MET 2204 METEOROLOGY

1. MET 2204METEOROLOGY Presentation 5: Moisture, Cloud Formation, & Precipitation. Presented by Mohd Amirul for AMC

2. Recapitulate • Lets recap what we have done last week: • What is the Wind? • Concept of Convection • How the air move? • Use of Isobar • The force acting on the wind: PGF, GF, Friction • Major Wind: Geostrophic and Gradient Wind • Jet Stream • Local and Minor Surface Wind: mountain and Valley; Katabatic; Land and Sea. • Wind Shear Presented by Mohd Amirul for AMC

3. Presentation Outline • Introduction • Water Vapor • Change of State • Cloud Formation • Cloud Identification. • Precipitation • Land and Water Effects • Conclusion Part 1 Part 2 Presented by Mohd Amirul for AMC

4. Learning Outcomes • At the end of this session, student should be able to: • Identify the physical processes related to the transfer of heat and moisture • Explain change of state • Understand the background of formation of cloud and its classification. Presented by Mohd Amirul for AMC

5. Introduction • Moisture in atmosphere creates a variety of hazards. • Water can be solid, liquid, and gaseous states. • What is the difference between moisture and humidity? • Moisture: caused by water(usually can be seem) • Humidity: the amount of water vapor inside atmosphere. (usually can’t be seem) Presented by Mohd Amirul for AMC

6. Water Vapor Presented by Mohd Amirul for AMC

7. Water Vapor • Invisible • Can be measured in TWO ways: • Relative Humidity • Dew Points Presented by Mohd Amirul for AMC

8. i. Relative Humidity • Express in percent • Relative humidity: express the degree of saturation. • 100% - Saturated. • Below 100% - unsaturated. • ‘Relative’ means relates the actual water vapor present that which could be present. • E.g. 50% humidity means the air could hold twice as much water vapor as it actually present. Presented by Mohd Amirul for AMC

9. Cont. • In fact, warm air can hold more water than cool air. • Temperature determine the maximum amount of water vapor air can hold • Temperature increase, water vapor increase, relative humidity decrease. • When air is cooled, can’t hold more water vapor (water becomes liquid/solid) • Condensation/sublimation begins to occur - SATURATED (100% Rel. Humidity) Presented by Mohd Amirul for AMC

10. Cont. Presented by Mohd Amirul for AMC

11. ii. Dew Points • Dew Points: Temperature to which air must be cooledto become saturated by the water vapor already present in the air. (Temperature at which water vapor becomes saturated and condensation begins.) Presented by Mohd Amirul for AMC

12. Cont. Presented by Mohd Amirul for AMC

13. Cont. • Temperature-dew point spread. • Aviation weather reports normally include air temperature and dew point temperature. • Temperature-dew point spread: difference between temperature and dew point. • As SPREAD less, relative humidity increase. • Spread will be 100% when temperature and dew point are same. Presented by Mohd Amirul for AMC

14. Cont. • Has a little bearing about precipitation but important in anticipating (predicting) fog. *saturate: cause chemical compound, vapour, solution to unite with the greatest amount of another substance. Presented by Mohd Amirul for AMC

15. Change of State Presented by Mohd Amirul for AMC

16. Change of State • Change of State: a change from one state (solid or liquid or gas) to another without a change in chemical composition. Presented by Mohd Amirul for AMC

17. Cont. • Involving: • Evaporation: The process of becomes a vapor from liquid. • Condensation: The process of change from gas to liquid • Sublimation: The process of change directly from solid to gas or vice versa. • Freezing: The process of change from liquid to solid. • Melting: The process of change from solid to liquid. *Example of Sublimation: Snow/Ice crystals result from sublimation of water vapor directly to solid state. Presented by Mohd Amirul for AMC

18. Cont. Presented by Mohd Amirul for AMC

19. Cont. Latent Heat • Any change of state involves heat transaction. • Latent heat: Heat absorbed or radiated during a change of phase at a constant temperature and pressure • Gas have the high energy than solid. It can be prove by its rapid movement of molecules. Presented by Mohd Amirul for AMC

