Newsgroups: lter.ced Path: LTERnet!news From: "by way of bph@amazon.evsc.virginia.edu (Bruce Hayden)" Subject: CED 3.6/7 Part 1 Message-ID: <1994Jun23.135337.6998@lternet.washington.edu> Sender: news@lternet.washington.edu Organization: Long Term Ecological Research Date: Thu, 23 Jun 1994 13:24:43 GMT ***************************************************************** ***************************************************************** *** *** *** *********** *********** ********** *** *** * * * * *** *** * * * * *** *** * * * * *** *** * ********* * * *** *** * * * * *** *** * * * * *** *** * * * * *** *** * * * * *** *** *********** *********** ********** *** *** *** ***************************************************************** ***************************************************************** Vol.3 No.6/7 ::::::::: June/July Issue :::::::::: May 1, 1994 ***************************************************************** ***************************************************************** CED METADATA ---- CED is the Climate/Ecosystem Dynamics bulletin board of the LTER network. In CED, you will find exchanges of ideas, information, data,bibliographies,literature discussions, and a place to find experts within the LTER community. We are interested in both climate controls onecosystems and ecosystem controls on climate. As this is an inter-disciplinary activity,we hope to provide things that you might not come across in your work atyour LTER site. CED is a product of the LTER climate committee and contributions to CED for general e-mail release may be sent to either David Greenland of Andrews LTER [Greenlan@oregon.uoregon.edu] or to Bruce Hayden of the Virginia Coast Reserve LTER [bph@envsci.evsc.virginia.edu]. We expect that the scope of CED will evolve and reflect the interests of the contributors and users of this service. CED will be issued as the preparation work gets done (usually monthly). Back-issus of CED may be requested from Daniel Pommert [daniel@lternet.washington.edu] by the file name given in the masthead. Daniel can also add people to the CED mailing list. Feedback on CED from LTER scientists is welcome (non-$$$$ contributions also welcome.) For example, please forward citations of climate & ecosystem publications on your site. We are keeping a LTER wide bibliographyon Climate/Ecosystem Dynamics that we pass on via E-mail. ***************************************************************** ***************************************************************** *** *** *** *** *** THE MISSING TERRESTRIAL CRITTER *** *** *** *** *** ***************************************************************** ***************************************************************** Running, walking, sailing, gliding, jumping, hopping -- you name it, all of the ways "our kind" has invented to move around this world without motors have also been used by animals or plants except one. Hot air ballooning! I have not found a case where a critter uses heating to reduce its buoyance below that of air and loft-away. Is a hot-air-balloon design for a critter just impossible? Why is it that no organism has evolved to use this means of propulsion? The issue is thermal control of an organism's buoyancy and the metabolism that would be needed. Consider a 10 cm diameter, 1080 g/m^-3 density, gene-carrying, hot-air-balloon contender. The inside-the-balloon vs outside-the-balloon temperature difference is about 8.5 C. Ballooning flight becomes possible when the radius of the hot air bubble to the skin thickness gets to be around 100,000 to 1. This is like a 0.14 Watt light bulb. Not bad you say? Well the wall of the living balloon, which would have all the living mass, would have to generate these Watts, and would have a mass of 17 mg. For a 17 mg organism 0.14 Watts is a tall order. On a per kg of body weight basis this would amount to 8225 W kg^-1 to keep this living, hot-air balloon aloft. This is two orders of magnitude higher than any known organism can manage. ***************************************************************** ***************************************************************** *** *** *** *** *** HOT-WATER BALLOONING *** *** *** *** *** ***************************************************************** ***************************************************************** If an organism has density 1080 g/m^-3, and the ratio of its radius to its wall thickness is 10,000 to 1 then an inside/outside heat differential of 0.2 C is needed given an organism neutral buoyancy in water. The same fellow in the air would have to warm up about 108 C! But water unlike air is costly to heat up (4200 J kg^-1 C^-1). This is 10 times more costly than heating the air. And water is an excellent conductor and our water-living, gene-carrying, balloon-contender organism would loose heat faster than his impossible hot-air-ballooning competitor. It isn't an easy design. Even so there is one candidate water-living, gene-carrying, water-balloon-contender organism: the sperm whale. Most of us have wondered just why the sperm whale has such a big forehead! In his or her forehead there is an oil tank that holds 2.5 tons of whale oil. Over the range of temperatures in a whale's head (33 to 29 C) there is a 1% to 2% density change while the