Newsgroups: lter.ced Path: LTERnet!news From: Bruce Hayden Subject: CED 3.4 April 1994 Message-ID: <1994Apr6.203559.5565@lternet.washington.edu> Sender: news@lternet.washington.edu Organization: Long Term Ecological Research Date: Wed, 6 Apr 1994 19:54:35 GMT ***************************************************************** ***************************************************************** *** *** *** *********** *********** ********** *** *** * * * * *** *** * * * * *** *** * * * * *** *** * ********* * * *** *** * * * * *** *** * * * * *** *** * * * * *** *** * * * * *** *** *********** *********** ********** *** *** *** ***************************************************************** ***************************************************************** Vol.3 No.4 ::::::::::: April Issue :::::::::::: April 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. ***************************************************************** ***************************************************************** *** *** *** *** *** CED: JOINING UP *** *** *** *** *** ***************************************************************** ***************************************************************** The last issue of LTER newsletter advised people wishing to join the CED@lternet.edu mailing list to send an e-mail to Daniel Pommert. The prefered e-mail address for group subscription is CED-request@lternet.edu. Telephone call requests to Daniel are still welcome. There are two main problems with sending requests to Daniel direct: He can lose requests because he gets SO much e-mail and it is the InterNet standard to send e-mail to -request@ to request to subscribe to or be dropped from a list. If you do need to talk to Daniel here is the address you need. The LTER Climate Committee welcomes new subscribers. -- Daniel Pommert. Long Term Ecological Research Network Office dPommert@LTERnet.edu (206)543-1135 -or- 543-7418 ***************************************************************** ***************************************************************** *** *** *** *** *** FAST FALLING FLAKES FUN *** *** *** *** *** ***************************************************************** ***************************************************************** A faithful CED reader, amused by the connection between decomposed organic matter and the kind of snowflakes that form, wanted to know if that also means that biogenic snowflakes fall at special rates. That was nice, smooth aerodynamic thinking. Three types of snowflakes fall by the rule the-bigger-they-are-the-faster-they-fall: graupel, rimed crystals, and needles. Falling graupel [aka snow pellets, soft hail or tapioca snow] is white sleet-like stuff that bounces when it lands and ranges in size from a bit less than 1.5 mm to as big as 5.5 mm. The 1.5 mm graupel falls at about 1 m/s while the 5.5 graupel reaches a terminal earthbound velocity of 2.5 m/s. [1m/s = 2.2 mph]. So 5.5 mm graupel falls at pelting 5.5 mph. Rimed crystals (ice coated ice crystals -- sort of ugly, irregular and non-smooth stuff) start falling out when the reach about 1.5 mm in maximum dimension and they get as big as 4 mm. Their terminal velocities range from 0.8 to 1.1 m/s. The third kind of ice crystals that fall faster the bigger they get are needles. Needles start to fall out of clouds when the are only 0.5 mm in the direction of largest diameter. They get as big as 2.5 mm. The 0.5 mm needles fall (creep) downward at 0.4 m/s while the largest needles fall at 0.6 m/s. A second group of crystals speed to earth in a size-invariant manner. Ice crystals that are plate-like are in this category. They fall at the same speed over their entire size range. They start to fall out of clouds when they reach about 1 mm in size. These six-sided, often glorious dendritic-crystals fall the slowest of all (0.25 m/s) . While graupel pelts you, star-like dendritic crystals just sort of come to rest on you. You might say that biogenic snow crystals formed around 12 C are the most gentle of all snowflakes. You can find these numbers on snowflake fall speed in Cloud Dynamics by Houze, R. A. from Academic Press, (1993). ***************************************************************** ***************************************************************** *** *** *** *** *** RAIN DROP TERMINAL VELOCITY *** *** *** *** *** ***************************************************************** ***************************************************************** Small drops (drizzle size stuff) fall according to Stokes Law, i.e. terminal velocity (maximum velocity reached) is a function of the radius of the drop squared (r^2)! So, where a 0.01 mm drop falls at 0.0001 m/s [I don't think that is even falling]. Actually at this rate it would take some 80 days to reach the ground. A 0.05 mm drop falls at 0.1 m/s. If it were as simple as this then a 1 mm modest sized drop would fall at a hold-on-to-your-hard-hat terminal velocity of something > 10,000 m/s. It is to our good fortune that our world was crafted such that Mr. Stokes and his law don't apply after about .08 mm drop size. Bigger drops fall by Mr. Euler's rule where terminal velocity is proportional to the