Transcript PPT

rdry= 0.1
0.22
0.48 m
Assumes supersaturation=0.05%, p=900 hPa, T=273K
Tropical
profile
THERMAL DIFFUSION
LIMITED
VAPOR DIFFUSION LIMITED
Polar profile
ICE FORMATION AND
CONDENSATIONAL GROWTH
PRECIPITATION
Terminal velocity of drops
terminal velocity [m s-1]
• Balance between gravitational force (= mg) and
drag force ( size)
• Time taken for drop to reach terminal velocity is very
short
r1/2
r
“precipitating”
r2
“non precipitating”
radius [µm]
All collisions
Collisions only for S1 drops:
“autoconversion”
Collisions between S1 and
S2 drops only: “accretion”
Collisions only for S2 drops only:
“self-collection”
Ice crystal aggregates in Cirrus clouds
• Taken using an
imaging probe on
an aircraft
• Most crystals show
irregular
aggregated shape
• Snow in
midlatitudes mostly
grows by
aggregation
Westbrook et al. 2004