1. Global Water Cycle and Atmospheric Moisture

2. Video: Weather – Wet

3. The global water cycle
Water is unique on earth because it can exist in all 3 phases, and the phase changes can release latent heat to drive weather/climate

4. Flow of water vapor in the atmosphere

5. Paintings of water vapor
Corot: Ville D'avray ( )

6. Flow of >1000 rivers on the seven continents
Mississippi river
Amazon river
Yangtze river

7. Paintings of rivers
Jin Nong (金农): Moon river ( )

8. Flow of ocean currents

9. Snow/Ice cover provide a reservoir

10. A significant fraction of the human body is water (~75%)
Every 16 days nearly 100% of the water in a human body is exchanged.
The remaining: fat, protein, carbonhydrate, other solids

11. So the water we drink may come from …
Therefore we need to protect the environment because any pollution we put into the environment may someday come back into our bodies

12. Video: Weather – Wet

13. Phase changes of Water (H2O )
An H2O molecule
3 states (gas, liquid, solid) depending on how the molecules are connected together
Can change from any state to any other state. Latent heat is consumed or released in a phase change
e.g. Evaporation -> liberation of water molecules, requires energy

14. Indices of Water Vapor Content
Humidity: amount of water vapor in air
Humidity expressed in a number of ways  Indices
Vapor Pressure (e): the partial pressure exerted by water vapor.
Mixing Ratio (r): mass of water vapor (g) relative only to mass of dry air (kg) (in g/kg).
Relative Humidity (RH): the amount of water vapor in the air relative to the possible maximum.
Dew point temperature: temperature at which saturation occurs in air (generally colder than Tair, equals to Tair when saturated)
RH=e/esx100

15. Saturation and Condensation
Molecules escape into the overlying volume as water vapor during evaporation. Energy must be available at the water surface. Water vapor increases in air as surface water evaporates.
Water vapor molecules randomly collide with the water surface and bond with adjacent molecules during condensation.
There is an equilibrium between evaporation and condensation during saturation. Upon saturation, evaporation rate equals condensation rate.
Same thing happens between water vapor and underlying ice surface: sublimation/deposition.

16. Dependence of saturation on temperature
Saturation vapor pressure – maximum amount of water vapor that the atmosphere can hold at a given temperature
Saturation vapor pressure increases with temperature, i.e., warmer air can hold more water vapor.
Saturation vapor pressure for ice is smaller than that for water. Therefore, when ice crystals and water drops co-exist, water vapor tends to condense onto ice rather than onto liquid water.

17. Methods to achieve saturation and condensation: Cooling down the temperature
Diabatic processes – add/remove heat
Conduction (e.g. movement of air mass over a cold surface): dew, frost, advection fog
Radiation (e.g. cooling of boundary layer air by longwave radiation): radiation fog
Adiabatic processes - no addition/removal of heat
Cooling of air parcel when it rises (because air parcel expands when it rises, like a balloon): upslope fog, clouds
1st Law of Thermodynamics  expanding air cools, compressed warms (like a manual hand air pump).

18. Different types of fog found throughout the U.S.

19. Summary Global water cycle
Water Vapor Basics (names of different phase changes, latent heat)
Humidity indices
Saturation vapor pressure increases non-linearly with temperature
Saturation vapor pressure for ice is smaller than that for water
Two methods of achieving saturation and condensation (diabatic vs. adiabatic processes). Different types of condensation - dew, frost, fog (advection, radiation, upslope), clouds.

20. Works cited