Newsgroups: lter.ced Path: LTERnet!rnott From: "Bruce P. Hayden" Subject: CED 1.8 October Message-ID: <1992Sep28.123234.2949@lternet.washington.edu> Sender: rnott@lternet.washington.edu (Rudolf Nottrott ) Organization: Long Term Ecological Research Date: Mon, 28 Sep 1992 12:21:23 GMT ***************************************************************** ***************************************************************** *** *** *** *********** *********** ********** *** *** * * * * *** *** * * * * *** *** * * * * *** *** * ********* * * *** *** * * * * *** *** * * * * *** *** * * * * *** *** * * * * *** *** *********** *********** ********** *** *** *** ***************************************************************** ***************************************************************** Vol.1 No.8 :::::: file name:CED1.8 :::::: October 1, 1992 ***************************************************************** ***************************************************************** 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 get to 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@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 (monthly?). Back-releases 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 will keep a LTER wide bibliography on Climate/Ecosystem Dynamics that we pass on via E-mail. ***************************************************************** ***************************************************************** *** *** *** *** *** THICK SKIN DEPARTMENT *** *** *** *** *** ***************************************************************** ***************************************************************** CED 1.7 had some problems that can only be put at my cerebral doorstep. Not good. It resulted in conversations from Coweeta, Niwot, Luquillo, and Arctic Tundra, Kellogg, Andrews and network central. Not bad. For me it was an "Oh! Geeze!" followed by a "Hey, this is sort of fun." Most people stuck to the issues. Hobbie offered sage advice which I put in my wisdom file. Be it known to all that my skin is thick enough and welcome all commentary and discussion. Unless requested not to or unless the commentary and discussion is boring, I will forward the repartee on to all CED readers. Jerry can call it an experiment in real-time NETWORKING. Hobbie can call it proto-synthesis. Magnuson can call it a cross-site work. The rest of us may use the term banter. Thanks for your comments. ***************************************************************** ***************************************************************** *** *** *** *** *** COOL SOILS UNDER VEGETATION *** *** *** *** *** ***************************************************************** ***************************************************************** Last month's CED prompted one of our students to drop a paper on my desk. It is titled "The influence of vegetation on Soil Thermal Regime at the San Dimas Lysimeters" by H. K. Qashu and P. J. Zinke in the Soil Science Society Proceedings in 1964 pages 703-706. Q & Z looked at soil temperatures at .5, 1, 2, 3.5 and 5.5 feet below the surface under bare soil, grass, a pine forest and an oak forest. For the modeling types in the crowd, Q & Z offer theoretical equations derived from fourier heat equations parameterized for each vegetation type and depth. The study site is in Los Angeles County, California Soil temperatures in July ____________________________________________________________________ Site temperature (F) depth (ft) = 0.5 1.0 2.0 3.5 5.5 Bare soil 79.0 77.9 74.3 71.3 66.9 Grass 75.6 75.8 72.6 69.1 64.7 Pine forest 75.3 73.8 72.7 69.6 65.9 Oak forest 69.9 70.2 66.4 65.5 62.8 ____________________________________________________________________ So soil temperature is dependent on vegetation cover and changes in vegetation cover should change soil temperatures. Soils are coolest under the oak forest at all depths. Except in June, the warmest soil under the oak forest is at 1 foot depth with a cooler surface. Q & Z did not say why. Any ideas? Month of warmest soil Soil temperatures in July ____________________________________________________________________ Site temperature (F) depth (ft) = 0.5 1.0 2.0 3.5 5.5 Bare soil JULY AUG. AUG. AUG. SEPT Grass AUG. AUG. AUG. SEPT SEPT Pine forest AUG. AUG. AUG. SEPT SEPT Oak forest SEPT SEPT AUG. SEPT OCT. ____________________________________________________________________ The deeper you go the longer it takes (into the year) to experience the maximum in temperature. At some depth you go beyond the year. At some depth you are responsive to extra-annual heat gains and losses (see CED 1.7). Q & Z note that "The cooling effect of the oak is assumed to be a direct result of evapotranspiration, lack of air circulation, foliage albedo characteristics, and the soil moisture regime. This sounds like a we-really-don't-know answer. I would look to the role of the litter layer in heat conduction. A lower heat conductivity of oak litter (if it wasn't always damp) would moderate summer warming and winter cooling. In all months of the year the bare soil at all depths was warmer than all the vegetation covered plots. On a yearly average basis at 5.5 feet, the bare soil is 2.4 F warmer than the oak soil at the same depth. Clearly, the heat propagation to depths responsive to longer term heat gains and losses depends on what kind of vegetation cover is present. These kinds of numbers are really dependent on soil moisture; but, the