density change in water over the same temperature range is only 0.1%. So if the sperm whale desires to sink he cools down his head, he becomes more dense and down he goes. The whale can indeed control his head temperature [Clark, M. R. 1979 The head of the sperm whale. Scientific American 240(1):128-141]. Historically the sperm whale's forehead full of a couple of tons oil turned out to be like Bill Tell's son's apple. It was a harpoon attractor. ***************************************************************** ***************************************************************** *** *** *** *** *** CONSIDER A SPHERICAL CHURCH-GOER *** *** *** *** *** ***************************************************************** ***************************************************************** By the time I approached my present body size (skin surface area about 2.1 m^2), church in the warmer months was to me what global warming is to some. In my church, people didn't fan themselves. We just sat there and took it. Had I had a good biometeorology teacher at the time, I might have pressed to get one of the local car dealers to donate some folding, accordion-type fans to our good cause. The biometeorology of the pew sitters is interesting. Consider a spherical church-goer. Our spherical church-goer has, say, a radius of 0.5 m and a mass of 70 kg with a resting metabolic rate of 72.6 Watts/m^2 of body surface. [note: An average size male individual with 1.8 m^2 of skin surface area has an if-I-was-a-sphere radius of 0.38 m but we rounded-off our church goer to 0.5 m.] Anyway our church-goer with 1.8 m ^2 of skin would put out as much heat as a 130 Watt light bulb. You know how hot they get. Now think a pew-filled church of 130 Watters! Our individual in his pew, if he had no pores for sweating and could loose heat only by conduction, would have a body temperature in dead-still air 50 C above ambient. One would hope the minister conducted his services in a freezer at say -20 C. So break-out your folding fan that says Courtesy of Bill's Chevrolet and lets get into some forced convection. A 0.5 m/s fanned air velocity would mean that body temperature above ambient would be only 30 C. At 1 m/s it is 16 C. At 2 m/s 10 C. At 3 m/s 8 C. At 4 m/s 7 C. Now you can understand why your pew-mate leans over and says, "Slow down with that fan, it doesn't do much more good to go so fast and you look like a fool. A slow steady like a Gregorian chant-like speed is all it takes." Of course, give your church-goer back his sweating and it only takes a nice leisurely fanning to keep your body near ambient. All this requires a sermon that permits you to maintain a resting metabolic rate. If you get carried away with the message of the day and become active in the emotion of the moment, you will surely need to break into a good sweat and take advantage of the power of evaporative cooling. If we had to cool massive bulk only by conduction and could tolerate no more than 10 C above ambient, we would be limited to a spherical body radius of 0.0015 m. If we could rely on free convection, no wind machines please, then we could be a bit bigger, 0.0125 m. and with forced convection 0.1 m. If we permit ourselves to sweat a bit we can be much bigger still. If we lived in the ocean and could tolerate a +10 C body temperature above water temperature,we could be just a big as we wished to be. When air temperature gets higher than skin temperature (~32C) we gain heat by radiation from the air, conduction from the air, and both free and forced convection from the air. Only sweating will save your life. If you can sweat, then convection becomes your friend again. With all this talk about sweating we need to remind ourselves that we have two kinds of sweat glands: those for cooling and those associated with places that do not often see light and flood the skin with a bacterial-birthing-broth. It is this broth from the body vents that can ripen to an equilibrium in some 14 days! ***************************************************************** ***************************************************************** *** *** *** *** *** WHY ARE BEES FURRY? *** *** *** *** *** ***************************************************************** ***************************************************************** The furry thorax of the bumble bee must be good for something. For a critter to whom the cost of flight through the air is so great, the weight of the fur is indeed costly and a drag as well. Fur or pubescence in plants usually serves one of two functions: keeping the cold out and heat in or keeping water in. Bubble bees run their thorax muscles at about 30 C. It runs its furnace at as much as 200 W/kg. The mass of a bee is about 0.5 g. To take off on a cold morning the bee has to first warm up its thorax muscles to 30 C. It does this by shivering. For us a real good shiver can account for as much as 11% of our body heat. The bumble bee shivers as it sits there on its runway in preparation for takeoff. So it is important for the bee to keep warm during flight, especially when the air is cool. The fur coat comes in handy at that point. If the bee could get along without such a tubby body, it might be able to shed its fur