Lee, don't forget to bundle up   Robert Leverett   Jan 17, 2005 11:43 PST  Lee: Congratulations (???) on Embarrass Minnesota's 54 below zero reading. Only 11 below. Bob Robert T. Leverett Cofounder, Eastern Native Tree Society Re: Lee, don't forget to bundle up   Lee Frelich   Jan 17, 2005 13:57 PST  Bob: Temperatures in the range of -40 to -45 have been occurring since late December in northern MN. This morning two stations up there had 50 below or colder and there were many reports of -45 to -50. During 1996 it was -60, so these temperatures don't really threaten the record low. The red maples that have been invading the southern margin of the boreal forest during the mild winters of the last few decades will have to think twice about it now. Their deep supercooling strategy to keep cells alive only works to -45 or so. They built Minneapolis were they did for a reason: we are in the banana belt. Big cities don't function well when its -50, so they put Minneapolis in southern MN. It hasn't been any colder than -15 to -20 in the Minneapolis area in the last two weeks, and it has warmed up very nicely each day to 1 or 2 degrees. Lee RE: SOOOPA! winter temps    Lee E. Frelich    Jan 26, 2005 06:40 PST  Ed C, Dale et al.: The actual reason people move to northern MN is so they can pull up a lawn chair and sit outside all night to watch for the exact moment that a tree trunk splits open when it is -50 to -60. You have to pick the right type of tree--black spruce never splits due to cold. This only half joking--some people from northern MN used to live in the condo above me, and they used to sit out on their balcony until midnight, even when it was -20. A few years ago they moved back to Bemidji--there just wasn't enough cold weather in Minneapolis to make them happy. During January 1996, the Weather Service predicted it would reach -60 at Embarrass and Tower MN, and reporters from every TV, Newspaper and radio station in the state went there--and sat outside all night in lawn chairs watching the thermometer. It hit -60 in Tower, but Embarrass didn't make it, so the party was in Tower. They threw a bucket of boiling water in the air and watched it turn to steam and fall to the ground as little crystals. I watched the festivities on TV in my +65 degree living room. The following spring, red oak 'trees' on my nearby Hegman Lake study site had lots of dead spots on the bark, and got even more twisted than they already were. One is at least 170 years old, is 6 feet tall, and its trunk is a mass of scars from frost cracks. Nearby red pine, white pine, balsam fir, paper birch and black spruce didn't seem to have any problems. The 170 year old white pines reach heights of 95 feet even though they are growing on a slab of granite. Lee RE: SOOOPA! winter temps    edward coyle    Jan 26, 2005 07:08 PST  Lee, I looked up Bemidji, as i had no idea where that was, and read they have temps of -50 with 50 mph winds. I have to think that eyes would freeze shut in those conditions. Just a little inhospitable for me. Though I would like to see those protected valleys you spoke of, I'll wait for summer, or fall. Ed C RE: SOOOPA! winter temps    Ernie Ostuno    Jan 26, 2005 07:58 PST  Lee, You may be interested to read a paper titled "Recent State Minimum Temperature Records in the Midwest" from the Bulletin of the American Meteorological Society: Vol. 78, No. 1, pp. 35–40. It goes into some detail of the 1996 record low: http://www.google.com/search?hl=en&q=%22recent+state+minimum+temperature +records+in+the+midwest%22+schmidlin&btnG=Google+Search (click on the "view as html" link in the third listing from the top) excerpts from section 3.e: In anticipation of record cold, the media and other interested persons congregated on 1 February at the home of R. Fowler, the official observer in Embarrass. Two persons familiar with the events, G. Spoden of the Minnesota State Climatologist Office, and meteorologist B. Watson, reported the minimum thermometer in the shelter had been broken for some time at Embarrass but an electronic thermometer had been used in its place. As the temperature descended overnight at Embarrass, the electronic thermometer failed, some said due to all the television cameras and lights plugged into Mr. Fowler’s home, and the temperature record was lost. The media then traveled the short distance to the home of K. Hoppa, observer at Tower 3S. Mrs. Hoppa observed a temperature of −59.5°F (−50.8°C) at 0910 LST, which was rounded to −60°F (−51.1°C) (U.S. temperatures are recorded in whole Fahrenheit degrees). A thermometer in the shelter used for media display purposes by Mrs. Hoppa was then taken from the shelter by a reporter and placed in the nearby swamp where it reportedly read −74°F (−58.9°C).With the failure of electricity at the Embarrass station, tourists visiting there overnight to experience the cold placed two liquid-in-glass thermometers in the shelter and recorded lows of −60°F (−51.1°C) and −61°F(−51.7°C). The reported −74°F in the swamp near Tower 3S cannot be compared to official shelter temperatures since thermometers exposed to the sky will cool far below the shelter air temperature on a clear calm night. ... Mrs. Hoppa reported that −60°F was a more penetrating cold than −40°F, people wore more clothes, cars started poorly, some fuel congealed, there was hardly any traffic, and the governor canceled school throughout Minnesota. Schools were closed for 2 days at Tower. ... As media stunts, one person camped in her lawn overnight, another pounded a nail into wood with a banana left outside in the −60°F cold, soap bubbles were blown to be seen freezing in mid-air, and water was tossed into the air to crackle and freeze