Physical GeographyLecture 23

Buoyancy, Stability, Clouds and Fog

A visible collection of microscopic liquid water droplets and/or ice crystals

Clouds

Adiabatic Cooling of Rising Air Condensation and/or Deposition Need something to condense or deposit

upon: ◦ Condensation Nuclei◦ Freezing Nuclei

Formation of Clouds

Cloud Forms

◦ Stratus clouds

◦ Cumulus clouds

4

Figure 6-15b

Figure 6-15c

Cirrus

Cloud Heights

◦ High clouds (> 6 km)

◦ Middle clouds (2 - 6 km)

◦ Low clouds (<2 km)

◦ Clouds of vertical development Can grow up from low

bases to>15 km

6

Figure 6-16

Cirrus (Mare’s Tails)

Cirrocumulus

Altocumulus

Altocumulus Altostratus

Altostratus

Nimbostratus

Cumulus

Atmospheric Stability and Buoyancy

Adiabatic Cooling

Lifting Condensation Level

Stable Air and Cloud Formation

Unstable Air + Cloud Formation

Conditional Instability

Fog

23

Radiation Fogcool, clear, calm nights

Valley Fog – a type of radiation fog

Advection Fog

Upslope Fog

Steam or Evaporation Fog