a while, but then it is time to get out and cool off.
Yes, the hairs definitely appear to be hollow. I suppose Buckminster Fuller would call them tetrahedrons – very elongated ones, at that – a geometrical form that fascinated Bucky.
Insects inhale O₂ and exhale CO₂ through spiracles or holes in the exoskeleton, thereby feeding cells directly through a system of tracheal tubes, which are then also used to route the exhaust CO₂ back out through the spiracles.
I wonder what gas is in the hairs?
I also wonder why the ant’s ventral surface (underside) is not hairy. Apparently the little creature’s hairs are there primarily as direct protection from the sun, rather than as an efficient way to shed heat, else we’d see the hairs all over the wee critter.
Were the ants sampled dead or alive as their condition at the time of the photos could change everything? How do you get a speedster ant to stand still for the microscopic camera?
Another inane thought, how many ants were sampled? Could be that a freak ant was looked at or that there are variations within the species or that some simply comb their hair differently. Do I need to note “humor” for the statisticians?
Wouldn’t that make it a Fabulous Furry Freak Ant?
“And some of that back radiation would be…..” What back radiation? Unless you mean radiation from the ant’s back! It is absorbed radiation of the hair, not back radiation as described in CO2 sending back heat to increase the energy in the Earths surface. If that was applicable to the ant, the heat leaving the ant would have to be absorbed by a hair in the sky and redirected back to the ant to boil it alive.
Instead the shape of the hair inhibits the speed of heat transfer from the sun, via the hair to the ant, by transferring a majority of what the hair absorbs to the air and not the ant.
The reflective parts should be self explanatory.
This got me thinking about the1974 movie “Phase IV”. A great underrated SF film. Check it out if you get a chance.
P.S. anybody got video links to these fast little critters?
And you got me thinking about Them!
Here is a nice one.
Cheers.
Thank you!
What amazes me is the reported maximum speed – 0.7 m/s – that’s about 10x faster than any ant I’ve ever seen!
But watching the video above, I totally believe it. Those little buggers can move.
“Largely due to the extreme high temperatures of their habitat, but also due to the threat of predators, the ants are active outside their nest for only about ten minutes per day.”
“They have longer legs than other ants. This keeps their body away from the hot sand,[2] and when traveling at full speed, they use only four of their six legs. This quadrupedal gait is achieved by raising the front pair of legs.[4]”
“A few scouts keep watch and alert the colony when the ant lizards take shelter in their burrows. Then the whole colony, hundreds of ants, leave to search for food. They must hurry before the temperature reaches 53 degrees Celsius (128 degrees Fahrenheit), a temperature capable of killing them.”
http://www.discovery.com/tv-shows/africa/videos/ants-in-silver-space-suits/
One incredible video, seems like something out of a Vin Diesel movie…
Noteworthy element of this video:
Only 3 or 4 guys doing all the work with the fly. ‘Hard to to tell with the editing, but in any case, when the surviving 3 ants arrive with fly, many more ants down in the shadows pull the dewinged fly into the chow hall. ‘Must be some kind of ant bureaucracy in that ant colony, where a few ants do most of the hard and dangerous work, and the rest of them do something else, like coddle eggs, or consort with the queen.
It’s also very interesting that these Silver ants do not have the magic hairs on the underside of their exoskeletons. I would expect the surface of the sand to be much warmer than the ant’s bodies, but apparently the greater danger is from above, and not from IR beaming from the burning sand at their feet.
Unavailable in Canada. Balzac.