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Thread: Average temperature of the atmosphere

  1. #1 Average temperature of the atmosphere 
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    Does earth's atmosphere have an average temperature?
    I ask this because i'm wondering about the intensity of the atmosphere's natural glow of infrared radiation.

    Thank you


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    WYSIWYG Moderator marnixR's Avatar
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    i'd be inclined to say no, at least as a real temperature, just like the average person doesn't really exist

    however, as a mathematical construct there's no reason why it couldn't exist
    what this average means in reality depends on how you calculate the average


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  4. #3  
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    Quote Originally Posted by marnixR
    i'd be inclined to say no, at least as a real temperature, just like the average person doesn't really exist

    however, as a mathematical construct there's no reason why it couldn't exist
    what this average means in reality depends on how you calculate the average
    Now marnix, you know that an "average" anything doesn't exist. But if emetzner's poorly phrased question could be properly answered the answer would be...

    "Averages give insight into general observations about specific events."

    Don't you think?
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    WYSIWYG Moderator marnixR's Avatar
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    i'm always wary of the use of averages, since they are by definition abstractions
    sometimes they tell you something worthwhile knowing about how the world fits together, sometimes they don't - until the question is more specific it's hard to say which category this one falls in
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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  6. #5  
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    Sorry about this, I know I shouldn't have asked such an ambiguous question. It's just i've recently been reading a book from the 'a newscientist guide' series and it confused me by stating that the temperature of the atmosphere is 300 K. I don't know how they managed to work that out, but I assumed they must be going by some kind of calculation of average. I'm just interested if anyone knows something about this.

    Thanks
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    WYSIWYG Moderator marnixR's Avatar
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    sounds a bit like a ball-park figure than an accurate measurement
    it could be the averaging out of annual average surface temperatures, but until you know exactly what average of what type of measurement, that's as much a guess as the next one
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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  8. #7  
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    Quote Originally Posted by marnixR
    sounds a bit like a ball-park figure than an accurate measurement
    it could be the averaging out of annual average surface temperatures, but until you know exactly what average of what type of measurement, that's as much a guess as the next one
    Thinking the same thing. The area average surface temperature over a year is about 289K.

    Getting at an average atmosphere temperature would depend a lot over what you're averaging: over the entire depth? Over a specific defined hieght? The bottem of the atmosphere obviously matches the surface, while the very top go over a 1500 K but are so rarified that molecules seldom collide.
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    The temperature of the atmosphere varies dramatically according to altitude, and rapidly falls well below zero Celsius with gain in height. I am assuming that the question really means, "What is the average temperature at sea level?"
    Answer 15 C.
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  10. #9  
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    For those who want real, factual data about Earth's atmospheric temperatures, I strongly suggest reading this article in the online Citizendium encyclopedia:

    Milton Beychok
    (Visit me at www.air-dispersion.com)
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    Quote Originally Posted by mbeychok
    For those who want real, factual data about Earth's atmospheric temperatures, I strongly suggest reading this article in the online Citizendium encyclopedia:

    from the citation above:
    This is a draft article, under development and not meant to be cited, but you can help improve it.

    These unapproved articles are subject to a disclaimer.
    Better, I think, to strongly suggest going to source.
    The temperature profile used in that article is sourced from NOAA -

    http://www.srh.noaa.gov/jetstream/atmos/atmprofile.htm
    An average temperature profile through the lower layers of the atmosphere. Height (in miles and kilometers) is indicated along each side. Temperatures in the thermosphere continue to climb, reaching as high as 2,000C.
    you'll note it reads: "An average" not "The average" ...


    Quote Originally Posted by emetzner
    It's just i've recently been reading a book from the 'a newscientist guide' series and it confused me by stating that the temperature of the atmosphere is 300 K. I don't know how they managed to work that out, but I assumed they must be going by some kind of calculation of average. I'm just interested if anyone knows something about this.
    300 K ... ~27C / ~81F ... seems a tad warm for the global average at surface ...

    One widely accepted figure is 288 K (or ~15C / ~59F), though exactly how that is determined I haven't learned. That is the number used by UCSC to calculate the so-called greenhouse effect -

    from - http://ic.ucsc.edu/~acr/ocea80b/Assign1Blackbody.pdf
    For a blackbody that absorbs all of the suns radiation (no reflectivity) we set A = 0. This gives us a blackbody temperature: Tb = 278K = +5C.

    The real Earth actually reflects 30% of incoming solar radiation. By setting A = 0.3, we get a temperature that is lower: Ta = 255K = -18C. This calculation tells us that an albedo of 0.3 causes 23C of cooling (relative to Tb).

    The actual temperature of the Earth is 15C. Since this is 33C more than Ta, then the greenhouse effect produces 33C of warming.
    Nature abhors perfection; cats abhor a vacuum.

    "I don't know; I'm making it up as I go ..." Dr H Jones (Jr).
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  12. #11  
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    Cran:

    Is there something wrong with using a chart sourced from NOAA and the National Weather service? Your comments seem to belittle them as a source.

    That article in the Citizendium online encyclopedia also mentions that the Earth's surface temperature is taken to be 14 to 15 degrees C (with 4 source references).

