Newsgroups: lter.ced Path: LTERnet!news From: Bruce Hayden Subject: August 94 CED Message-ID: <1994Aug5.141419.21579@lternet.washington.edu> Sender: news@lternet.washington.edu Organization: Long Term Ecological Research Date: Fri, 5 Aug 1994 13:35:34 GMT ***************************************************************** ***************************************************************** *** *** *** *********** *********** ********** *** *** * * * * *** *** * * * * *** *** * * * * *** *** * ********* * * *** *** * * * * *** *** * * * * *** *** * * * * *** *** * * * * *** *** *********** *********** ********** *** *** *** ***************************************************************** ***************************************************************** Vol.3 No.8 ::::::::: August Issue :::::::::: August 3, 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 on ecosystems 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 at your 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@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-issues 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. CED is now a part of the World Wide Web. Web users can link to the following URL: http://atlantic.evsc.virginia.edu/julia/CED.html 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 bibliography on Climate/Ecosystem Dynamics that we pass on via E-mail. ***************************************************************** ***************************************************************** *** *** *** *** *** SOUND, SEX & PHYSICS *** *** *** *** *** ***************************************************************** ***************************************************************** The physics of sound propagation, attenuation, reflection and scattering is made complex by the development of a complete system of equations that use the following variables: the speed of sound, it angular velocity, its wave number, the horizontal wind speed in the direction of sound propagation, the specific heat at constant pressure and at constant volume, the universal gas constant, atmospheric temperature in degrees Kelvin, sound pressure amplitude, the del operator fo this or that, a unit impulse function and the x, y and z of a Cartesian coordinate system. That's complex and worthy of quiz questions! To circumvent this impediment to understanding and to avoid the difficulty of using equations in CED's e-mail system of fonts, I will "couch" this discussion in the lurid details animalistic vocal courting. To learn science quickly or to sell cars, the use of sex works better than equations. You might ask your spouse if this is a truism or a CED quirk. CED, now with a modicum of tradition in the use and abuse of humor in communication, is sure that sexual innuendo helps in the understanding of physics. ***************************************************************** ***************************************************************** *** *** *** *** *** LOXODANTA AFRICANA *** *** *** *** *** ***************************************************************** ***************************************************************** Consider two elephants with 30 Hz tooters. One toots from a fine hard pan and the other from a thick, forest humus surface. Price et al., 1998 tells us that the sound emitted from over the thick humus surface will be 6 dB lower in volume at 10 km than from the elephant on the hard surface. 6 dB is a factor of a 2-fold difference. At 15 Hz even the softest surface an almost perfect acoustic reflector. If you are a good, deep-voiced elephant your toots carry as far with the same sound energy over any kind of surface. Tooting for your mate on a uphill slope results in farther, louder sounds. Consider the dumb dumbo who toots for his mate from hill tops. The best arrangement is for a 10 Hz bull is to be downhill and the cow in the up hill position (+5 dB gained). The worst configuration is for the Bull to be at the base of the hill and cow to be in the next valley past the hill (-5 dB). An elephant with a falsetto 20 Hz has a +10 dB at hill top and a -10 dB in the next valley. The higher the frequency the more topography matters and preferential courting vs. topography should be considered. There is not much value in down-hill mate calling except in the movies where you find a fine silhouette against the horizon. Now if the wind is upon your back when you howl uphill the advantages are even greater. Lamancusa and Doroux, 1993 provide the skinny on topography and gender communication. ***************************************************************** ***************************************************************** *** *** *** *** *** SYLVAN COURTING *** *** *** *** *** ***************************************************************** ***************************************************************** We might ask if the trees get in the way of amorous vocalization. Vegetation will scatter sound but only if the size of the scattering elements of the sound (trees) is of the same magnitude or larger than the wavelength of the sound. So, consider a large 3 meter tree trunk in a contest with 30 Hz sound with a wavelength of about 15 meters. This LOXODANTA AFRICANA sound is not hindered at all by the forest! A 15 Hz amorous bellow has a wavelength of 20 meters and the forest is transparent to this sound like sunlight is to glass. Sylvan courting with a deep voice has little loss of efficiency. This topic is covered by Price et al. 1988. The greatest scattering and lest effective communication is around 250 Hz. Is it a good idea to issue forth your mating call through a narrow forest gap. This is sort of an ambush model. Carnard-Carauna et al. 1990 tell us that with 63 Hz cooings you gain about 3 dB in this kind of vocal courting. ***************************************************************** ***************************************************************** *** *** *** *** *** WHY ELEPHANTS DON'T HAVE HIGH SQUEAKY VOICES? *** *** *** *** *** ***************************************************************** ***************************************************************** To