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Thread: (Layman Science Series) Week 1 - Why are mountain tops icy?

  1. #11
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    Two main process convection/winds and adiabatic expansion


    Note: an atmosphere is needed for this process
    Note: valleys are sometimes uneven, rigged, inclined, thus inclination is not cause
    Note: incident radiation is not cause by itself, if anything mountain tops can receive more radiation because atmosphere is thinner there


    [1 mark] awarded to say "hot air rises". Not needed to break it down as much as I have done. It is not required to go below high school physics but I just want to be thorough)

    1. Photons from the sun heat the earths surface more than the atmosphere. (This happens in valleys and on moutains, by itself is not cause)
    2. Ground heats air in contact by conduction.
    3. Heated air expands and is less dense and thus rises. (Consider tiny bubbles of hot air rising in a big liquid of cooler air)
    4. Bubbles of warm air grow to form bigger "convection currents" (The bubbles are heated more isothermal and does work to dispace air. This displaced air is a form of potential energy. So yes, there is some advance details of energy transfer beyond my scope)



    [1 mark] to say "rising air experience a pressure drop"
    5. Not only convection currents are formed, but winds on a bigger scale causing more air to flow
    6. Pressure is greater at the valley than at the mountain top because more atmosphere gases is on top of the valley than mountain top. Air that mores upwards experience a change in pressure.

    [1 mark] to say "adiabatic expansion occurs mostly on air that experiences a pressure drop"
    7. Adiabatic expansion occurs mostly on air that experiences a pressure drop, all the way on it as it rises. Similar to releasing the air from a tire.

    [1 mark] to say "this adiabatic expansion causes a drop in temperature of the air"
    8. This adiabatic expansion causes a drop in temperature of the air. Then by conduction, the mountain top gets cooled. (Can end here)
    9. Air that falls to fill the new gaps does the reverse.
    10. The air that is heated by the mountain top surface also rises, but the atmosphere is thinner there. Air that replaces that gap does less relative to the valley. The valley gets no cooling from this process and tends to be hot even when winds blow, while the mountain top get natural A/C. Yes, there are thermodynamic "energy transfers" in play, and entropy increasing, but that is beyond me and more tertiary level meteorology.

    Note: Winds that blow up the mountain would have a similar effect

    [1 bonus mark] to say why temperature decrease when the air expands adiabatically
    {Later I post}
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  2. #12
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    I'm sick - so couldn't follow up. Again I'm surprised more people didn't attempt this.

    For the bonus - I'll say that things expand when heated but contract when cooled. Since there is no heat transfer in thermodynamics, something else happens. I'll leave it there.
    Knowing the solution doesn't mean knowing the method. Yet answering correctly and regurgitation are considered "learning" and "knowledge".

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