Newsgroups: lter.ced Path: LTERnet!news From: "Bruce P. Hayden" Subject: CED Vol. 1.4 Message-ID: <1992Jun3.182543.955@lternet.washington.edu> Sender: news@lternet.washington.edu Organization: Long Term Ecological Research Date: Wed, 3 Jun 1992 18:16:48 GMT ***************************************************************** ***************************************************************** *** *** *** *********** *********** ********** *** *** * * * * *** *** * * * * *** *** * * * * *** *** * ********* * * *** *** * * * * *** *** * * * * *** *** * * * * *** *** * * * * *** *** *********** *********** ********** *** *** *** ***************************************************************** ***************************************************************** Vol.1 No.4 :::::: file name:CED1.4 :::::: June 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 Hayden by the file name given in the masthead. 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. ***************************************************************** ***************************************************************** *** *** *** *** *** BOREAL FOREST/TUNDRA TREELINE *** *** *** *** *** ***************************************************************** ***************************************************************** In 1966 Reid Bryson published his famous paper "Airmasses, Streamlines and the Boreal Forest" [Geograph. bull. 8(3):226-269]. The idea for the paper came from aircraft field studies of surface albedo in northern Canada. The central observation was that a cloud line that frequently positioned itself over the treeline. The central question was: Was this cloud line the result of frictional and thermodynamic (latent and sensible heat flux) differences between tundra and forest which produced upward motions and cloud development or was the treeline in equilibrium at the common or most common position of an atmospheric front? Wind data for many years was collected, resultant winds calculated and plotted on a map and streamlines resolved. Along the length of the treeline there was a confluence of air streamlines (a front) from different airmass source regions. The region to the north of the front was under the influence arctic air in all summer months. In contrast, the area to the south of the front had mild, maritime pacific air from the west in all summer months. The analysis was done for all of North America and mean frontal boundaries were geographically associated with biome ecotones. The conclusion was that the general circulation of the air over North America played a fundamental role in the location of this forest-tundra ecotone. It fits the paradigm: climate controls vegetation. Bryson thought that biome ecotones discovered from pollen core analyses could then be used to reconstruct paleoclimates [see World Survey of Climatology Vol. 11]. Bryson also showed that the northern treeline had been as much as 100 km north of its current position and as much as 150 km south during the Holocene. Now there is a new paper on the subject. Lafleur, Rouse and Carlson, 1992. (Internat. J. of Clim. 12:193-203) write on "Energy Balance Differences and Hydrologic Impacts Across the Northern Treeline." They find no differences on net radiation on either side of the treeline nor energy flux from ground storage. However the partitioning of available net radiation into latent and sensible heats are different. The tundra adds more latent heat to the air and the forest more sensible heat. These differences occur when water for evapotranspiration is not limiting. During dry periods the partitioning of energy is little different across the treeline. Under normal moisture conditions the forest has a higher Bowen Ratio than the tundra. So the lower part of troposphere warms (surface temperatures) more over the forest than over the tundra. Sensible heat generated by condensation (latent heat release) from tundra evaporated water would result in mid-troposphere heating. Lafleur and his co-workers suggest that changes in the treeline, which are documented, should result in changes in arctic hydrology as evaporation from the tundra is .2 mm/day greater than the forest. "The treeline represents an important climatological and hydrological discontinuity." It fits the paradigm: vegetation controls climate. In sum we have a bidirection climate/ecosystem arrow diagram for the tundra/forest ecotone. ***************************************************************** ***************************************************************** *** *** *** *** *** GLOBAL WARMING AND BRAINS *** *** *** *** *** ***************************************************************** ***************************************************************** Concern about carbon dioxide