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What happens inside a cloud?
Micro-scale Processes - Ice Crystal Formation
Ice
nuclei are relatively sparse,
compared with condensation nuclei. Fortunately, there is another important
mechanism for ice crystal growth that occurs in the mixed layers of a cloud,
where ice and water coexist. This mechanism is called vapor diffusion.
Molecules escape the surface of water much easier than they escape the surface
of ice, resulting in more molecules above a water droplet. The extra molecules
make the
saturation vapor pressure just
above a water surface greater than the saturation vapor pressure above an ice
surface, which means it is easier for the ice crystal to grow.
Therefore, if an ice crystal and water droplet are near each other, water vapor
molecules will migrate from the droplet toward the ice crystal. The ice crystal
can then grow, using the water vapor that has evaporated from the water droplet.
This growth process is maximized at -15 to -12 C (5 to 10 F).
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Micro-scale processes - snow formation
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Micro-scale Processes - Ice Crystal Formation
Ice
nuclei are relatively sparse,
compared with condensation nuclei. Fortunately, there is another important
mechanism for ice crystal growth that occurs in the mixed layers of a cloud,
where ice and water coexist. This mechanism is called vapor diffusion.
Molecules escape the surface of water much easier than they escape the surface
of ice, resulting in more molecules above a water droplet. The extra molecules
make the
saturation vapor pressure just
above a water surface greater than the saturation vapor pressure above an ice
surface, which means it is easier for the ice crystal to grow.
Therefore, if an ice crystal and water droplet are near each other, water vapor
molecules will migrate from the droplet toward the ice crystal. The ice crystal
can then grow, using the water vapor that has evaporated from the water droplet.
This growth process is maximized at -15 to -12 C (5 to 10 F).