square root of the radius of the drop (r^0.5). So even a giant 10 mm drop only falls at about as fast as a sprinter sprints: 10 m/s. Even a nylon umbrella can with stand the pounding at this speed. ***************************************************************** ***************************************************************** *** *** *** *** *** THE HAIL AND THE TORTOISE *** *** *** *** *** ***************************************************************** ***************************************************************** Your average hail usually ranges in radius from 0.1 to 0.8 cm. A 1 cm stone has terminal velocities around an ouchy 10 m/s, while to a run-for-your-life or new-car-denting 7-cm radius stone arrives at about 50 m/s (aka 110 mph). We are indeed lucky that hail doesn't fall according to Mr. Stokes Law! Stokes law would demand a 10^10 m/s terminal velocity for our 7 cm hailstone. It is generally thought that hail fall-velocities must occur in the upward direction to get the hail to grow-up to this stout, fast-falling size in the first place. If you get a chance, tell the pilot of your next commuter plane to avoid flying through hail producing thunderstorms! ************** Death by Hail: (source: "It's Raining Frogs and Fishes by J. Dennis (Harper Perennial) ************** "... more died by the hailstones than at the hands of Israel by the sword." Book of Joshua. Goose egg sized hailstones pelted the English army near Paris in 1360 killing hundreds. Shortly there after Edward III signed the Treaty of Bretigny. Three inch hail killed 84 people and 3,000 oxen in the Himalayas in 1853. Cricket ball sized hail near New Delhi in 1888 killed 246 and 1,600 farm animals. A Hunan hail storm killed 200 Chinese and hurt thousands in 1932. Rumanian hen's egg sized hail killed 6 in 1928. The Grecian formula was 22 dead in 1930. In the 1923 newly formed peoples republic (the former USSR)1 and 2 pounders killed 23. A 1930 Lubbock Texas farmer bought it and is the only recorded U. S. citizen to be stoned this way. Hail Alley is near the junction of Nebraska, Colorado and Wyoming. They get 9 to 10 days of hail per year. That is the North American place of record. It makes you wonder why the hail capital of the world (USA) has seen so few deaths. Perhaps the stories are just that: stories. Can't be! Nature magazine, speaker of truths, notes 19 dead in the Northerns Tansvaal. After 30 minutes of precipitation there was hail to a depth of three feet! The dead had to be dug out. Alberta in Can. in July 1953 had 36,000 dead ducks and ducklings. Another hail of hail killed 27,000 more waterfowl. ************** So where is the tortoise in all this hail? In an article you may have missed [(1894) Monthly Weather Review 22:215] we find a report of a hailstone that came to earth with a gopher turtle at its core. There were numerous thunderstorms around Vicksburg, Mississippi on the day of the turtle fall: May 11, 1984. The turtle was 6 by 8 inches and entirely incased in the hail stone. In 1970 a 1.67 lb hailstone 17.5 inches across was found, kept frozen and sent to the National Center for Atmospheric Research (NCAR). I have little trouble with a turtle in a thunderstorm. Temperatures in the upper reaches of a large thunderstorm gets mighty low and a turtle could serve as a giant ice nucleus (the larger the radius of the ice collecting surface the faster it collects vapor from the air) and supercooled water in such a cloud would freeze nicely on the gopher turtle. Hail-speed updrafts could carry the little fellow to great heights collecting layer after layer of ice. So how do you get a a tortoise airborne? Well, a shrew will tumble along the ground with Beaufort wind force of only 4 and a barney-loving child will tumble along at Beaufort force 9. Somewhere in the middle you could get a turtle airborne. If there were a tornado associated with the thunderstorm you could make a hailstone out of Toto! ***************************************************************** ***************************************************************** *** *** *** *** *** POSITIVES AND NEGATIVES ABOUT CLOUDS *** *** *** *** *** ***************************************************************** ***************************************************************** If you are ever lucky enough to make a balloon ascent through a thunderstorm with an electric charge meter on board, your would find the following: The ground is positively charged, the bottom of the cloud, up to where temperature is around -10 C, is rich in positive charges. The middle layer of the cloud from -10 C upward to -20 C temperatures is the layer of negative charge. Above this layer (at still colder temperatures) positive charges rule. The -10 to -20 C temperature range is called the "charge-reversal temperature" [Houze, R. A. 1993. Cloud Dynamics, Academic Press]. Hey, I am not making this up. Cloud micro-physists are still arguing about the why it gets to be this way. In the lab they find that graupel (that is the fast falling ice stuff) takes on a negative change in the -10 to -20 range and is positively charged when it is at colder and warmer temperatures. One theory to explain