answer this question we need to look at the problems our species have with high frequency sound communication. At the upper ranges of the human voice sound is attenuated 40 dB per 100 meters. You got to stay close to your love if he, she or it has a high squeaky voice like this. If we had to use long distance vocalizations to find our mates we would have long ago selected against altos and sopranos and would have favored elephantine bellows with no gender gap when it came to frequency. An Elephant vocalization at 30 Hz has a sound intensity reduction of 1 dB per 10 km (at 20% relative humidity). At 5% relative humidity the reduction is 1 dB per km. So when the air gets real dry your calls just don't travel so far. ***************************************************************** ***************************************************************** *** *** *** *** *** WIND NOISE *** *** *** *** *** ***************************************************************** ***************************************************************** We all know that wind makes noise. Winds whistle and roar. Morgan and Raspet 1992 show that for a wind increase from 3 to 10 m per second, the wind noise increases 20 dB (nothing to sneeze at). Wind noise at 20 Hz is 10 dB greater than the noise at 200 Hz. So, the wind has a deep voice. Most of the turbulent kinetic energy in the atmosphere produce sounds below 40 Hz. So if it is windy and turbulent and you are an infrasound communicator in search of a mate, it would be best to wait till the winds die down. Even so the low frequency bellower has a real advantage over the high frequency whiner. Low frequency sound is attenuated less by the air than higher frequencies. ***************************************************************** ***************************************************************** *** *** *** *** *** DAY AND NIGHT CROONING *** *** *** *** *** ***************************************************************** ***************************************************************** During the day temperatures decline with elevation above the surface (so called lapse conditions). Under such conditions sounds are upward-refracting and so sound levels away from the origin decline at the surface as sound energy is lost to higher altitudes. With sunset cooling at the surface results in the building of a nocturnal inversion: cool at the surface and getting warmer as you go up. Sound is reflected downward. Canard-Carauna et al. 1990 found enhanced acoustic signal after sunset and through the night. So, wait for the sun to fall below the horizon and cold air to pool on the ground before vocal mate hunting. ***************************************************************** ***************************************************************** *** *** *** *** *** LONG DISTANCE SOUND *** *** *** *** *** ***************************************************************** ***************************************************************** To get sound to go a long way the recipe is low frequencies, great intensity, a hard surface, no wind, and a layered atmosphere. At Queen Victoria's funeral in 1901 great batteries of cannon were fired and the sound was heard in parts of Germany but skipped over the 500 kilometers of France and Belgium. A layered atmosphere with warm air aloft is ideal for such long-distance reflection of krieg-sounds. Sounds of a much lower frequency than elephants are capable of (0.001 to 0.1 Hz) can travel hemispheric distances and the are little attenuated by the atmosphere. Attenuation here means that scattering does not diffuse the sound. Sound intensity declines with the square of thedistance just like light and grviety. Because sonic booms, chemical and nuclear explosions produce lots of such infrasound, our arms-control agreements with the former Soviets included an international system of listening posts to monitor such sounds. It has also picked up sounds of unknown pedigree. The candidate sources of such ultra-low frequency sounds are severe storms, intense atmospheric shear of winds flowing across obstacles, and perhaps the winds on the sea surface. So the winds have their own voice. For those of us who have shunned high-dB hard rock, our ears are tuned to the frequency spectrum 16 to 20,000 Hz. Sounds below the range of human hearing we can term infrasound. Either some people have capabilities of hearing sounds <16 Hz or by means of bone conduction these pressure modulations are "felt" and are often the basis for predictions of storms. Marshall Islanders call these very "sounds" Lowa. The Bushmen of the Kalahari say these sounds are like a person humming to the windward. Such into-the-wind-humming would quickly and progressively be stripped of all its higher frequencies until they become sub-aural and only the keenest of eared would be privy to them. As storms generate such just sub-aural sounds, it is a reasonable hypothesis that the proud owner of such ears could predict the weather. He would have sort of cochlear-bunions! This probably explains the existence of bull-roarers. The most famous bull-roarer is that of the aborigines of Australia. They make a pointed oval airfoil to one end of which they attach a string. When whirled around their heads they make a helicopter-like low frequency sound which they call the "master of thunder." In West Africa, such infra sounds are called the voice of Oro. The frontal bone of the human skull can be used in similar fashion and is used in rainmaking work by the Apache, Navaho, Zuni, Ute and Kwakiutl people. Such oval pendants are found in Paleolithic occupation sites. We might consider a thunder hearing test to identify those among us with this capacity to hear the wind. ***************************************************************** ***************************************************************** *** *** *** *** *** HIDE AND SEEK *** *** *** *** *** ***************************************************************** ***************************************************************** As a youngster, a moonless night meant we could play hide and