V. Moisture

1. states
1. solid
2. liquid
3. vapor
2. processes
1. melting, evaporation, sublimation
2. freezing, condensation, deposition (sublimation)

1. absolute humidity - mass of water in a given volume of air (gm/m3)
2. relative humidity - Temperature dependent

   amt. moisture x 100
   max. capacity

   1. as T increases, relative humidity decreases (fig. 6-6)
   2. as T decreases, relative humidity increases
   3. when RH = 100% reach saturation and condensation overwhelms evaporation
3. dew point

1. dew or frost - on plants and ground
2. fog - why low? (fig. 6-15)
   1. just base of cloud layer
   2. more dust for nucleating
   3. valley fog from an inversion on cold nights, the cold ground cools the lowest few meters by conduction so below dew point
3. clouds
   1. formation
   • air rises
   • as air rises, it expands and temperature decreases (adiabatic cooling; volume change, not adding or removing heat)
   • as it cools, the relative humidity rises causing condensation
   2. types of clouds fig 6-13
      • cirrus - high altitude, wispy, ice crystals
      • stratus - layers or sheets
      • cumulus - vertical piles with flat base, puffy, indicates instability of rising air
4. Causes of uplift (precipitation)
   1. convectional (warm air rises; unstable)
   2. orographic lifting fig. 6-18
   3. frontal lifting fig 7-6
5. Precipitation
   1. snow starts frozen, falls frozen
   2. rain
      • starts as rain, ends as rain
      • starts frozen, melts while falling
   3. sleet - starts as liquid, freezes while falling
   4. hail - repeated lifting and accretion by updrafts