Question
The Bergeron-Findeisen process of droplet growth involves
The correct answer is
ice-crystal growth in mixed phase clouds
Bergeron-Findeisen Process Explained
The Bergeron-Findeisen process is a key mechanism for precipitation formation in the atmosphere.
It specifically describes how ice crystals grow much faster than liquid droplets in mixed-phase clouds. These clouds contain both supercooled water droplets (liquid below 0°C) and ice crystals.
Mechanism Details
- In mixed-phase clouds, the saturation vapor pressure over ice is lower than over supercooled water at the same sub-zero temperature.
- This difference causes water vapor to deposit onto ice crystals (deposition) and sublimate from liquid droplets.
- Consequently, ice crystals grow rapidly by consuming vapor from the surrounding air, while liquid droplets shrink or evaporate.
- These growing ice crystals eventually become large enough to fall as snow or melt into rain if they pass through warmer air layers.
Reasoning for Correct Option
Option 3, 'ice-crystal growth in mixed phase clouds', accurately defines the Bergeron-Findeisen process. The other options describe different cloud microphysical processes:
- Collision and coalescence (Option 1) is dominant in warm clouds (liquid droplets only).
- Diffusion and condensation (Option 2) describe general vapor transfer but don't capture the specific supercooled water-ice interaction.
- Coalescence and condensation (Option 4) mixes warm cloud processes with general vapor transfer, missing the core ice-crystal aspect.
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Important Questions from Cloud Physics
- If the typical radius of a cloud droplet is $100$ times less than that of a raindrop, how many cloud droplets make a raindrop?
- Which of the following is true with increasing cloud thickness from $50\text{ m}$ to $10,000\text{ m}$?
- In the natural atmosphere with super-saturation rarely more than 1%, the most common form of nucleation associated with change of vapour to liquid is
- A: Hailstones are formed when graupel particles or large frozen raindrops are present in supercooled clouds
B: Accretion of super-cooled cloud droplets increases with hailstone growth
Given the above two statements choose the correct answer from the following. - Let the typical radius of a cloud droplet be $10 \text{ \mu m}$ and that of a rain droplet be $1 \text{ mm}$. Then, the number of cloud droplets that need to coalesce to form one rain droplet is:
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