coat. ***************************************************************** ***************************************************************** *** *** *** *** *** THE BEE AS A HOT AIR BALLOON *** *** *** *** *** ***************************************************************** ***************************************************************** It doesn't fly. The bumble bee keeps its thorax temperature 30 C when in flight. If air temperature was 0 C, a spherical 5 mm bee with all its metabolism in its skin,would need to have a very thin skin only 0.0008 mm to be even neutrally buoyant in the air. But the bee, cold blooded as it is, would have to stoke the metabolic fires to warm itself up some 30 C. With its designed metabolic capacity it can only elevate its temperature by about 20 C above ambient and so flight, much less ballooning flight, when temperatures fall below 10 C is dicy. ***************************************************************** ***************************************************************** *** *** *** *** *** KEEPING WARM IN THE WATER *** *** *** *** *** ***************************************************************** ***************************************************************** Some years back I made a number of raft trips down the Colorado River in the Grand Canyon for research purposes! The river water was around 55 F (bottom water temperature from the Glenn Canyon Reservoir). When you fall in your scalp hurts. It's cold. In not too long a time hypothermia sets in. Even if I were a 500-ton spherical Bruce Hayden with my usual metabolic rate I could only maintain a temperature 6.5 C above ambient water temperature. Well how does a 100 ton whale do it? Or a much smaller dolphins, seals and sea lions much less our friends the penguins at 40 C higher than ambient. Fur, feathers or blubber, that's what it takes. You have to 1) use Fick's law and reduce the temperature gradient between inside and outside to reduce conduction to a minimum, or 2) entrap poor conducting air around your body in your fur or plumage. ***************************************************************** ***************************************************************** *** *** *** *** *** THE ILLUSION OF SPEED *** *** *** *** *** ***************************************************************** ***************************************************************** Thunderstorms (N =120) have an average speed of 20 km/hr (12.4 mph). In general, they move at the average bulk velocity of the air within which they are imbedded. However, even on days with a bulk air velocity of 20 km/hr, thunderstorms give the appearance of faster movement. How so? In part this false speed is due to the "carnivorous" nature of the thunderstorm. Thunderstorms harvest great quantities of air from the surface layer. If there are many thunderstorms in the area they are in competition for the warm, moist latent energy rich surface air. Some win and other lose. Some grow and others die and evaporate and can be seen no more. Think of two thunderstorms (in still air) 20 km in diameter about 30 km between their edges. One consumes the energy of the other in say 20 minutes. It could well appear, depending on where you were viewing the system from, that the more carnivorous of the two moved that 30 km in just 20 minutes and thus had a horizontal speed of 120 km/hr. ***************************************************************** ***************************************************************** *** *** *** *** *** NEARSIGHTEDNESS *** *** *** *** *** ***************************************************************** ***************************************************************** Those of us who watch thunderstorms and their light-shows are struck by how many more we see on the horizon than directly overhead. Farmers over there seem to get more than their share of rainfall. A thunderstorm 50,000 feet high, a good boomer, can be seen as far away as 100 miles away. More thunderstorms are seen at a distance than up close. Much of our historical data on thunderstorm frequency is based on hearing thunder as we are somewhat "far-eared" We don't miss thunderstorms when we get them when they are up close. The visual thunderstorm counter is thus nearsighted sensor. Weather radar does not suffer such nearsightedness. Weather radar is our "Hubble-brand" corrective lenses. ***************************************************************** ***************************************************************** *** *** *** *** *** THE SOUND OF THUNDER (FAR-EARED-NESS) *** *** *** *** *** ***************************************************************** ***************************************************************** Because of the shortcomings of sound transmission we don't hear thunderstorms more than say 15 miles away. So our ears are thunderstorm sensors which sample at most a circle 30 km in diameter at the outside. Data like this comes from airports where trained ears record the presence of thunder each day and so we have the unit of measure thunderstorm-days. When you get one, you score a thunderstorm-day. _______________:____________:_ | : : | A MAP OF KANSAS | : : | | : 50 | Mean Annual | : : | Thunderstorm Days | 40 : | | : : | | : : | | : : | |___________:____________:______|