and global warming reached a zenith in the 1940s. The warming wasn't just around the corner back then, it was here-and-now to them. Popular Mechanics was more than a bit concerned and in April 1950 the interviewed Dr. Clarence A. Mills of the University of Cincinnati. According to Dr. Mills, the period of rising temperatures may result in smaller adults in the U.S., reversing a trend that has continued for decades. He went on to say that there would also be a retardation of mental keeness and the rate of development. A friend of mine interested in forecasting gave the following forecast in response to Dr. Mills: "Warmer and shorter, with a 90% chance of stupidity." Finds like this one from Popular Mechanics needs proper attribution. So a big CED thanks to finder Joe Lehnen of the Virginia Department of Forestry. ***************************************************************** ***************************************************************** *** *** *** *** *** DECOMPOSITION AND CLOUD MAKING *** *** *** *** *** ***************************************************************** ***************************************************************** Cloud gazers sometimes search for dragons, pigs and inlaw type relatives in the ?happenstance? shape of clouds. Others look for other details. Summer thunderstorm viewers know that cloud takes on a bubbling caldron form that looks like a cauliflower head. As the thunderstorm grows upward and the air and cloud drops cool, the drops change to ice crystals and the cloud edges are fleecy in appearance. The temperature at which this change occurs can be just below freezing or down to as low as -40!C at which point the supercooled cloud droplets may, all by themselves, form ice crystals. At warmer temperatures than -40 C, ice crystal formation may depend on decomposition of organic matter down on the ground! and for ice crystals to form at say between 0 C and -10 C lots of decomposition probably occurred somewhere below the air that now feeds the thunderstorm with ice nucleation particles!!! You guessed it. This is another of my little vegetation-controls-climate and in this case vegetation- controls-weather story as well. It is not enought to have cloud drop nucleating materials such as hydroscopic SO2 in the air. It won't help getting the ice crystals to form. Between 0 and -40 C there have to be ice nucleating materials present. Sea salt doesn't do the job until you get the cloud drops super cooled down to at least 35 C. Before we get to the juicy stuff on decomposition of organic matter we need to ask the question: What is the big deal about freezing anyway? Well, when the phase change between liquid water to solid water takes place about 80 calories per gram are released. The air becomes more buoyant, lifts more and the clouds can get smaller and more violent! Gee! Can you get tornados in air that is free of decomposition generated ice nuclei? I am just speculating for fun. Here is another answer to the what's-the-big-deal question. For water to fall out of the sky the drops have to get to be big enough. When they are small, like in a fog, they just hang around as a sort of suspension. Such suspension are clouds. How do you get all those little drops get bigger? Well, if you add a few drops that have ice nucleating stuff in them and the temperature gets low enough an ice crystal forms. Now we all know that the vapor pressure over water is greater than the vapor pressure over ice at temperatures below freezing! Right. So now the luck drops with the decomposition-generated ice nuclei grow larger by stealing water molecules from the liquid water drops! So decomposition increased the chances of a drop growing large enough to fall to earth and of course decomposition in the soil may be fostered by that drop from above. But that is positive feedbacking before we are ready for it. Proponents of this drop-growth-big-enough-to-fall theory categorically stated that ALL moderate-to-heavy precipitation was initiated in this fashion and that ONLY drizzle-type precipitation could fall from clouds which did not contain ice crystals. To get the Andrews LTER some bigger drops we need to put some barges of rotting organic matter out to sea (oceans don't put out many ice nuclei). There is a big east coast city with just the barges you need! Rotting vegetation controls climate! Here is YET another answer to the what's-the-big-deal question. You have to have "glaciation of cumulonimbus prior to the release of precipitation." Those cloud physicists talk funny don't they. Translation: you got have ice to get the drops big enough to get the rain. Without decomposition you would have to have clouds grow in height to around -40 C before you could get the rain out. People (cloud physicisits) have long wondered how you could get heavy rain and even thunderstorms at sea because there are so few ice nuclei in marine air that didn't just pass over vegetated continents. Well part of the storm is that thunderstorms at sea just have to get very tall before they do their thing. Over Coweta with lots of ice nuclei produced by the ecosystem the thunderstorms begin to rain shortly after temperatures fall just below 0 C! They may go on to get very tall 35,000 feet plus and have big drops in large quantities. Isn't there any other way to drops big enough to fall? Well yes. If you, by some process get drops of various sizes they will fall at different rates. The big-bully sized ones among them will bump into small ones as they fall and grow in size. By the ice crystal growth method a drop could grow from 20 microns to 200 microns in 5 to 10 minutes and by the bully-boy method such a growth would take on the order of 100 minutes. Both processes work in the real air. And -- the ice crystals if present are bully-boy drop makers par-excellence. If ice crystals are present they are in charge! Collision capture becomes more important as the drops get very big. I hope this isn't too much background to show you how soil microbes via their decomposition of vegetation controls important physics of the atmosphere. So I will move along on this now getting-to-be-long discourse. F. H. Ludlam of Imperial College and the British Met Office called drops with ice nuclei "infected droplets." Nice seeing that organic origin of the infecting stuff. Air from Prague (assumed to be loaded with decomposition origin ice nuclei) were largely materials that initiated freezing between -5 and -15 C. Nuclei that did the job at much lower temperatures were 2 to 4 orders of magnitude less abundant. So the we are especially interested in nuclei which do the job at these relatively high temperatures. Breakages of ice crystals in the air in the thunderstorm results in separation of + and - electrical charges and thus the prospect of thunder and lightening. Some think that without ice crystal growth it is hard to get the crash-bang part of thunderstorms we all love so much. So decomposition fosters ice which fosters electrical charges separation which fosters electrical discharges which set forest fires which ... Isn't this fun. Now to decomposition. I got onto this topic on reading R. C. Schnell (a you- should-read-all-his-papers type of guy) and G. Vali paper in Nature [Vol. 236:163-165] titled Atmospheric Ice Nuclei from Decomposing Vegetation. It is must reading. Their Figure 1 will get us started. Y-AXIS IS FREEZING NUCLEI ACTIVE AT -10 C IN POWERS OF 10 3 | X | | X | X X | 2 | X X | X | | | 1 | | | | | 0 | X | | | | X -1 +|---|---|---|---|---|---|---|---|---|---|---|---|--- 0.1 1 10 100 % ORGANIC CONTENT OF THE SOIL CED Graph note: 0 on the Y-axis is 10 to the 0 power and 2 on the same axis is 10 to the 2nd power. Schnell and Vali harvested material for their lab work from solution of soils of different soil organic contents. All of us don't-need-to-be-rocket scientists can see that ice nuclei are more abundant form soils rich in organic matter. The deeper in the soil profile the sample was taken the less the ice nuclei present. Since the soil organic matter can be traced to the vegetation above, Schnell and Vali looked at it. Y-AXIS IS ACTIVE NUCLEI/g DRY MATTER IN POWERS OF 10 9 | 4 | 4 | 4 LEGEND | ++++++++++++++++++++++++++ | 4 + 4 = poplar mulch + 8 | 3 + + | 3 + + | 4 + 3 = black loam + | 3 + + | 3 4 + + 7 | + 2 = sage litter + | 2 3 4 + + | 2 + + | 4 + 1 = green poplar leaf + | 2 3 ++++++++++++++++++++++++++ 6 | 3 4 | | 2 3 | | 2 3 4 5 | | 3 | 2 3 | 1 2 3 | 1 2 4 | 1 2 | 2 | 1 2 | 1 | 1 3 | 1 | 1 | 1 | 1 | 1 2 | 1 +|---|---|---|---|---|---|---|---|---|---| -25 -20 -15 -10 -5 0 TEMPERATURE (C) Schnell and Vali found that the less well decomposed the material the less ice nuclei could be extracted from it. Green organic material contained some ice nuclei but putting microbes to work on it helped a lot. They also found that aerobic decomposition was much better than anaerobic decomposition in making ice nuclei and indirectly crash-bang thunderstorms! They also found that the further along the decomposition was the more low temperature ice nuclei produced. Decomposed litter from years past had nuclei that worked around -5 C. Less ancient organic matter required temperatures of -15 to -20 C. Old humus makes rain-making clouds at higher cloud temperatures. Actually they also found that on about the 7th day of decompositon of green poplar leaves nuclei were produced that caused freezing of water droplets at only -1.3 C and that these kinds of ice nuclei were abundant through the 20th day of