    Isn't it a bit pedagogical to make a distinction between an "average" value and "the" value? And to make it seem to be wrong to use an average value?
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  13. #12  
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    Quote Originally Posted by mbeychok
    Cran:

    Is there something wrong with using a chart sourced from NOAA and the National Weather service? Your comments seem to belittle them as a source.
    Quite the contrary -
    Better, I think, to strongly suggest going to source.
    The temperature profile used in that article is sourced from NOAA -
    means exactly what it says; that NOAA is the correct source to cite,
    rather than a wiki clone which states quite clearly on the page you had "strongly" recommended:
    This is a draft article, under development and not meant to be cited, but you can help improve it.

    These unapproved articles are subject to a disclaimer.
    The formatting of that statement is theirs - the bolded words (on the website) are links to further explanations.

    Publicly-controlled and public consumption media are not required to take responsibility for the accuracy or reliability of the information presented therein. Nor are they required to distinguish between facts, conclusions, speculations, or interpretations.

    Encyclopaedias and similar "ready references" are good starting points for researching information, but their real value is in the source references - where the information is presented in its original context, and some assessment of the author's credibility (and the information's relevance to your research) can be made.

    That's the point I tried to make, but which was somehow misinterpreted.

    I made no comment either way regarding the National Weather Service - I would consider the National Weather Service to be a very good source of information; a much better source than someone else's interpretation of that information.

    Quote Originally Posted by mbeychok
    That article in the Citizendium online encyclopedia also mentions that the Earth's surface temperature is taken to be 14 to 15 degrees C (with 4 source references).
    Yes - whether ~287-288 K, ~14-15C, or ~58-59F, they do seem to be the most widely accepted or presented estimates.

    Again, though, it would have been better to check the references.

    1st reference-
    http://www.bambooweb.com/articles/e/...tmosphere.html
    BambooWeb Dictionary Open Content Encyclopaedia
    The average temperature of the atmosphere at the surface of earth is 14 C...

    This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License
    Assessment: no explanation and unreliable source.
    ...........


    2nd reference-
    http://nssdc.gsfc.nasa.gov/planetary...earthfact.html
    Earth Fact Sheet (NASA)
    Black-body temperature (K) 254.3

    Average temperature: 288 K (15 C)
    Diurnal temperature range: 283 K to 293 K (10 to 20 C)

    Author/Curator:
    Dr. David R. Williams, dave.williams@nasa.gov
    NSSDC, Mail Code 690.1
    NASA Goddard Space Flight Center
    Greenbelt, MD 20771
    Assessment: no explanation; generally reliable source; author contact if required
    ............


    3rd reference-
    http://www.ncdc.noaa.gov/oa/climate/...lies/index.php

    Global Surface Temperature Anomalies
    National Oceanic and Atmospheric Administration
    National Climatic Data Center


    ... The figures are based on 1961-1990 estimates from the University of East Anglia's Climate Research Unit (UEA-CRU). The recently derived 1961-1990 global monthly surface temperature averages represent, in our opinion, the best absolute estimates of global mean temperature and were compiled at UEA-CRU by M. New, P.D. Jones, D.E. Parker and others. The data and methods used are described in the Monthly Gridded Time Series and in current and forthcoming publications...

    Absolute estimates of global mean surface temperature are difficult to compile for a number of reasons... Consequently, the estimates below, while considered the best available, are still approximations and reflect the assumptions inherent in interpolation and data processing...

    Combined Mean Surface Temp. Annual 1901 to 2000 (C) 13.9
    Combined Mean Surface Temp. Annual 1901 to 2000 (F) 57.0

    Last Updated Monday, 17-Aug-2009 12:18:31 EDT by Ahira.Sanchez-Lugo@noaa.gov
    Please see the NCDC Contact Page if you have questions or comments.
    Assessment: detailed explanations provided with further references; generally reliable source; editor and organisation contact if required

    ..........

    4th reference-
    http://oceanworld.tamu.edu/resources...ionbalance.htm
    Our Ocean Planet: Oceanography in the 21st Century - An Online Textbook

    Earth's Radiant Energy Balance and Oceanic Heat Fluxes

    Earth's average surface is 32C warmer than it would be if it had no atmosphere. A planet the size of earth at earth's distance from the sun, and in thermodynamic equilibrium with solar energy (sunlight), would have an average surface temperature of -18C. Earth's mean, global surface temperature for the period 1901 to 2000 is 13.9C, which is 32C warmer. This increase in temperature is due to greenhouse gases in earth's atmosphere...

    Department of Oceanography, Texas A&M University
    Robert Stewart Contact - stewart@ocean.tamu.edu
    Assessment: key statement uncited; references for other aspects; generally reliable source; author contact if required

    ............

    Once again, NOAA is the best source, and therefore the best reference.


    Quote Originally Posted by mbeychok
    Isn't it a bit pedagogical to make a distinction between an "average" value and "the" value?
    Only if you're not interested in the distinction between science and speculation; if the context and explanatory information don't matter, then you can present any information in whatever way you please.

    Actually, I was making a distinction between "an" average and "the" average.

    In this particular instance, the authors are indicating that the diagram is an illustrative example, not the definitive product. Given that the average profile varies (in temperature and height) according to latitude and base surface, the mean global atmospheric temperature profile may, or may not, resemble the example provided. To simply assume that it does is risky because the assumption is not supported in the original text.

    Quote Originally Posted by mbeychok
    And to make it seem to be wrong to use an average value?
    Please, can you indicate where I have done this?
    Nature abhors perfection; cats abhor a vacuum.

    "I don't know; I'm making it up as I go ..." Dr H Jones (Jr).
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