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Why doesn't water freeze when there are clouds?

  1. Jan 5, 2016 #1
    hi everyone
    I'm new here.
    Need some time to adjust.
    I'm from Kashmir.
    In winter water on earth freeze when sky is clear,but if there r clouds out there water does not freeze.
    Why is it so?
     
  2. jcsd
  3. Jan 5, 2016 #2

    phinds

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    Do you understand the 3 forms of heat transfer?
     
  4. Jan 5, 2016 #3
    yes i do.
    Convection conduction n radiation.
     
  5. Jan 5, 2016 #4

    phinds

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    OK, and what are the characteristics of radiation from surface water to the sky on cloudless days vs cloudy days?
     
  6. Jan 5, 2016 #5
    u mean radiation will be reflected back by clouds
     
  7. Jan 5, 2016 #6

    phinds

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    I mean I want you to think about what radiates and in what direction.

    Let me give you a discussion that may at first not seem related to your issue. There was a statement on another post some time ago that a body in space does not radiate any heat if it is below 3.7degrees absolute because that is the average temperature of space (caused by the CMB). I had to explain to the poster that this was totally wrong. The NET result of radiation into and out of such a cold body is towards the body because it radiates at a lower temperature than its surroundings and so gains heat from its surroundings but that does not mean that it does not radiate. How might all this apply to your issue?
     
  8. Jan 5, 2016 #7
    Yes that is right.
    So wht is answer of my question
     
  9. Jan 5, 2016 #8
    Usually when its very cold there is much less humidity and hence less clouds.
     
  10. Jan 5, 2016 #9

    phinds

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    You are missing my point. Giving people answers is boring. Helping people learn how to think and how to get answers themselves is interesting. I have been trying to get you to figure it out for yourself. It appears that you are not interested in doing that and just want an answer. Having the answer is not going to be of any real use to you. Knowing how to figure out the answer would be very useful.
     
  11. Jan 5, 2016 #10

    phinds

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    And in what way does that help answer the question, given that he posited that, under the conditions of interest, there ARE clouds?
     
    Last edited: Jan 5, 2016
  12. Jan 5, 2016 #11
    Sorry!
    Correct me if i m wrong.
    Everything above absolute zero radiates.
    So wht happens during clouds is that water radiates in upward direction,but at the same time it absorbs radiation emitted by clouds with the result it won't freeze.
     
  13. Jan 5, 2016 #12

    Evo

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    If the temperature gets low enough for long enough, water will freeze, clouds or no clouds. Some things to consider is the depth of the water, the movement, a shallow freshwater pond will freeze much faster than a deep fast moving stream.
     
    Last edited: Jan 5, 2016
  14. Jan 5, 2016 #13

    phinds

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    Exactly. Good job.

    It's a somewhat delicate balance. If the air is cold enough it will freeze anyway and if the air is too warm it won't freeze, but when it's on the border that extra push of not getting any radiation from the clouds is enough to let it freeze.

    EDIT: I see Evo beat me to it on that part :smile:
     
  15. Jan 5, 2016 #14
    Thanks
    i got it now.
     
  16. Jan 9, 2016 #15
    It's not quite that simple. I believe that the OP asked why cloud droplets did not freeze even though their temperature might be below 0°C. Cloud droplets are quite often at temperatures well below 0°C. Meteorologist consider temperatures of about -40°C to be the "icing point" in cumulonimbus clouds. This is the temperature/elevation at which the icy "anvil" forms. Above that temperature, cloud droplets will usually remain liquid. Pure water is extremely difficult to freeze. I believe that Molinero {2011 University of Utah] found that such water would remain liquid until a temperature of -48°C was reached. Luckily, terrestrial water is never pure. Impurities called "icing nucleii" will cause surface water to freeze at temperatures up to 0° (and even higher is special circumstances). In the atmosphere, icing nucleii are harder to come by, and water usually will remain liquid until sufficient icing nucleii show up or lots of icing ions (H15O7+) are formed. Water is not a simple substance.
     
  17. Jan 9, 2016 #16

    phinds

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    No, he specifically did NOT ask that. He asked about water on the ground.
     
  18. Jan 9, 2016 #17
    phinds said (post#16):

    "No, he specifically did NOT ask that. He asked about water on the ground."

    You're very emphatic for someone who obviously hasn't read the title of the post. It asks, "Why doesn't water freeze inside clouds?" Am I missing something in that question?

    post #13: "It's a somewhat delicate balance. If the air is cold enough it will freeze anyway . . ." This is simply not true. Throughout the atmosphere, cloud droplets remain liquid even though they and the air around them are both "below freezing". It's a very common phenomenon, which any meteorologist (or pilot) will verify. The freezing of cloud droplets is not automatic, but depends upon a considerable number of contributing factors. Temperature is just one of them. The free atmosphere is not the laboratory, things are different there.
     
  19. Jan 9, 2016 #18

    Evo

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    You apparently read the thread title and not the post. The member's first language is not English, but he clarified that he was speaking of water on the ground.

     
  20. Jan 10, 2016 #19
    Evo,

    I read both the title and the post. His English is better than my Urdu, but--because of the title--I thought that the water in his phrase "clouds out there" referred to the water in the clouds. Shall we compromise and agree that both questions are valid and worthwhile scientific questions?

    Any farmer will tell you that "clear nights are frostier than cloudy ones". The primary reason is that much of the outgoing IR is intercepted by cloud cover--especially in the 10 micron IR "window". The clouds, in their turn, radiate IR back to the surface. This is incoming thermal radiation that is not present under clear skies. Hence, cloudy nights are often warmer than clear ones--other things being equal. This situation does not apply during the day, when reflection of sunshine often outweighs emission of thermal IR.
     
  21. Jan 10, 2016 #20
    Yes i have made a mistake in writing title in hurry.
    N yes that is a separate question.
    N thanks for ur precious time
    i got my answer.
     
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