decomposition. Schnell and Vali also found that the ice nuclei material was volatile. They also found that mechanical lifting (by wind for sure) put ice nuclei into the air. As part of their thoughts on the significance of their work they note the role of the biosphere in rain-making. In the spirit of our organic times the also note that perhaps using ice nuclei extracted organic matter instead of using mildly toxic heavy metals and silver idodine for rain-making would be EV (environmentally correct.) Urea another compound of "natural origin" could also be sprinkled from airplanes to make rain! Volunteers? ***************************************************************** ***************************************************************** *** *** *** *** *** Schnell and Vali Return *** *** *** *** *** ***************************************************************** ***************************************************************** Schnell and Vali were so excited by their 1972 Nature paper that the paid a return visit in 1973. "World-wide Source of Leaf-derived Freezing Nuclei" -- Nature 246:212-213. More info from them. The found as many as 10 to the 10 (e-mail doesn't like superscripts) nuclei per gram of decaying leaf material but that was only .1% of the total of decaying material. The size of the particles was between .1 and .05 microns. Only about one particle in the atmosphere in 1 million is an ice nucleating particle. Temperatures in excess of 60 C deactivates the stuff. Exciting for me was their finding that the amount of nuclei produced by a member of a given genus depended on what climate zone they harvested the plant material from. Poa (a grass of course) or other genera from Koppen climate zone produced much more ice nuclei than Poa from Koppen climate zones A or C. Well, is it that Poa changes its composition so that different ice nulei were produced in the various cliamte zones or perhaps the microbes doing the decomposition controlled that. Well even the material might come from the cell breackdown of the microbes themselves. We do know that the surface material of some bacteria can nucleate ice and there is even evidence that a particular gene governs this surface material. Well, why would microbes in different cliamte zones be so refined? Why does it all happen? First a Koppen climate classification refresher. Type A = Average temperature of coolest month 18 C or higher. Type C = Average temperature of warmest month greater than 10 C Type D = Average temperature of warmest month greater than 10 C and of the coldest month 0 C or below. Type A = tropical (e.g. rainforest to tropical savanna) Type C = humid mesothermal (e.g. monsoonal, tropical uplands, Mediterranean) Type D = microthermal (e.g. humid continental to subarctic Now for Figure 1 from Schnell and Vali (1973). My graph below is a summary schematic of Schnell and Vali Figure 1. The three curves in my schematic is represented by three curves each. The three curves are the highest, lowest and median spectra of 12 runs made. In short go and look at the original figure to see just how good the data is. Its good. Y-AXIS IS ACTIVE NUCLEI/g LEAF DRY MATTER IN POWERS OF 10 11 | D | D | D | D | D 10 | D | D | | D | 9 | D | | C | D | 8 | C | D | | C | D 7 | | C | D | | C 6 | | C D | | C | 5 | C D | | C D | A | A 4 | A C D | A | | A C D | 3 | A C D | | A | A C D | 2 | A C D +|---|---|---|---|---|---|---|---|---|---|---|---|---|---| -28 -24 -20 -16 -12 -8 -4 0 TEMPERATURE (C) Production of nuclei from leaves were very similar within Koppen climate zones across a wide range of genera! Now why should that be? Schnell and Vali are puzzled by it. Any ideas? This is all strange stuff. As a broad rule the heights of thunderstorms in A are higher than in C and higher in C than in D. The thickness of the troposphere in A is greater than in C and greater in C than in D. This may sound odd and then some but if in the thick atmosphere of the tropics (A) you had the abundance of ice nuclei producing capacity the clouds would rain out before they got to mix surface air all the way to the top of the troposphere where it must get to carry earth's abundant equatorial momentum and energy eventually northward to balance the tropics against the deficits of the high latitudes. If all the thunderstorms [aka hot towers by the tropical meteorologist] were short (clouds don't grow much higher after ice nucleation takes place) the atmosphere couldn't get its transport work done the way it does. Well lets speculate on the subarctic and points north (type D). If the ecosystems of type-D land couldn't carry thier own in terms of production of ice nucleating particles, and given the troposphere (where all the weather action is) is not so thick, you might have