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Why hoarfrost in the morning

  1. Jan 8, 2004 #1
    I was wondering how it comes that we have hoarfrost in the morning. Water has his tripplepoint at 0.001°C and 10³Pa, so subblimation occurs at lower pressure and temperature. But we have atmospherical pressure of 10^5Pa, so how comes we have hoarfrost?

    http://www.lsbu.ac.uk/water/phase.html

    I think it has something to do with partial pressure (Law of Dalton), but I'm not sure how...
     
  2. jcsd
  3. Jan 8, 2004 #2
    I could be wrong about the technicalities, but when I have seen hoarfrost(an otherwordly, beautiful site, eh?)on trees, shrubbery, fences, etc... I was under the impression that the primary mechanism involved(other than freezing temps)was supersaturated air.
    Any insight?
     
  4. Jan 13, 2004 #3
    So no one knows why water sublimates at this pressure?
     
  5. Jan 14, 2004 #4

    selfAdjoint

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    Is hoarfrost formed by (reverse) sublimation? Maybe it's only a special kind of condensation, folowed by freezing? What is the dewpoint right next to the leaves or whatever where the hoarfrost forms?
     
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