seek with adequate challenge. When an especially good hiding place was found it often resulted in exasperation on the part of the seeker. With sufficient seeker exasperation would come the request: "make a sound." I didn't know why at the time but you either made a deep gruff "over here" or a high pitched, squeaky "Hey!" The seeker would the do the calculus in his head, which humans can do before they take pre-calculus, and walk in the proper direction. If the hider is dumb enough to say "over here" or "Hey!" too many times the seeker could easily find you because humans can directionally localize sounds between 0.018 and 0.108 radians (1 to 6 degrees). See Lewis 1983 [Bioacoustics: A Comparative Approach. Adademic Press]. At the the time I didn't know it made a difference being a fathead or a pinhead in detecting sounds from the hiders. More on that later. ***************************************************************** ***************************************************************** *** *** *** *** *** DIRECTION FINDING *** *** *** *** *** ***************************************************************** ***************************************************************** Sound intensity declines with distance from its source (inverse square law with distance) and scattering). If the two ears on a head get the same intensity then the direction must be from dead ahead or behind. If the sound comes from the right or the left then the right or left ear gets a higher intensity respectively. The difference in intensity from ear to ear just isn't much. 10,000 Hz sound attenuates 70 dB per kilometer. A 1 cm span between the ears would have a gradient of 0.0007 dB and a 100 cm skull 0.07 dB. If the head casts a sound shadow on one of the ears. for example, the left ear is shaded when the sound is from the right and the intensity between the ears is greater. As a direction finding method it works less well at lower frequencies and less well in water than in air. The difficulty of distinguishing right in front from right in back or ahead 45 degrees right or behind 45 degrees left is reduced head moving, cocking or cupping your ear and by having ears that are directional "antennae" like LTER PIs (see Shaw 1974, in Handbook of Sensory Physiology). We humanoids angle our ears 30 degrees on the average. Now if there isn't much of a sound shadow then it is much more difficult to assess direction. This becomes a problem when the head circumference exceeds 1/4 of the wavelength of the sound (thank Lord Rayleigh for that one). The human head has a radius of 8.75 cm and a circumference of 0.55m. [See earlier CEDs for differences in head size among LTER scientists and NSF bureaucrats.] So we have a harder time direction finding with long wavelength (low frequency) sound than high frequency sound. So if your are in a tight game of hide and seek and the seeker wants to "make a sound" use the lowest voice possible and the seeker will remain confused. With a squeaky high voice at say 10,000 Hz the sound shadow of the human head is strong and directions finding is possible with some precision. It should be noted that fatheads have an advantage over pinheads as they can cast a greater sound shadow and do better at direction finding. Our friend the elephant with its 4.5m circumference head can use direction finding with 25 Hz sound. We would be lost trying to find our mates with such low frequency wooing. Another way of direction finding by sound takes advantage of the difference of arrival time for sound waves from one ear to the other. Sound from the right gets to the right ear before it gets to the left ear. Bats, for example, with 5 cm from ear-to-ear need to be able to sense an arrival time difference of only 0.15 microseconds. They do it. LTER scientists run about 20 cm ear-to-ear and need only detect a difference in arrival time of 0.6 micro seconds and our nervous system is easily up to this task. Fatheads here too have the advantage over pinheads. However, underwater with a faster velocity of sound means that the arrival time differences are much less and direction finding by scuba divers is difficult. Direction can also be determined based on the phase-shift (like Doplar shift for light) of the sound wave. Head size is important and so high frequency sounds (as long as they are not an exact multiple of the distance between the ears) work better than low frequency sounds. In Hide and Seek it is better to fool the Seeker with low frequency "I'm over here!" then a contralto "Hey!" Choose up sides now for the Coweeta Coordinating Committee meeting in October. It should be the Fat Head Seekers vs. the Pinhead Baritone Hiders! ***************************************************************** ***************************************************************** *** *** *** *** *** WHY WE NEED EARS AND FISH DON'T *** *** *** *** *** ***************************************************************** ***************************************************************** When sound waves come in contact with water, even at an angle perpendicular to the water surface, 99.9% of the sound intensity is reflected away and only 0.1% enters! Yelling at fish doesn't help much and it is hard to scare fish by talking. So sound into a watery medium like our flesh (read ears) is not very good and special things must be done to magnify the sound. We collect 1800 square mm of sound with our ears (LBJ did better.) and send it to our 70 square mm ear drum and then to the 3.2 square mm of the stapes attachment to the ear drum. So 1800/3.2 means a 563 fold improvement with yet another reduction in impedance of 30% due to the malleus, incus, stapes levers for a grand total of 730 fold improvement. So, even if only 0.1% of the sound gets into our flesh we magnify it adequately to do the job. Now fish are like the water and the sound well is transmitted in water with a rapid speed of sound and it blasts into the fish tissues will only small losses. Why stick ears on your body when your whole body is like a microphone? For a nice treatment on sound in water and air see M. W. Denny, Air and