all this is called the "precipitation hypothesis." In this theory falling graupel takes on a negative charge and leaves behind, at the top of the cloud, little non-falling positively charged ice crystal. The big, falling crystals take on the negative change and the small ice particles left behind take on what is left the positive charges. All this makes for charge separation and large potential gradients (the stuff of lightening). At warmer temperatures (warmer than -15 C the grauple takes on positive charges thus the warm bottom of the cloud gets its positive charge. Another hypothesis is called the "convection hypothesis" [Houze, R. A. 1993. Cloud Dynamics, Academic Press]. In this idea, the upper cloud gets its positive charge due to the harvesting of positive charges from the surface and the planetary boundary layer. Updrafts do this work. Positive charges from the boundary layer are abundant. Biogenic hydrocarbons (terpines and hemiterpines) agglomerate to form petroleum spheres. When 14,000 terpine molecules or so accumulate in a spherical drop (a haze particle) it has a positive charge. In a thunderstorm these biogenic particles are lifted into clouds and play a role in the electrical life of the thunderstorm. Storms without a source of such charged biogenic materials from the surface layer and without biogenic nuclei (e.g. for example marine clouds) rarely have lightening. Over the last year I have become interested by the notion that emissions from the biosphere play so many roles in the cloud physics: cloud condensation nuclei, ice nuclei, and electric charge and contributing to cloud heights, rainfall rates, drop size, snowflake type and fall rate, cloud colors, and charge separation and lightening in clouds. We should not confuse playing a key role with limiting the atmosphere and its dynamics. The biosphere produces the essential emissions in such great quantity that a "poor" terrestrial biosphere is more than up to the job of providing what is needed to make the atmosphere work the way it does. The biosphere provides the essential ingredients for our clouds to do their thing. I do think there are latitude differences in the role of the biosphere and differences between the continents and the oceans. The marine biosphere is very modest in its emissions to the atmosphere and probably does "limit" marine cloud microphysical processes. ***************************************************************** ***************************************************************** *** *** *** *** *** ROADKILLS ON THE ROAD TO DEB *** *** *** *** *** ***************************************************************** ***************************************************************** On my recent drive to my last ecosystem panel meeting, the joy and euphoria lead me to tabulate the frequency of roadkills on my trek to DEB. I used the odometer method. I recorded the distance in miles and tenths between road kill pairs. My transit speed averaged a double-nickle surpassing 65 mph on a four-lane highway. If anything, I probably missed a flat form every so often. I did not tabulate species but skunks, cats, squirrels, dogs, raccoons and crows is roughly the order by abundance. A few notes are in order. Skunks are first on the list. Its spring and the skunk, groggy from the winters rest, are a better harbinger of spring than the robin. Given the number of pickups in Virginia, our proud white tail deer do not remain long on the road. They are soon table-bound. Squirrels, by my observation, tend to be hit by passenger-side wheels. I think they see a car coming and begin serious debate about getting to the other side of the road and make the dash as the car is only meters away. They make the dash just missing the front wheel. They then decide it was a bad idea and return from whence they came only to find that the American car is usually a two axle vehicle and the rear, passenger-side wheel does its thing. I found a corpus every 2.1 miles plus or minus 1.1 miles. That is based on 75 interval measures and in excess of 120 individual squashes. The longest wait I had was 6.1 miles. As a approached environs near Ballston, Virginia and DEB on Route 66, the number road kills dropped off markedly. My hypotheses include: a) Washington drivers brake for animals, b) the HOV (high occupancy vehicles) laws mean that extra riders are at a premium, c) DEB has no cafeteria, d) the efficacy of the suburban animal wardens is outstanding, and e) the visible, on the road duration of a kill is a function of the total number of wheels that pass a point per unit time. I walked the highway near my house and found that bone fragments could be found on the shoulder about every 10 yards. I am not a trained "ostiologist" and besides digs along a highway shoulder is not a way to avoid being a flat fauna yourself. ***************************************************************** ***************************************************************** *** *** *** *** *** IF IT'S WET, HOW WARM CAN IT GET? *** *** *** *** *** ***************************************************************** ***************************************************************** --------------------------------------------------------------------- Average