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Diffusion Deposition: Ice Crystal Growth and Vapor Pressure Gradient

Learn about the process of ice crystal growth through diffusion deposition, where water vapor moves from higher pressure droplets to lower pressure crystals. Discover the optimal conditions for this process and its impact on cloud glaciation.

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Diffusion Deposition: Ice Crystal Growth and Vapor Pressure Gradient

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  1. Diffusion Deposition Diffusion Deposition Diffusion Deposition • At a given temperature, the vapor pressure over a water surface is greater than that over an ice surface. • Due to this gradient, water vapor moves from the higher pressure surrounding the droplets to the lower pressure surrounding the crystals. • Thus, the ice crystals grow at the droplets' expense. This process creates sub-saturation with respect to water, and the droplets evaporate to maintain water saturation, making additional water vapor available for ice crystal growth. • Eventually the pool of liquid water diminishes and the cloud becomes glaciated.

  2. Diffusion Deposition (cont.) • The rate of diffusion is highest where the difference between the saturation vapor pressure between ice and supercooled liquid water is greatest. Optimal growth rates occur near -15°C.

  3. Summary • Layer 1 (Ice Producing): -12C for ice. • Layer 2 (Warm Layer?) • Evaporation or Sublimation Layer? • Layer 3 (Surface) ●0C at surface or lower? ●Can FZRA turn to IP (trend to colder/deeper air)? SN? -12C? ●Tw > 33F possibly rain (greater than 1000ft)

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