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Question about temperature measurements

  1. Jul 22, 2007 #1

    Simfish

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    Used in measured highs/lows/hourly temperatures.

    Are they shade temperatures or temperatures under the Sun? Also - are shade temperatures really cooler than temperatures under the Sun?
     
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  3. Jul 22, 2007 #2

    Gokul43201

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    Yes, they are shade temperatures, and yes, these are often much lower than a reading under direct sunlight. A temperature measurement under direct sunlight will only tell you the temperature of the thermometer itself, not the air temperature.
     
  4. Jul 22, 2007 #3

    Bystander

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  5. Jul 22, 2007 #4

    Gokul43201

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    When I was in high school, they used to call those things Stevenson Screens.
     
  6. Oct 22, 2007 #5
    All official measurements are taken about 1.5 meters above the ground, in a white shelter that is ventilated at a certain rate. The white color (ideally) gives the shelter a very high albedo, close to 100%, which means that it won't absorb sunlight and warm up... the ventilation keeps the air mixed and fresh (think greenhouse effect, or lack thereof).

    Unfortunately, this can lead to problems... you can imagine that shelters don't stay perfectly white throughout their existence, for instance.
     
  7. Oct 23, 2007 #6

    Bystander

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    What rate is that? When was such a specification added? How are "corrections" made for "unventilated" data collected prior to that time?

    For the record, there is no ventilation rate specified; there are forced ventilation shelters available, but they are not in common use.

    "100%?" "Certain conditions and restrictions apply. Substantial penalties for early withdrawal, or in other random events." This is for chalk, clay, lead, or titanium whites? Oil, resin, lacquer, enamel, or latex bases? 5800 K emissivities run 0.1 - 0.3; 300 K emissivities run 0.6 - 0.8; temperature rises can get to 5 - 10 K in still air.

    Meteorological temperatures are NOT true air temperatures; they are a combination of true air temperature and wind speed.
     
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