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B Strange Phenomena when the Sun is low on the horizon?

  1. May 9, 2016 #1
    I live about 1/4 mile from the Interstate Highway. I am far enough away the traffic can not be heard until the sun is very low on the horizon. Every even for about 1 hour when the sun is very low it sounds like the interstate traffic is in my back yard. It is so loud it is just like standing next to the highway. Once the sun goes on down traffic can not be heard.

    Also I built a very good TV antenna. I receive 46 crystal clear station from 40 miles away. The antenna is over kill on purpose no matter how bad the weather gets, rains, snows, fog, hail, tornado, wind, trees, nothing blocks the signal we get crystal clean TV reception. But every day for about 1 hour when the sun is very low on the horizon TV reception for several station is zero and other stations break up too bad to watch.

    What does the sun have to do with these 2 strange phenomena?
     
  2. jcsd
  3. May 9, 2016 #2

    A.T.

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    Could be refraction:
    http://hyperphysics.phy-astr.gsu.edu/hbase/sound/refrac.html
    https://www.ec.gc.ca/foudre-lightning/default.asp?lang=En&n=4EFD3A52-1
     
  4. May 10, 2016 #3
  5. May 10, 2016 #4

    sophiecentaur

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    It may be worth while explaining how it works. The speed of sound is roughly proportional to the temperature. When there is cold air near the ground an warm air above, the waves overhead travel faster than the waves along the ground and this has a focussing effect which bends the sound energy that normally goes way over your head and brings it down to ground again.
    There's a similar effect when the wind is blowing towards you and there can be a velocity gradient (lower speed air near the ground due to drag and higher wind speed at height) This also has a focussing effect due to a very small phase advance in the sound travelling at height and is not, as people say, because the sound is 'blown towards you'.
     
  6. May 10, 2016 #5

    A.T.

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    Not primarily, because winds are much slower than the speed of sound. But it also has a slight effect.
     
  7. May 10, 2016 #6

    sophiecentaur

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    What wind speed were you considering? What is "slight"? Isn't the main effect that you're referring to a difference in propagation time (which is what causes the focussing))
    The focussing effect due to wind shear is significant.
     
  8. May 10, 2016 #7

    A.T.

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    And longer propagation time means the energy is distributed over a larger area, thus decreasing intensity.
     
  9. May 10, 2016 #8

    sophiecentaur

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    Inverse square law. Yes it must be there and possibly measurable. How far does the ISL 'sphere' move, I wonder? The effect would be in the ratio of sound speed to speed difference (squared, probably). But the very audible difference must be in the region of a few dB so it has to be 'geometrical' focussing effect due to the distortion of the sphere rather than its actual speed of movement.
     
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