before falling to the ground. Birds were reported active around feeders at Tower 3S as the sun rose, in spite of the temperature. Ernie RE: SOOOPA! winter temps    Lee E. Frelich    Jan 26, 2005 13:09 PST  Ernie: Thanks for the article. I wonder if the -74 is real? If swamps really do get that much colder than weather stations, that could easily explain the absence of certain tree species in parts of northern MN. Even if it wasn't -74, but it regularly gets down to -60 in swamps when its -45 or -50 at the weather station, that would exclude several species of trees that I thought should otherwise be able to grow in swamps around Tower, such as red maple, silver maple, yellow birch, basswood, and bur oak. Lee Re: SOOOPA! winter temps   Michele Wilson   Jan 26, 2005 20:21 PST  and I wonder about the lady who slept out on her lawn...did she cheat, use an electric blanket, a sooopa sleeping bag, crawl inside a cow, or brave it and die... Re: cold temps and warm trees   Lee E. Frelich   Jan 27, 2005 06:39 PST  Michele: I think the woman survived, although the lawn is not the best place to spend the night. This type of weather is where certain trees are really handy. White cedar clumps, and black spruce clones (where the branch tips have bent down to the ground and rooted), have relatively little snow under them, which means that heat from the earth rises from the soil, and it is trapped by the dense foliage with snow sitting on top of the crown. You can see dense conifer clumps on infrared aerial photos taken at night--they show up as hot spots. You can crawl in one of those and sleep all night in a toasty -30 degree environment. You might even be joined by chickadees and other wildlife that know where these warm spots are. A friend of mine was camping near Embarrass two weeks ago when it was -54, but on the second night he decided to leave the woods and go into town when his thermometer reached the bottom mark (-45 on his particular model) by 7:00 pm. He didn't know how cold it was, he just knew it was colder than -45, and he had -40 rated equipment. Lee Re: Neil's hypothesis   Lee E. Frelich   Jan 27, 2005 08:04 PST  Bob and Neil: I think you are right about soil freezing impacts on trees. we have a large die off in oaks in central Minnesota in the last two years, and we also had periods of below zero weather with no snow in the last two winters. Frost depths reached 8 feet in some places, and 10 cm soil temperatures reached as low as 7 degrees. Of course we also had a fall drought during 2003, and that probably added to the impact. Lee RE: SOOOPA! winter temps   Ernie Ostuno   Jan 27, 2005 07:24 PST  Lee, The -74 was real only in the sense that the thermometer itself cooled a lot lower than it would have if it were in a shelter. As the article stated: "The reported −74°F in the swamp near Tower 3S cannot be compared to official shelter temperatures since thermometers exposed to the sky will cool far below the shelter air temperature on a clear calm night." Any glass or metallic surface will lose heat faster through radiative processes if it is in the open rather than inside the standardized wooden box used for official temperature recordings. Now having said that, it is likely that any area of lower topography such as a swamp could well be colder than surrounding sites, thanks to "frost hollow" effect. It would have been interesting to have put a sheltered thermometer in that swamp to see how much colder it was than at the observation site. Ernie RE: SOOOPA! winter temps   Robert Leverett   Jan 27, 2005 08:03 PST  Ernie:    I'm confused. Are we saying that the -74 degrees IS the actual air temperature at the point where the thermometer is placed, but that the process of recording temperatures officially shelters thermometers and that leads to warmer temperatures? If so, what is the reason for sheltering other than to get them out of the sun? Bob RE: SOOOPA! winter temps   Ernie Ostuno   Jan 27, 2005 12:50 PST  Bob, I guess you can think of it this way...if you leave a thermometer out in full sunlight, it will heat up above the temperature of a thermometer in a shelter. Similarly, if you leave a thermometer outside on a clear night, it will cool off below the temperature in a shelter. This is because the thermometer is made of materials (glass and metal), which have different radiative properties than wood. This allows those surfaces to cool off faster than wood if they are not sheltered and also to heat up faster if they are exposed to sunlight. You probably have noticed that the windsheild and hood of your car will frost over long before frost forms on most other objects that are not made of metal or glass. The purpose of the shelter is to avoid these temperature extremes caused by the direct radiative heating and cooling of the thermometer itself. Ernie Re: SOOOPA! winter temps   John Eichholz   Jan 28, 2005 04:18 PST  Ed, Bob: As I understand it, the basic process of radiational cooling is the radiation of heat to deep space at night. The clear winter nighttime sky exposes objects to the deep darkness of space, which is very cold. The rate of transfer of heat is always proportional to the temperature difference and the insulation value of the air, thus the rapid rate of cooling experienced by the bulb on very clear nights. Deserts also have that large day/night difference, because the air is so dry (like it is in winter here). In some circumstances, the air just doesn't hold enough ready heat to reintroduce into the bulb of the thermometer by convection, so there occurs a temperature difference. When the sky is cloudy, radiation to (or from) deep space cannot occur as readily, so this effect is absent. Why doesn't the air also