How does hoarfrost form in the morning?

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In summary, the conversation discusses the phenomenon of hoarfrost in the morning and questions why it occurs despite atmospheric pressure being higher than the triple point of water. One possible explanation is that it is due to supersaturated air and the process of sublimation. However, the exact mechanism and dewpoint at which hoarfrost forms is still unclear.
  • #1
Reason
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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...
 
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  • #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?
 
  • #3
So no one knows why water sublimates at this pressure?
 
  • #4
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?
 

1. Why is there hoarfrost in the morning?

Hoarfrost forms when water vapor in the air comes into contact with a cold surface, causing it to freeze and form ice crystals. In the morning, the temperature drops and the air becomes more humid, providing the perfect conditions for hoarfrost to form.

2. How does hoarfrost form in the morning?

When the air temperature drops below freezing, the water vapor in the air condenses and forms tiny ice crystals on surfaces. These crystals grow larger and combine to form hoarfrost, which can be seen in the morning when temperatures are typically at their coldest.

3. Why is hoarfrost most common in the morning?

Hoarfrost is most common in the morning because the air temperature is typically at its lowest point, allowing the water vapor in the air to easily freeze and form ice crystals on surfaces. Additionally, the air is typically more humid in the morning, providing more moisture for the hoarfrost to form.

4. What causes hoarfrost to melt in the morning?

As the sun rises and the temperature increases, the hoarfrost begins to melt. The heat from the sun warms up the air and surfaces, causing the ice crystals to turn back into water vapor and evaporate. Additionally, as the day goes on, the air becomes less humid, making it more difficult for hoarfrost to form.

5. Is hoarfrost in the morning dangerous?

In most cases, hoarfrost in the morning is not dangerous. However, it can create slippery conditions on roads and sidewalks, so it is important to use caution when walking or driving in areas with hoarfrost. It can also damage plants and crops if it forms on them, so farmers and gardeners may take precautions to protect their plants from hoarfrost.

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