16. Schematic view of the molecular structure of water in its three physical states and heat-energy exchange among those states. The latent heat-exchange numbers between the arrows are explained in the text (values are for 0°C). Phase Changes of Water, Latent Heat Heat is consumed in evaporation, melting; heat is released in condensation, freezing (sublimation).

17. Variation of saturation vapor pressure (mb) with temperature (  C). The curve is nearly a pure exponential. At temperatures below 0  C saturation values over supercooled water are greater than over ice. Measurements of water vapor Vapor pressure is the pressure exerted by water vapor molecules Saturated vapor pressure is maximum pressure of water vapor at that temperature Dew point is the temperature the air must be cooled to reach saturation Relative humidity is ratio of water vapor in air to maximum the air can hold at that temperature. RH is usually highest when daily temp- erature is lowest. Specific humidity is the mass of water Vapor in the air per unit mass of air. Mixing ratio is the mass of water vapor in The air to the mass of dry air containing the Water vapor.

18. Hydrologic cycle. The numbers attached to the stages express each value as the volume of water divided by Earth surface area. Thus the values shown represent the depth of water (centimeters per year) associated with each mass transfer. All can be directly compared to the global average precipitation rate, which is about 100 cm/year. Fig 12.2

19. Distribution of water in the hydrosphere. The middle and lower bars show the percentage distribution of the 2.8 percent of total hydrospheric water that is fresh. Of that freshwater component, only about one-tenth is easily available to humans. Water in the Hydrosphere Most of the water is salt water in the ocean Most of the fresh water is locked up in ice sheets and glaciers Most of the liquid fresh water is in the ground Fig 12.3

20. Total water withdrawals (millions gallons per day) for the United States in 2005. Water Usage in the United States, 2005 Which states use the most water?

21. Condensation near the ground forms fog, a cloud in contact with the ground. As the ground and surface air cools to the dewpoint, water vapor condenses into a radiation fog (cooling by longwave radiation overnight) here in East Africa.

22. Schematic diagram of the different cloud types – stratus, cumulus, and cirrus, arranged by their typical altitude. Cloud Types

23. Precipitation Processes The Ice-Crystal Process-requires the coexistence of ice and super-cooled water droplets in the cloud. Ice grows at the expense of water droplets that evaporate water molecules which adhere to the ice until they are large enough to fall as snow. If the air is warm enough, the snow melts and rain occurs. The Coalescence Process-requires different sizes of water droplets within warm clouds. Larger droplets grow by falling faster and sweeping up smaller droplets by coalescing until they are large enough to fall as rain. Source: http://collider.com/singin-in-the-rain-60th-anniversary-blu-ray-review/191992/http://collider.com/singin-in-the-rain-60th-anniversary-blu-ray-review/191992/

24. Four major forms of precipitation. (A) A rainstorm douses the Ponderosa Pine Forest near Flagstaff, Arizona. (B) Falling snow accumulates in south-central Alaska. (C) Freezing rain forms an icy coating on pine needles on a golf course in Wawona, near Yosemite National Park, California. (D) Golf-ball-sized hailstones litter the countryside following a storm in northern Texas. Besides rain and snow, there is: Sleet-melting ice that refreezes before reaching ground Freezing rain-melting ice that freezes on contact with a frozen surface Hail-ice particles that grow within clouds that have strong updrafts Graupel-soft, partially melted hail Source: http://climate.met.psu.edu/features/Hail/ PEMA_hail.php http://climate.met.psu.edu/features/Hail/ PEMA_hail.php Types of Precipitation

25. Four Forms of Precipitation A B C D A-rainstorm B-snow C-freezing rain D-hail

26. Range of water balance conditions found at the surface of Earth. (A) Baghdad, Iraq, experiences a constant deficit because potential evapotranspiration normally exceeds precipitation. (B) At Tokyo, Japan, the situation is reversed, and a constant water surplus is recorded. (C) At Faro, Portugal, the intermediate situation occurs, with a combination of surplus and deficit at different times of the year. Water Balance for Different Climates

27. Water Balance Averages by Latitude Average annual latitudinal distribution of precipitation, evapotranspiration, and runoff in cm per year. The arrows show the direction of the water vapor flux by the atmospheric circulation.

28. Global distribution of annual evaporation and evapotranspiration in centimeters, with land elevations adjusted to sea level. Red isolines show the pattern over land; blue isolines over the oceans. Global Distribution of Annual Evaporation, Evapotranspiration Fig 12.10?

29. Global Distribution of Annual Precipitation Global distribution of annual precipitation in millimeters/day. Source: http://www-das.uwyo.edu/~geerts/cwx/notes/chap10/global_precip.htmlhttp://www-das.uwyo.edu/~geerts/cwx/notes/chap10/global_precip.html