Extratropical Cyclones (and Anticyclones)

Question 1

Cyclone development stages

Answer 1

1. Developing stage (t=0)
   - boundary (front) separating cold and warm air
   -upper-level disturbance moves over front, causing wave along front to form
   - heavy precipitation along the front
2. Mature stage (starts at t=~24h)
   - wave on front intensifies, warm air replaces the space left behind by the moving cold front
   - cold front moves faster than the warm front causing cyclonic circulation
   - lowest pressure is located at centre of wave
3. Dissipating stage (starts at t=~48h)
   - cold front catches up to warm front, warm front slides above cold front since it is not dense enough, forming a loop.
   - loop eventually closes as entire cyclone is composed of the cold air mass (occlusion)

Question 2

Sleet

Answer 2

partially melted snowflakes fall through shallow layer of warm air and then refreeze as they fall through a freezing layer of air above surface

Question 3

Freezing rain

Answer 3

occurs when snowflakes descend into a warmer layer of air and melt completely
- when liquid water drops enter freezing air above surface they dont have time to freeze
- once they hit surface they will freeze if surface is also freezing

Question 4

Temp profile of snow

Answer 4

• entire profile must be at or below 0 so no melting occurs

Question 5

Temp profile for sleet

Answer 5

Freezing zone in clouds followed by shallow warm layer above 0 which melts the snow. Cold layer near surface partially re-freezes it.

Question 6

Temp profile for freezing rain

Answer 6

Cold layer in clouds where snow forms, deep warm zone where snow melts to form liquid water, small cold zone above surface allows the water to hit ground as liquid but freeze upon contact