Which process explains rain formation from ice crystals in clouds?

Which process explains rain formation from ice crystals in clouds?

• A. Hydrometeor Process
• B. Bergeron-Findeisen Process
• C. Nucleation Process
• D. Coalescence Process

Answer: (B)

In clouds that contain both ice crystals and supercooled liquid droplets, rain forms mainly through the Bergeron-Findeisen process. This relies on the fact that the saturation vapor pressure over ice is lower than over liquid water, so water vapor tends to move from the supercooled droplets to the ice crystals. The droplets evaporate while the ice crystals grow, causing the ice crystals to become larger. Eventually these crystals fall; if they pass through warmer air below freezing, they melt into raindrops, producing rain. The other processes describe different precipitation paths—coalescence involves collisions of liquid drops in warm clouds, while nucleation is about the initial formation of droplets or ice crystals—but they don’t explain rain formation via growth of ice crystals in mixed-phase clouds the way the Bergeron-Findeisen process does.

In clouds that contain both ice crystals and supercooled liquid droplets, rain forms mainly through the Bergeron-Findeisen process. This relies on the fact that the saturation vapor pressure over ice is lower than over liquid water, so water vapor tends to move from the supercooled droplets to the ice crystals. The droplets evaporate while the ice crystals grow, causing the ice crystals to become larger. Eventually these crystals fall; if they pass through warmer air below freezing, they melt into raindrops, producing rain. The other processes describe different precipitation paths—coalescence involves collisions of liquid drops in warm clouds, while nucleation is about the initial formation of droplets or ice crystals—but they don’t explain rain formation via growth of ice crystals in mixed-phase clouds the way the Bergeron-Findeisen process does.