lecture 3: Water in the atmosphere 6

Question 1

RAIN DROPLETS: FORMATION BY COALESCENCE

Answer 1

• Occurs in liquid water clouds

* Problem that raindrops will only reach a certain size before becoming unstable

Question 2

RAIN DROPLETS: BERGERON-FINDEISEN MECHANISM

Answer 2

• Responsible for majority of global precipitation.
• Saturation vapour pressure over ice is lower than that over liquid water.
• Leads to situation where there is net evaporation from liquid water droplets at the same time as net deposition onto ice crystals.
• Therefore, in mixed clouds (containing liquid water droplets and ice particles) ice crystals and hailstones will grow at the expense of water droplets.
• Hailstones will grow until their weight overcomes cloud updrafts.