data above are all from the same experimental site (same weather) and they are averages of 7 years of data. ***************************************************************** ***************************************************************** *** *** *** *** *** SAN JUAN, PUERTO RICO TEMPERATURE TRENDS *** *** *** *** *** ***************************************************************** ***************************************************************** The Cuba soil warming and vegetation change item in the last CED (CED 1.7) sent me searching for evidence of temperature changes in the region and perhaps closer to Luquillo. I found Claude E. Duchon's 1986 paper Temperature Trends at San Juan Puerto Rico [Bulletin Am. Meteor. Soc. 67(11):1370-1377. San Juan has apparently warmed up "monotonically" at every month and hour of the day Duchon checked for the time span 1956-1982. On a mean annual basis it turned out to be 2.1 C rise for the 27 years of record. Daily minimum temperatures have risen the most 3.0 C per 27 years. The first guess was that as San Juan got bigger, more metropolitan and sophisticated a urban heat island developed and became more pronounced. Unfortunately, the rate of warming was off the charts for trends due to urban warming relative to population growth. Duchon's theory is that the transition from palm tree agriculture to concrete moderinity accounts for the trend and he offers the notion that the airport local heat island is especially important. The airport has grown over time. Duchon presents other data that permit the alternative hypothesis that may be of some interest to our friends at Loquillo. They show that wind speeds have declined and the direction of the winds have also changed. In the 1950s, the morning winds came from the ESE (about 15 degrees south of east) and are now about 45 degrees south of east. Afternoon winds had come from 70 degrees east of north (from the offshore) now (1982) the come from 5 degrees north of east (by land parallel to the coast). In short the air progressively had to cross more land, i.e. more of the island, before it could reach San Juan. Since the islands are very much heated relative to the surrounding oceans [the island is a heat island], the air that comes over more land gets heated more. The biggest difference is in the morning and that is when the temperature trend is greatest 3 degrees in 27 years. Afternoon wind speeds have not changed much but morning winds have slowed down from 3.5 meters per second to about 2.5 meters per second. So in the morning it takes the air longer to get across the land area before it gets to San Juan. It crosses more land and crosses it slower. It can heat up more. At Loquillo there should have been similar wind direction and perhaps speed changes. The winds have, in recent years, come more out of the southeast and less out of the east. Why? We are not sure but I have research in progress that indicates changes in the shape of the subtropical anticyclone of the subtropcial North Atlantic has changed (1899-1990) and this would change wind direction. I will report on this when the work finishes up --- this fall. We have some fast graduate students. Loquillo will get all our long term data before it gets published. Soon. Have a look at Duchon's paper. ***************************************************************** ***************************************************************** *** *** *** *** *** VEGETATION AND WHICH WAY IS THE WIND BLOWING *** *** *** *** *** ***************************************************************** ***************************************************************** Our good friends at Harvard Forest are working on the 1938 hurricane, it's wind fields and the blow downs it produced. Emery Boose has built a nice model that brings ashore hurricanes and puts out wind fields (direction and speed). His focus right now is Harvard Forest, Luquillo and North Inlet LTERs. This is intersite stuff. Recently he put in topography to produce a high resolution, site specific wind fields and then compare them to the blow down records. The next step is to have a feedback from the vegetation to the wind field. He asked how I viewed the problem and so I will core dump here on the pages of CED. First, let me say that the sun builds the solenoids that accelerate the winds. So when sonny asks daddy, "Why do the winds blow?" you will have a cute answer. But, what are you going to do when he asks, "What stops the winds?" Just tell him the grass, flowers , shrubs and trees. On big islands like England wind speeds inland are about half what they are over smoother surface of the ocean (R. W. Gloyne. 