ESCI 1010 Weather and Climate
Chapter 7 Notes
Collision-Coalescence Process
• Occurs in warm clouds (temperatures above 0°C throughout the cloud)
Bergeron Process
• Occurs in cold clouds (temperatures below 0°C throughout the cloud) and cool clouds
(temperatures above 0°C in the lower portions only)
Rain
• Rain
o Liquid drops >= 0.5 mm
• Drizzle
o Liquid drops <0.5 mm
• Virga
o Visible rain shafts, but rain evaporates before reaching the ground
• Showers
o Brief and sporadic rain
Rain Drops
• Not teardrop-shaped
• Initially spherical, but flatten out on the bottom as they fall
• Wind resistance can further deform the bottom of the drop
• Final shape described as a parachute to a loaf of bread
Snow
• Warmer temperature => wet snow with big flakes
• Colder temperature => dry snow with small flakes
Lake Effect Snow
• Heat and moisture from a warm lake is transferred to an overriding cold and dry air mass
• Once the air mass reaches the other side of the lake, it is humid and unstable
• Speed convergence of wind from lake (faster) onto the land (slower) also aids in lift
Graupel
• Forms when snow encounters supercooled cloud droplets in the atmosphere => ice crystals
form instantly on outside of snow until snowflake no longer identifiable
• Soft ice pellet usually oblong in shape and fragile enough to fall apart when touched
• Also known as “soft hail” and “snow pellets”
Freezing Rain and Sleet
• Sleet
o Forms when raindrops freeze in the air while falling => ice pellets
• Freezing Rain
o Forms when raindrops freeze on contact with Earth’s surface => glaze of ice
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Chapter 7 Notes
Collision-Coalescence Process
• Occurs in warm clouds (temperatures above 0°C throughout the cloud)
Bergeron Process
• Occurs in cold clouds (temperatures below 0°C throughout the cloud) and cool clouds
(temperatures above 0°C in the lower portions only)
Rain
• Rain
o Liquid drops >= 0.5 mm
• Drizzle
o Liquid drops <0.5 mm
• Virga
o Visible rain shafts, but rain evaporates before reaching the ground
• Showers
o Brief and sporadic rain
Rain Drops
• Not teardrop-shaped
• Initially spherical, but flatten out on the bottom as they fall
• Wind resistance can further deform the bottom of the drop
• Final shape described as a parachute to a loaf of bread
Snow
• Warmer temperature => wet snow with big flakes
• Colder temperature => dry snow with small flakes
Lake Effect Snow
• Heat and moisture from a warm lake is transferred to an overriding cold and dry air mass
• Once the air mass reaches the other side of the lake, it is humid and unstable
• Speed convergence of wind from lake (faster) onto the land (slower) also aids in lift
Graupel
• Forms when snow encounters supercooled cloud droplets in the atmosphere => ice crystals
form instantly on outside of snow until snowflake no longer identifiable
• Soft ice pellet usually oblong in shape and fragile enough to fall apart when touched
• Also known as “soft hail” and “snow pellets”
Freezing Rain and Sleet
• Sleet
o Forms when raindrops freeze in the air while falling => ice pellets
• Freezing Rain
o Forms when raindrops freeze on contact with Earth’s surface => glaze of ice
1
