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#1
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How saturated adiabatic lapse rate varies with temperature
Following the previous discussion on lapse rate, can anyone point me to
source where I can find out how saturated adiabatic lapse rate varies with temperature? I know that this number increases from 1C/1000' to 3C/1000' as the temperature gets colder, but I would like to see a plot or an equation that describes this behavior. Thanks! |
#2
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"Andrew Sarangan" wrote in message 1... Following the previous discussion on lapse rate, can anyone point me to source where I can find out how saturated adiabatic lapse rate varies with temperature? I know that this number increases from 1C/1000' to 3C/1000' as the temperature gets colder, but I would like to see a plot or an equation that describes this behavior. Thanks! I don't know if I can find you a formula... But you can look at this diagram: http://satellite.usask.ca/mcidas/fram32.gif (It may age, so try to get there quickly. You may want to save the diagram for reference.... it doesn't change... I usually use: http://twister.sbs.ohio-state.edu/skewt.html but for some reason, only the "pick-a-station" map is available, but all picks return error 404 no such page. It may come back to life later. If it does, it will have similar diagrams, only with current real data....) In the usask diagram, look at the curved purple lines. That is the rate of cooling for saturated air (saturated adiabatic lapse rate). Note the temperature lines are light gray, hard to read, leaning to the right. The light gray, slightly curved, leaning "backwards" to the left, are the "dry" adiabatic lapse rates (rate of cooling when lifting unsaturated air). The green lines are the rate of decrease of dewpoints with lift. (The numbers on the green lines are "specific" humidity... grams of water vapour per kg of dry air, related to a specific dewpoint and air pressure) In all cases, if you are at a starting point between lines, you just follow upward, parallel to the lines of interest. If you look at the purple line near plus 28 C at the surface, and lift that air Saturated to 5800 metres (19,000 ft), it will cool to about 2 degrees, averaging about 1.35 deg per 1000. If you start at about minus-5 deg at the surface, and follow parallel to the purple lines to 5800 meters, you get a drop to about -50, or average of about 2.37 per 1000 feet. . These are average cooling over a rather large lift depth. Shorter lifts in the warmest temperatures (bottom right) cool considerably slower, and in the coldest temperatures (top left) they are pretty much parallel to the dry adiabatic rate of cooling.... 3 deg C per 1000. Note that the saturated rate of cooling does not kick in until the humidity reaches 100 percent.... in other words, the dewpoint and dewpoint with be equal.... |
#3
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"Icebound" wrote in message ... Note that the saturated rate of cooling does not kick in until the humidity reaches 100 percent.... in other words, the dewpoint and dewpoint with be equal.... Bah....sorry: "...in other words, the temperature and dewpoint will be equal..." |
#4
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"Icebound" wrote in message ... "Andrew Sarangan" wrote in message 1... Following the previous discussion on lapse rate, can anyone point me to source where I can find out how saturated adiabatic lapse rate varies with temperature? I know that this number increases from 1C/1000' to 3C/1000' as the temperature gets colder, but I would like to see a plot or an equation that describes this behavior. Thanks! I don't know if I can find you a formula... But you can look at this diagram: I found this example of the same tephigram diagram, which may be easier to read that the usask version. Also, the heights are shown in pressure levels at regular intervals, and it may be easier to interpolate intermediate heights ( and easier to convert to feet using standard atmosphere pressure-height conversion). http://www.eos.ubc.ca/courses/atsc20.../tephigram.pdf (http://www.usatoday.com/weather/wstdatmo.htm for standard atmosphere tables) In this particular version: Temperature lines are marked T=10, T=20, etc. Dry adiabatic rate-of-cooling lines are the ones marked with the Greek letter phi. (phi=0, phi=10, etc. phi represents "potential temperature", and phi=10, for example. means that air whose temperature-pressure is anywhere along that line, would reach 10 degrees IF it were lowered to 1000 milibar (hectoPascal) pressure) The saturated adiabatic rate of cooling lines are the long-dashes, curved. In this particular version, they stop them at the -40 temperature line, probably with the idea that beyond that, the rate-of-cooling can be considered to be pretty much the same as the dry-adiabatic rates. And the lines along which the dewpoints decrease are dotted... and again, are labelled with the specific humidity values. |
#5
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"Icebound" wrote in message ... In this particular version: Temperature lines are marked T=10, T=20, etc. Dry adiabatic rate-of-cooling lines are the ones marked with the Greek letter phi. (phi=0, phi=10, etc. ............. Okay, so I forgot my Greek for a minute.... All "phi" in the post was supposed to be "THETA", of course. |
#6
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http://www-frd.fsl.noaa.gov/mab/soundings/java/ "Andrew Sarangan" wrote in message 1... Following the previous discussion on lapse rate, can anyone point me to source where I can find out how saturated adiabatic lapse rate varies with temperature? I know that this number increases from 1C/1000' to 3C/1000' as the temperature gets colder, but I would like to see a plot or an equation that describes this behavior. Thanks! |
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