1964. Sci. Hort. 17:7-19). The fury of the winds are dissipated mostly by the vegetation on the land and the waves at sea. That is about 2.3 watts per meter squared. That is the average for the Earth. That is about how much a 2XCO2 change will alter the earths radiation budget! The vegetation slows down the winds and makes them turn to the left in the northern hemisphere. Why left you say. Well friction slows down the wind. The Coriolis acceleration to the right is the Coriolis parameter times the velocity. So the coriolis acceleration gets less and is then smaller than the acceleration do to the pressure gradient and the wind turns left toward low pressure (down hill). Low pressure is to the left of the wind in our hemisphere! Well how many degree leftward does it turn. That is what Emery wants to put in his model to predict blow downs. Well it depends on how rough the vegetations surface is. A measure of such roughness is surface roughness (Zo). The maximum leftward turn is 90 degrees to the left. For this to happen the trees must have brought the wind to a stop! Friction this great can be found inside a forest. The winds inside the forest (light merry little breezes) tend to flow to low pressure. Find one of your colleagues who still smokes [you might have to go to the psychology department to find one or to central administration] take them out to your local forest and turn the smoking light on. Get him to puff away. Watch the smoke. Which way does it drift? Then look at the direction of movement of some low clouds. They should be about 90 to the smoke. These to low pressure winds in forests are called antitriptic winds. This is maxed out leftward deflection of the winds due to the total friction offered by the vegetation. If you looked at the leaves and twigs at the top of the canopy, you would see a wind direction about 45 degrees left of the free air flow above the trees. If you are testing out all these things right after Christmas you are likely to have lots of Christmas tree rain (plastic "tin" foil strips) or you can watch for your neighbor to throw out his tree for the trashmen. Neighbors rarely pick off all this scientific equipment before disposing. Take these little wind vanes and drape them (or tie them) to the branches of the trees from the top of the canopy (use one of Franklin's canopy insertion devices) branch by branch down through the canopy. Now you will be able to see the direction of air flow at all heights within the forest. You might even see (or photography) the eddies of air flow in the trees. How big are those eddies. Let me know. If you have to put the the cost of these little wind vanes into your LTER renewal budget you should plan on about $1.49 per box of 60 vanes. Well, how many degrees of leftward deflection should there be per unit of surface roughness. I have looked for the key regression equation for this and I can't find it. But here are some numbers I found and some that are stuck in between the found numbers based on published surface roughness numbers. Surface Degrees of leftward deflection __________________________________________ oceans 20* grass 20* city "canopy" smooth 30* orchard 30 Paris, France 45*# 20 m deciduous forest 50 30 m coniferous forest 60 Inside a forest 90 __________________________________________ * from Byers' General Meteorology, 1959 # from Landsberg (1970) other numbers are based on published surface roughnesses and Byers' data. Byers got his estimates by measuring the difference in angle between the winds and the isobars of the pressure field. Without friction, the winds should go parallel to the isobars. With friction, they cross the isobars to the left. Winds flow out of a high pressure system and into a low pressure system. I took a look at winter 1967 weather maps and looked for this angle at three LTER locations Coweeta (deciduous forest), Konza (grassland) and Sevilleta (desert). I picked days with straight isobars and no front or storm at the sites. I measured 12 angles for each site. Tossed out the highest and lowest values (This is Olympics diving methodology.) and found the average. LTER Site Vegetation leftward deflection of the winds ____________________________________________________________________ Coweeta# deciduous forest 52.2 degrees Sevilleta scrubby desert 43.5 degrees Konza grassland (shortish) 34.1 degrees ____________________________________________________________________ #Winds at Coweeta may also depart from the isobars due to channeling of the winds due to topography. So I found Sevilleta to be as rough as Paris, France. This is a unidirectional complement. Konza is like a smooth city. It just goes to show that vegetation is a better "baffle" for the wind that the unbending buildings of the city. Coweeta came out about as expected given the first table presented. Emery now needs to use his GIS and assign deflection angles to the pre-hurricane 1930 landscape at Petersham. He had forests and fields. So he should find places where the winds converged (here they must speed up) and other places where the winds diverge (here they must slow down). Landscape heterogeneity due to vegetation gives rise to velocity maxima here and minima there. ***************************************************************** ***************************************************************** *** *** *** A FANCIFUL VIEW ON *** *** HOW ROUGH MUST VEGETATION BE? *** *** *** *** *** ***************************************************************** ***************************************************************** The earth is a dissipative system (Paltridge [1979] "Climate and Thermodynamic Systems of Maximum Dissipation" Nature 279:630-631). About 2.3 watts per meter squared of the 230 watts per meter squared available each average day from the sun goes into making the wind blow (kinetic energy) and the rest goes into our internal energy, earth is a nice warm place. Eventually this 2.3 watts per meter squared gets converted to heat by means of friction. Most of this dissipation is into the vegetation on the land surface and into the oceans making waves. First the waves. The oceans, 70% of earth, we will say does 70% of the 2.3 watts per meter squared of dissipation. This raises