trouble making snow you would just have supercooled water droplets in the air. Without ice nuclei they could be as cold as -40 C with no problem. What a bummer of a state for this once-in-awhile glacial world. Glaciers would be made of layers of glaze not compacted snow. What if you just got supercooled rain up there. It falls as liquid rain and freezes on contact with ice nucleating surface or on other ice already formed. Think of the traffic accidents that would happen if every time it was supposed to snow we had freezing rain because the ecosystem wouldn't cough up enough ice nuclei into the air! Most of our LTERs are in category D the leaves from which are good high producers of ice nuclei. This rather long CED effort on my part is put on the table for all you free thinkers out there to scratch your heads and wonder if and why? Have fun. ***************************************************************** ***************************************************************** *** *** *** *** *** TULIP TREE: FROST FIGHTER FIRST CLASS *** *** *** *** *** ***************************************************************** ***************************************************************** From previous CED editions you know that things that make the air wetter have the effect of elevating dewpoint temperatures and thus the expected daily minimum temperature. Tulip trees are such things. Here in Virginia the forests are in leaf by the end of April to the first week in May. Not all years are alike. The Tulip tree leafs out in the last week in March or first week in April. So the air wetting job it does elevates morning temperatures and fights off frosts. In Virginia the last date of killing frost is about the time that all species are leafed out. I am trying to find out if that is true elsewhere or everywhere. That is does the frost free season begin when the trees are leafed out because they the can then fully wet the air and ward off Jack Frost. After all there is still enough cold, dry air in Canada that makes it way south to provide dry enough air with low enough dew points to frost us up pretty good. One would have to wait until about the end of the first week in June to eliminate that prospect. Lets get back to the tulip tree. At the canopy height of tulip trees, the end of the first free season is about 30 days earlier than at the ground. Nocturnal inversions on cold clear nights mean it gets warmer as you go up. So the frost free season ends in the canopy first and then the tulip tree does its thing. Our other, more selfish or less altruisitic species, go into their sex act and flower and fruit in the canopy frost free zone during April and leaf out in late April and early May. Tomatoes can then be planted. In landscapes of topographic diversity the date of the last frost varies considerably. Piedmont Virginia is such a diverse place. In my county, the growing season is only 190 days in "frost pockets" and 270 days at Monticello. There are places around 1500 feet elevation where we have recorded in one year the last killing frost on January 3. My garden dies on the average on October 20. So a student, Jeff Kirwan, in my class on vegetation controls on climate set out to see if the tulip tree really makes all that much difference. He was a properly skeptical student. He bought $180 worth of max-min thermometers and set out for vineyards surrounded by tulip trees. Who protects the vines from frost? He sold all the thermometers to his class mates and his wife let back into the house. Everyone should have a max-min thermometer. Jeff's data is preliminary. Its the kind of stuff from which hypotheses are formulated. ***************************************************************** ***************************************************************** *** *** *** *** *** LTER AT PACLIM MEETING *** *** *** *** *** ***************************************************************** ***************************************************************** LTER was well represented at the recent Ninth Annual Pacific Climate (PACLIM) Workshop April 21-24. The workshop focuses on climate variability of the Eastern North Pacific and Western North America. This year the theme was Long-Term Monitoring. Several LTER scientists were invited speakers. Fred Swanson (AND) gave an overview of the LTER program and later talked about global change research in the Andrews Forest. David Greenlan described climate studies in the LTER program. Climate and hydrology issues were discussed by Douglas Kane (ARC). Manuel Molles (SEV) presented results from research on biome transitions at the Sevilleta site. There were other guest speakers from Scripps, USGS, and the NPS. Although biased we believe that the LTER program was well portrayed.