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Cool and hot days in summer?

  1. Nov 25, 2007 #1
    Suppose in summer, two consecutive days, the first was hot at 30 centigrade, the second at 20 centigrade. Both was cloudless in the afternoon. There haven't been any rain prior to the days nor after for about a week.

    What caused the second day so much cooler then the first even though they looked identical. How would the UV radiation compare for both days. I assumed that since the second day was so much cooler, no sun protection was needed. Is that wrong?
     
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  3. Nov 25, 2007 #2

    PhanthomJay

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    Unless you live near the ocean, where a sea breeze can drastically drop temperatures from one day to the next, temperatures differences are largely due to jetstream and steering current patterns which move weather systems across the globe. Might be tropical air from the South on one day, and dry cool air from the North on another.
    yes, quite wrong. The UV index is calculated from a number of factors, the most important of which is the cloud cover. All other factors being equal, the cloudless days may yield the same UV index regardless of temperature. UV radiation in summer is highest around mid-day, when the sun is highest.
     
  4. Nov 25, 2007 #3
    I live about 40km to an ocean so that might explain the temperture difference.
     
  5. Nov 25, 2007 #4
    What are the fundamentals? The temperture differences are due to different type of air. Hot temperture implies air that are oscilating very quickly. Vice versa for cool temperture. So the energy that allows oscilations in the air are from other sources other then the sun? What are the sources?
     
  6. Nov 25, 2007 #5

    PhanthomJay

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    No, that's a bit too far for such a large temperature difference. Sea breezes are usually confined to within just a few kilometers of the coastline. The difference is likely due to e different air mass.
     
  7. Nov 25, 2007 #6

    PhanthomJay

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    Atnospheric/oceanic interactions, which influences the jetstream.
     
  8. Nov 25, 2007 #7
    Air moves. A lot. Check out the weather forecast on TV. Given the same conditions vis a vis cloud cover and rain etc, does not mean that the conditions are true for areas east, or west. A transition overnight from a low pressure zone to a high pressure zone (or vice versa?) could well give you the same apparent weather in terms of cloud cover and relative humidity, but completely different temperatures.

    BTW. Sun protection has nothing to do with air temperature. It has to do with exposure to solar radiation. 20 degrees in the dense shaded woods means low sun protection needed relative to the days reading. 20 degrees same area at the beach means much more protection required. (reflection off the water and sand....)
     
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