cool? Probably because air is a poor radiator compared to glass or metal, and cools, but not as fast. The shelter contains many surfaces not exposed to this cooling process, and is perhaps made of wood ( a better insulator than glass) and is therefore more in equilibrium with the air temperature. Too, radiational cooling is only one reason for a cold night, the other being the introduction of cold air from elsewhere via atmospheric circulation. This air finds its way into the shelter easily keeping it cool. Eventually, the object cools the air, or stops radiating so fast and the air warms the object, and equilibrium is reached. It is perhaps a philosophical point, but all objects are always at different temperatures, since their temperature is always changing in response to the temperature of bodies around them. Even a bowl of soup will always have hotter parts and cooler parts. I think when this stops we'll all be dead -- complete entropy. John Re: SOOOPA! winter temps   John Eichholz   Jan 28, 2005 18:26 PST  Bob: I found a neat NOAA website where they go into the equipment used at a "cooperative weather station", including a picture of a temperature shelter. It is at: http://www.srh.noaa.gov/bro/coopsite.htm John RE: SOOOPA! winter temps/question for Lee   Ernie Ostuno   Jan 30, 2005 17:14 PST  Ed, In this case I think that the surrounding air is actually cooled by being in contact with the metal surface (or glass, or snow for that matter). Think about a surface that is losing heat to space. The temperature will cool due to radiative heat loss and that cooling can be at a much greater rate than the rate the surrounding air is cooling. A case in point...clear, calm nights right after a fresh snowfall are often the coldest of the year. Why? Because snow does two things. First, it reduces the warming effect of terrestial longwave radiation from the ground and second and most importantly, it is very efficient at radiating heat energy to space. The surface of the snow will actually cool the air quite a bit colder than it would get if the snow wasn't there. This effect is not as pronounced on windy nights (unless colder air is being advected in) because the wind mixes the air near the ground with warmer air from above (which hasn't been cooled by being in contact with the snow surface). Conversely, snow is a great insulator. There can be a tremendous temperature gradient from the surface of the snow, where temperatures can be far below zero, to just a few inches below the surface, where temperatures are usually not far below freezing. It is for this reason that I can tell how deep the snow cover was on the side of my house during the winter by the level that my rose bushes sprout back in the spring. Lee, As for radiative properties of different materials...you brought up an interesting point. It would appear that the more cold-adapted tree species such as spruce are less efficient at losing heat through radiation from their surfaces as other trees are. Has anyone looked at the radiative "energy budgets" of different tree species? For instance, I wonder if a tree with smooth bark such as beech would lose heat quicker than a rougher barked oak or hickory. I suppose an infrared sensor could be used to "see" which trees are warmer than others on a cold winter night... Ernie winter temps/question for Lee   Lee E. Frelich   Jan 31, 2005 06:08 PST  Ernie: I have not heard of anyone looking at radiative properties of different tree surfaces for cold tolerances. We have studied insulating properties of bark, and pines have the best insulating capacity because their bark is thickest, and it is a slightly better insulator than bark of other species at the same thickness. However, I think this is probably more applicable to fire survival. Basically, 2.9 times the square of bark thickness in cm predicts the number of minutes that a tree trunk can be exposed to a 500 degree C flame before the cambium underneath will be killed, which in turn requires exposure of living cells to temperatures of 60 degrees C for about 1 minute. For example, of two white pine trees are exposed to flames for 5 minutes during a surface fire, and one tree has 1 cm thick bark and the other 2 cm thick bark, then tree #1 will be girdled by the fire and killed (it can only tolerate about 3 minutes of flame exposure), whereas tree #2 will survive with little damage, since it can tolerate 2x2x2.9 minutes or about 12 minutes of exposure. Bark thickness is greatest at the base of a tree where it is exposed to fire, and it is very thin on the twigs, yet we don't see pines and spruces along the northern edge of their range with dead twigs each spring after an episode of -60 temperatures, which is why I conclude that bark insulation is more important for fire survival than for surviving winter cold. We do see dieback of red maple and red oak after an extreme winter cold spell, but that is known to be due to their deep supercooling mechanism that can only possibly work down to about -47 F. Still, it would be nice to know whether tree surfaces (especially conifer needles) cool down to temperatures above, at, or below the air temperature on calm nights, and whether these effects vary among species and help explain the presence or absence of certain tree species which have very patchy distributions in northern MN. Lee RE: winter temps/question for Lee   Robert Leverett   Jan 31, 2005 07:09 PST  Lee:    This is absolutely fascinating stuff. I image that you all paint of the constant heat exchange that is going on between surfaces that are out in the open makes it seem very strange to me that I ever put so much stock in the "official" temperatures reported from regional airports. Bob   Home