Daily Maximum Temperature (F) in the warmest month of the year at places (equatorial to mid-latitudes) with as much water as need to max-out ET. --------------------------------------------------------------------- Manaus, Brazil 91 (Amazon River Basin) New Orleans, Louisiana 90 (Mississippi Delta) Sandoway, Burma 92 (Irrawaddy Delta) Maturin, Venezuela 91 (Orinoco River Basin) Hasimara, India 90 (Ganges River Delta) Kuang-Chou/Kuang, China 91 (Pai Delta) Karumba, Australia 90 (Gulf of Carpenteria) Homestead, Florida 90 (Everglades) Coquihatville, Congo 90 (Congo River Lowlands) Vang Tan, Vietnam 91 (Mekong Delta) Tocumen , Panama 91 (Canal Zone Waterway) Alexandria, Egypt 87 (Nile Delta) Elizabeth City, North Carolina 88 (Blackwater Drainage) Enachu, British Guiana 90 (Mazaruni River Basin) --------------------------------------------------------------------- This tabulation of forested or densely vegetated wetlands indicates that if you got the water to transpire and the sunlight to power it, your average daily maximum temperature will only rise to about the same as you skin temperature: 90F (32 C). As you warm water and the air over it the amount of water vapor the air can hold increases but not in a linear way with respect to temperature. It follows a exponential track. A calorie of energy put into the water at say 15 C does a bit of evaporation and a bit of sensible heating of the air. At 20 C, the calorie does much more latent heating of the air and not so much sensible heating. At 25 C, the disparity is even greater. At 32 C, well, well read on. This 32 C temperature is most interesting and special. 32 C is the Priestly/Taylor temperature limit for a freely and fully evaporating surface [Priestley, C. H. B. and R. J. Taylor. 1972. "On the assessment of surface heat flux and evaporation using large-scale parameters," Monthly Weather Review 100(2):81-92. As this water temperature is approached, the sensible heat flux to the air goes to zero. So you can't get the air over the water to be warmer than this 32 C. If you find, somewhere, warmer air over water, it must have come from some place else where sensible heating of the air is not so limited by evaporation. I find it interesting that we have a skin and its cooling system that has evolved to have this temperature for our skin and that leaves and forests in full evaporation have the same maximum temperature. Linacre notes that leaves are hotter than air up to 33 C and colder than the air above this temperature. [Linacre (1964) "A note on a feature of leaf and air temperatures," Agricultural Meteorology 1(1):66-72] Anyone who has made hard boiled eggs knows that you can get water hotter than 32 C (watched or not watched); so, what's all this Priestly/Taylor temperature limit stuff? Priestly/Taylor note that in net radiation loads that actually exist in nature, sensible heating becomes negative at 32 C. So you can't get warmer than 32 C without getting unearthly net radiation loads. In the case of our egg-water, we put calories in faster than it can vent them off by evaporation and temperatures rise until the saturation vapor pressure of the air = 1013.25 mb on the average and then there is a riotous boil. In the case of our freely evaporating surface, we have solar radiation input, terrestrial radiation input from the atmosphere, terrestrial radiation output from the water [the addition of these terms = net radiation] and we have sensible and latent heat loss. The net radiation flux equals the sum of the sensible and latent energy fluxes. Priestly/Taylor says that at 32 C net radiations flux = latent energy flux to the air. For maximum earthly and watery net radiation fluxes equatorward of 36 degrees in the warmest month, 32 C is the warmest you can get. Now if you limit latent heat loses (like in a desert) you can drive temperatures higher and higher. The Oceans can't get any warmer than Priestly/Taylor's 32 C with current earthly levels of net radiation. In high summer, you can find sufficiently high net radiations to reach 32 C as far north and south as ~36 degrees. Farther north than that there isn't enough energy to reach the Priestly/Taylor temperature under full evaporation. To get warmer you need to limit ET or blow in hot air from elsewhere. Everywhere equatorward of 36 degrees there is more than enough net radiation to reach 32 C and it doesn't matter about latitude. Poleward of 36 degrees latitude matters. Most ocean areas are not this warm. Few water bodies are. Our "oceans of leaves," however, get to the Priestly/Taylor temperature with regularity. The thermal inertia of leaves, unlike oceans of water, is such that it is the instantaneous net radiation that is critical. The real oceans have very high thermal inertias. The are ponderous in their thermal histories. Leaves heat up and cool down much faster.The specific heat of water is 1 cal per gram per degree C and that of the land ~4 cal per gram per degree C. That it takes four times as many calories at 20 C to heat a gram of water 1 C than it does to heat a gram of land 1 C. The oceans warm up and cool down slowly.