the average wave height at sea to some value, its global climatic mean height. The vegetation covered land, 30% by area, dissipates 30% of the 2.3 watts per meter squared. A surface of "climatically average" surface roughness is needed to do all the dissipation work needed, i.e a vegetation height moasic that gives that global land mean surface roughness. Now what would happen if we had some strange sort of climate change that reduced the average planetary wind speed. Well, waves at sea might, on average, be a little less high or maybe be a little shorter in period (choppier). The other thing that could happen is to have less rough vegetation on the land surface. How do we do that. Well, we could have a greater abundance of shorter vegetation. We would need fewer forests except to print CED from your printer. However, slower winds usually (e.g. greenhouse studies) mean taller less stiff plants. Taller would increase surface roughness. Less stiff would lower surface roughness because the canopy would then be more wave-form and its steamlined form would be less rough. (Grace and Russell, 1977. J. Exp. Bot. 28:268-274. & Plant Response to Wind by J. Grace Academic Press 1977). With a less windy world we could have a more graceful world with lots of amber waves of grain. Now, what if people (men and women) went around with his trusty axe with a bent for hewing trees for the good of person-kind. The land would be less rough to the wind and the land area would do less of the total 2.3 watts per meter squared of work that just has to be done. Either the non-hewed land would have to get taller vegetation or stiffer vegetation or the oceans would have to do this work and build higher waves and put at risk your beach cottage and make sailing ships go faster. Lets see -- cut down the trees to get the sailing ships to go faster. That is what they did (not for that reason) in New England when they cut down the tall straight white pines for sailing ship masts. The more they cut down the faster the ships could go. Trade goods faster. Finance more ships that could go still faster. Now well before Emery's 1933 hurricane blew down the trees the New Englanders had left standing, most of New England had been carefully devegetated. The less rough surface permitted higher wind speeds close to the ground. In 1938, New England was ripe for Andrew like picking. Backyard avocados in Florida. Pines and Oaks in New England. Feedbacks are fun to run to doomsday scenarios. If you don't think that the surface roughness due to plants plays a global role, you need to read the stuff of Sud. [J. of Clim. 4:383-398, 1984; Monthly Weather Review 116:2388-2400, 1988; J. Appl. Metero. 27:1036-1054, 1988; J. of Clim. & Appl. Metero. 24:1015-1036, 1985 and Boundary-Layer Metero. 33:15-49, 1985] This last piece has been off the top of my head. True a flight of fancy but it does set one to thinking of what good the vegetation is anyway in a global sense. Just remember the sun speeds things up to the tune of 2.3 watts per meter squared and the vegetation must do its part in slowing things down the requisite 2.3 watts per meter squared. ***************************************************************** ***************************************************************** *** *** *** *** *** FLATUS GAS IN A GREENHOUSE WORLD *** *** *** *** *** ***************************************************************** ***************************************************************** Among the trace gas villains implicated in a warming world is methane. Are we Gaian liberators of this satanic gas? Not compared to the white-tail deer which is 240 times more flatulent than women (men as well) on a per kilogram of body weight basis. Nor to the warthog which is a modest 120 times more flatulent per kilogram of body weight. Flatulence is a matter of health, food, and choice. Yes, with some willpower, you can hold tight. Thirty to 50% of healthy people produce methane and release it as flatus gas. The rest of us hold it in, reabsorbing it into our bloodstream and letting our lungs do the release in a socially acceptable way. Make your own assessment of group membership. For the by-the-lungs crowd, exhaled methane production averages 1.5 ml/min. Humanity, as a collective, breathes a sigh of relief totalling 0.1 Tg/year. The back-door crowd run their engines with a flatus gas output in the range of 2 to 8 percent methane rich. Collectively, man produces 0.2 Tg/yr byh this method for a front-door, back-door total of 0.3 Tg/year. (One Tg/yr = 10 to the 12th power grams.) Global methane production is somewhere between 300 and 500 Tg/yr. We are not Gaian Villains driven by enteritic fermentation afterall. The global warming, at least methane's part, rests on the hooves of others. So you can breathe more easily. Data for this article comes from researchers who warned us of Nuclear Winter (now Nuclear Autumn) see Tellus (38B) 1986. Those interested in what microbes can really do should read J. E. Hobbie and J. M. Melillo in Current Perspectives in Microbial Ecology, ed. Kluge and Reddy, 1984. ----------------+--------------------------------+------------------------- Bruce P. Hayden | Dept. Environmental Sciences | bph@virginia.EDU (804) 924-0545 | Clark Hall, Univ. of Virginia | bph@virginia.BITNET (804) 924-7761 | Charlottesville, VA 22903 | (804) 982-2137(fax) ----------------+--------------------------------+-------------------------