Fog

Discussion in 'Free Thoughts' started by timojin, Jan 17, 2017.

  1. timojin Valued Senior Member

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    How does a fog forms and stays
     
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  3. paddoboy Valued Senior Member

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    Fog is simply "cloud' that forms close to the Earth's surface,

    https://en.wikipedia.org/wiki/Fog
    Fog forms when the difference between air temperature and dew point is less than 2.5 °C or 4 °F.[5]

    Fog begins to form when water vapor condenses into tiny liquid water droplets suspended in the air. Six examples of ways that water vapor is added to the air are by wind convergence into areas of upward motion;[6]precipitation or virga falling from above;[7] daytime heating evaporating water from the surface of oceans, water bodies, or wet land;[8]transpiration from plants;[9]cool or dry air moving over warmer water;[10] and lifting air over mountains.[11] Water vapor normally begins to condense on condensation nuclei such as dust, ice, and salt in order to form clouds.[12][13] Fog, like its elevated cousin stratus, is a stable cloud deck which tends to form when a cool, stable air mass is trapped underneath a warm air mass.[14]

    Fog normally occurs at a relative humidity near 100%.[15] This occurs from either added moisture in the air, or falling ambient air temperature.[15] However, fog can form at lower humidities, and can sometimes fail to form with relative humidity at 100%. At 100% relative humidity, the air cannot hold additional moisture, thus, the air will become supersaturated if additional moisture is added.

    Fog can form suddenly and can dissipate just as rapidly. The sudden formation of fog is known as "flash fog".[16]

    Fog commonly produces precipitation in the form of drizzle or very light snow. Drizzle occurs when the humidity of fog attains 100% and the minute cloud droplets begin to coalesce into larger droplets.[17]This can occur when the fog layer is lifted and cooled sufficiently, or when it is forcibly compressed from above by descending air. Drizzle becomes freezing drizzle when the temperature at the surface drops below the freezing point.

    The thickness of a fog layer is largely determined by the altitude of the inversion boundary, which in coastal or oceanic locales is also the top of the marine layer, above which the air mass is warmer and drier. The inversion boundary varies its altitude primarily in response to the weight of the air above it, which is measured in terms of atmospheric pressure. The marine layer, and any fogbank it may contain, will be "squashed" when the pressure is high, and conversely, may expand upwards when the pressure above it is lowering.
     
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  5. timojin Valued Senior Member

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  7. timojin Valued Senior Member

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    What is the difference between rain and fog . this is what I am driving.
     
  8. paddoboy Valued Senior Member

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    The same difference between rain and cloud I would imagine.
     
  9. exchemist Valued Senior Member

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  10. timojin Valued Senior Member

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  11. paddoboy Valued Senior Member

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  12. timojin Valued Senior Member

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    The fog droplets fall to the ground at the same rate as rain droplets ?
    Is the air mixed at higher concentration in the fog droplet as in the air droplet ?
     
  13. DaveC426913 Valued Senior Member

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    Fog droplets do not fall to the ground. They are suspended in the air.

    Here's a diagram showing the relative size, showing why rain falls but fog and clouds do not.

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    Last edited: Jan 17, 2017
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  14. SereneCalm Registered Member

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    According to science, when water vapor condenses into tiny liquid water droplets suspended in the air , fog begins to form. For your better understanding of what causes fogs. You may read what I got as a reference below.

    Notes to read: http://www.weatherquestions.com/What_causes_fog.htm
     
  15. timojin Valued Senior Member

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    Thank you and Dave I have seen and posted the sizes of droplets and nucleating droplets . A question remains in me. Is there air dissolved in the droplet no matter how small she is. Since at one point so to say the vapor as is formed can be said the water is dispersed or to say is dissolved in air . then as the droplet grows the air is displaced up to a point gravity overcomes and rain will fall.
    Come on guys strike my hypothesis.
     
  16. exchemist Valued Senior Member

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    I honestly do not know why you have to make such a meal out of this. Water dissolves oxygen and nitrogen to a very small degree, but this is quite irrelevant to the issue of water droplets falling. You seem to be trying to edge towards some stupid notion that somehow the density of the water in the droplets changes, but that's crap. It is simply to do with size. As I said earlier, we went through all this at some length in your earlier thread that I linked to in post 6. We discussed the effects that compete with gravity and why these have more effect on small droplets: air currents, Brownian motion et), we made the comparison with smoke, i.e. small solid , rather than liquid, particles which show the same tendency to remain suspended in air, yet you still seem unable to take in what happens. I do not understand what blocks you from seeing it.
     
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  17. paddoboy Valued Senior Member

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    I do.

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  18. origin Heading towards oblivion Valued Senior Member

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    The answer to your question is yes.
    Water vapor is the gas phase of water. That means that the water is in the form of individual water molecules. The water gas mixes with the other gases in the atmosphere.
    The weight of the water droplets overcomes the force of air currents.
    What hypothesis? How do you strike it?
     
  19. DaveC426913 Valued Senior Member

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    The air in the droplet is not displaced. It is suffused with air - full of N2 and O2 just like any other small body of water is.
    You haven't proposed one.
     
  20. Janus58 Valued Senior Member

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    The small droplets are suspended by updrafts in the cloud. As the droplets grow they reach a point when the updrafts are not enough to support them and they fall. This has nothing to do with any change in density of the drops but is a result of the square-cube law. If a droplet increases it diameter by some factor, it increases it surface area by the square of that factor and its volume by the cube of that factor (if a droplet doubles in diameter, it surface area increases by 4 and its volume by 8)
    Since the upward force exerted on a drop by the updraft is proportional to it surface area, the upwards force increases slower than the volume/mass of the droplet. Eventually, the weight of the droplet increases to the point where its more than the upward force. The greater the updraft, the larger the drops that can be suspended before they fall as rain.

    Thunderheads have extreme updrafts. So much so that they will toss the droplets so high that they freeze, the frozen droplets fall back through the cloud picking up more moisture, and be tossed back up again to add a new layer of ice. This will continue until the frozen droplet either become too heavy or is thrown free of the updraft. It then falls as hail. The updrafts in thunderheads can throw hail stones for distances of miles from the thunderhead, and at times can produce hailstones the size of tennis balls (I was once stuck in one of these hail storms as a kid.)
     
  21. timojin Valued Senior Member

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    Were does the updraft force come from ?

    You are implying that the particle while moving up is collecting more and more particle and coalescing takes place up to certain size ?
     
  22. Russ_Watters Not a Trump supporter... Valued Senior Member

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    Wind.
    Yep.
     
  23. Janus58 Valued Senior Member

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    All kinds of sources. Wind being deflected upward by terrain, rising warm air created by surface heating, etc. One of the things they teach you when you take flying lessons is that while clouds look nice and soft and fluffy, the air turbulence in and just below them is not something you want to fly through.
    Yes, that is about the gist of it. It also can take place after they start to fall as drop bump into each other on the way down.
     

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