Water: the Biology and Physics of Life's Media. In fact, if you have a bookshelf with about 1.33 linear inches of space left this is the best book you can buy to fill it. It is published by Princeton University Press. If you don't have the bucks to buy a copy, be the first one in your university library and check it out for the semester. CED readers need to go back to the last issue of CED and credit Denny's outstanding book as I was lax and did not do my attribution job nearly well enough! ***************************************************************** ***************************************************************** *** *** *** *** *** GLOBAL WARMING UPDATE *** *** *** *** *** ***************************************************************** ***************************************************************** Global Warming Update This warming thing is like Waiting for Godot. Arrhenius in 1896 gave us a detailed view of what was in store for us and by the 1930s there were several true believers going from campus to campus rousing the rabble. There were calls for action during the 1940 but most people were more concerned about Hitler. By the 1950s and into the 1960s a global cooling spotted by climate data mavens and the numbers of those in line waiting for Godot dwindled. Theories to explain the cooling over the physically reasonable warming began to emerge. Reid Bryson at the University of Wisconsin put forward his "human volcano" theory which said that the some junk we dump into the air causes less sunlight to reach the ground and so temperatures fall. That caused a fire storm of pyrotechnic nay sayers. Like many issues in science it takes about 12 years for an idea to have its day and funding to run out. At the end of this period, the last major book on global cooling "The Genesis Strategy" hit the streets bringing a measure of talk show fame to its now global warming doting author. When the General Circulation Models were ready for their road show, extra CO2 was added because CO2 in the air retards the loss of earth light to space raising the internal energy of the planet and warming. It was found that the models made Earth warmer. Physics is wonderful. The Models showed that Arrenhius' 1896 pencil and paper calculations could be done with the same results by transistors. By the late 1986 Jim Hansen of NASA GISS fame was sure enough of his metaphysical construction (GISS) to go before congress and say that the warming would be visible by the early 1990s. Some cynics believed that Jim had 1993 (a third of the way through the decade) in mind. In the recently issued The Energy Report [7/8, p. 456 and 467-468] Hansen is quoted as saying that the "signs of global climate change will become evident by the year 2000." He said that our habit of dumping sulfates in the atmosphere has made Earth a cloudier, brighter planet and one in which at current levels cuts the greenhouse warming rate by half. It appears that the 1970s firestorm over Bryson's Human Volcano was a bit premature and perhaps even mean spirited. For those who do not know the modern vernacular mean spirited is worse than being just mean. Anyway, Hansen put in his model that sulfates make more and smaller cloud drops giving rise to more and brighter clouds and putting the physics of Beer's Law [The taller the glass the darker the brew, the less the light gets through.] into effect and fewer solar calories absorbed at the surface. The GISS Model when given less sunlight cools the planet and lessens warming. Because our air pollution control measures have put the breaks on sulfate emissions, Hansen is now sure that we should finally see the often called for warming by the year 2000. Earlier this year Jim relayed to the public that the warming we can't be sure we see now is that way because the heat is stored in the deep ocean, hiding in bottom water and will appear at some unspecified later date. Since the land heats up first and fastest and the land is where the thermometers are for the most part it is hard to see how the 2.2 Watts per meter squared of global warming got to the place where bottom water is formed so that it could be sucked down the bottom to hide for another funding cycle or so. Well the warming that we see in the time series of global or hemispheric temperatures now is 1) almost all at night and 2) happened in two steps one big one between 1910 and 1920 and a short duration one in the late 1970s. Since 1980 there is has been no change at all. So perhaps it is global warming after all but it is not a continuous function kind of warming but a step function! Well our models are made of continuous functions which are hard pressed to produce a staircase kind of output. Now those who study paleoclimatic records have longed pointed out the step function like behavior of climates in the long term would not find it surprising to see Earth behaving like a car on day one of lesson one of a 16 year old first time driver in Drivers ED usually taught by the football coach. ***************************************************************** ***************************************************************** *** *** *** *** *** CED JOINS THE WIDE WORLD WEB *** *** *** *** *** ***************************************************************** ***************************************************************** CED is now on the Wide World Web! The WWW, as it is known, can be accessed through graphical programs like Mosaic (Mac Mosaic, X-Mosaic, Mosaic for Windows) or non-graphical programs like Lynx (type from Unix prompt). Lynx allows you to download images and look at them later, if you have the right programs to view .GIFs (compressed pictures). Mosaic integrate images and the text. Set your web program to the following URL: (Under lynx type the letter g. It will then prompt you for a URL) (Under Mosaic, look under File for the load URL command. Mac users can use the command apple-u as well.) http://atlantic.evsc.virginia.edu/julia/CED.html. I will be putting up graphs and other images there that I can not send through e-mail. You can also access old issues though this web page.