1. How Do the Clouds Form?

2. The global water cycle

3. Ocean water covers 70% of the Earth’s surface

4. More than 1000 major rivers flow on the seven continents Amazon river (#1)Yangtze river (#4)Mississippi river (#6)

5. Water vapor flows in the atmosphere

6. Clouds drifts with the winds

7. Precipitation drives many atmospheric circulations which in turn transport water around the world Hadley Circulation Monsoons Walker Circulation

8. A significant fraction of the human body is water (~75%) The remaining: fat, protein, carbonhydrate, other solids

9. So the water in our bodies may come from … A stream in the Niagara Fall … A white cloud over the tropical Pacific … A dew drop in the Amazon rainforest … Therefore we need to protect the environment because any pollution we put into the environment may someday come back into our bodies An ice sheet in the Arctic Ocean…

10. Movie time! Weather: Wet

11. Water (H 2 O ) is unique on earth because it can exist in all 3 states (phases) 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 Saturation: equilibrium between evaporation and condensation

12. Diabatic processes – add/remove heat –Conduction (e.g. movement of air mass over a cold surface) –Radiation (e.g. cooling of boundary layer air by longwave radiation) Adiabatic processes - no addition/removal of heat –Add water vapor to air –Mix warm air with cold air –Cooling of air parcel when it rises (because air parcel expands when it rises, like a balloon) 1 st Law of Thermodynamics  expanding air cools, compressed warms (like a manual hand air pump). Methods to achieve saturation and condensation

13. Forms of Condensation: saturation  liquid droplets or ice crystals condensation/deposition  dew, frost, fog, clouds

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

15. Clouds Clouds are instrumental to the Earth’s energy and moisture balances Most clouds form as air parcels are lifted and cooled to saturation (Lowering temperature to dew point  cloud formation) Clouds have interesting distributions

16. Satellite observation of clouds - Projects NASA’s International Satellite Cloud Climatology Project (ISCCP) Combine the measurements of 5 geostationary and 1-2 polar orbiting satellites. 1983-Now, cloud top height and optical depth. NASA’s Earth Observation System including a set of polar orbiting satellites (A-Train), especially CloudSat (with a cloud radar) and CALIPSO (with a cloud lidar). Ongoing, cloud particle information, detailed vertical structure.

17. 1) rate of cooling of parcel (unsaturated v. saturated) unsaturated – dry adiabatic lapse rate (DALR) saturated – saturated adiabatic lapse rate (SALR) 2) rate of cooling of surrounding atmosphere environmental lapse rate (ELR): an overall decrease in air temperature with height ELR is measured by weather balloon. Long-term global average ELR = 0.65 o C/100m. Three possible outcomes: 1)absolutely unstable air 2)absolutely stable air 3)conditionally unstable air Static Stability and the Environmental Lapse Rate Static stability – refers to atmosphere’s susceptibility to being displaced Stability related to buoyancy  function of temperature The rate of cooling of a parcel relative to its surrounds determines its ‘stability’ of a parcel

18. Environment Parcel Environment Parcel Environment Parcel The three types of stability Absolutely Unstable Conditionally Unstable Absolutely Stable

19. 1) Entrainment Turbulent mixing of ambient air into parcel Leads to evaporation along cloud boundaries Evaporation uses latent heat, cooling the cloud  reduces buoyancy Courtesy Russ Dickerson, U. Maryland What stops ‘unstable’ air masses from rising indefinitely ? 2) Encountering a layer of stable air (inversion) a rising parcel may reach a stable upper air environment the parcel cooling rate will exceed that of the ambient air the parcel will slowly cease ascension and come to rest at some equal temperature level three types: radiation, frontal, subsidence

20. 1. Cloud top height/pressure 2. Cloud thickness (optical depth) 3. Cloud coverage When clouds comprise more than 9/10th of the sky = overcast When coverage is between 6/10th and 9/10th = broken When coverage is between 1/10th and 6/10th = scattered Cloud coverage less than 1/10th = clear Cloud Properties

21. NASA’s International Satellite Cloud Climatology Project (ISCCP) Cloud Classification - commonly used in climate research

22. Clouds are good reflectors of solar (shortwave) energy and good absorbers of earth’s (longwave) energy. The net effect (cooling or warming) depends on the type of cloud In a changing climate, increases in some types of clouds would promote warming, while increases in others would cause cooling Climate models are limited in how well they can simulate clouds: We don’t know all of the processes that cause clouds Clouds form at scales much smaller than models can resolve Conclusion: clouds cause probably the largest uncertainty in model simulations of future climate. Why do clouds constitute a wildcard for climate change? Stronger Greenhouse effect Stronger Albedo effect

23. Global water (hydrological) cycle Water Vapor Basics (names of different phase changes, latent heat) Two methods of achieving saturation and condensation (diabatic vs. adiabatic processes). Different types of condensation - dew, frost, fog (radiation, advection, upslope, precipitation, steam), clouds. Formation of clouds: 3 types of stability. Two factors limiting the height of clouds. 3 cloud properties. 9 ISCCP cloud types. Summary