20. Cont. • Types of latent heat: • Latent heat of vaporization • Involves during evaporation and condensation process • The heat energy restored in the water vapor and release during condensation. • Latent heat of fusion • Involves when melting and freezing • Heat energy restored during melting and released during freezing. • Latent heat of sublimation: • Involve sublimation Presented by Mohd Amirul for AMC

21. Cont. Presented by Mohd Amirul for AMC

22. Condensation Nuclei • As air become saturated water vapor begins to condensed (water vapor decrease) on the nearest available surface. • What surface in the atmosphere on which water vapor may condense?? Presented by Mohd Amirul for AMC

23. Cont. • Surface in the atmosphere on which water vapor may condense Condensation Surface. • Condensation Surface: the surface where abundance microscopic solid particles suspended in the air. • Theses microscopic solid particles we call as CONDENSATION NUCLEI • E.g. salt, dust, combustion by product. Presented by Mohd Amirul for AMC

24. Cont. • As the water vapor condense or sublimates on condensation nuclei, liquid or ice particles begin to grow. • The particle ice or liquid doesn’t depend entirely on temperature • E.g.: Liquid Water may be present at temperature well below freezing. Presented by Mohd Amirul for AMC

25. Supercooled Water • Supercooled: Water droplet colder than 0˚C (liquid water below freezing point) • When these water droplets strike on expose objectthe impact induce FREEZING!! • May result aircraft icing. Presented by Mohd Amirul for AMC

26. Cont. Presented by Mohd Amirul for AMC

27. Cont. • Some of the supercooled water left in clouds at temperature between 0˚C to -15 ˚C • Amount of supercooled water become less. • At temperature colder than -15 ˚C sublimation commonly occur. • Sublimation will form ice crystals/clouds/fog. Presented by Mohd Amirul for AMC

28. Cont. • Strong vertical current may carry supercooled water to great height where temperature are much colder than -15 ˚C Presented by Mohd Amirul for AMC

29. Dew and Frost • Dew: water that has condensed on a cool surface overnight from water vapor in the air. • Formation of Dew: • During night (with wind or no wind), Flora (vegetation) cools by radiation (terrestrial radiation) to a temperature at or below the dew point of air. *moisture form on the leaves ambiguous to moisture form in warm room. Presented by Mohd Amirul for AMC

30. Cont. • Frost: The formation of ice on the surface. • Formation of Frost: • Form in much same way with dew. • The difference is dew point of surrounding air must be colder than freezing. In this case, water vapor sublimates directly as ice crystals frost rather than condensing as dew. Presented by Mohd Amirul for AMC

31. Cont. • But sometimes dew forms and later freezes Frozen Dew • However, frozen dew can easily be distinguish from frost. • Frozen dew is hard and transparent. • Frost is white and opaque. Presented by Mohd Amirul for AMC

32. Cont. • What is the difference between frost and snow? • Snow-can form/fall all day long • Frost-form in the cold of winter morning Presented by Mohd Amirul for AMC

33. Clouds Presented by Mohd Amirul for AMC

34. The Clouds • Clouds: A visible mass of water or ice particles suspended at a considerable altitude. (A visible manifestation of condensation or deposition in the atmosphere) • Clouds can indicate following problem: • Turbulence • Visibility • Precipitation • Icing Presented by Mohd Amirul for AMC

35. Cont. • Turbulence: Unstable flow of a liquid or gas in atmosphere. • Fog: ‘cloud’ on the ground. Presented by Mohd Amirul for AMC

36. Cont. • Cloud Base • The height of the lowest part of the cloud above the surface. • Similar to condensation surface/level. • Can be estimated using ceilometer. • Ceilometer: Laser beam pointing vertically and the receiver put at the same location. Presented by Mohd Amirul for AMC

37. Cloud Formation • Clouds are formed by air being lifted and cooled adiabatically (without heat transfer) until condensation occur. Presented by Mohd Amirul for AMC

38. Cont. • Remember back Condensation Nuclei • atmosphere contains particles that have an affinity for water ---These serve as centers for condensation. Cloud Condensation Nuclei (CCN) Presented by Mohd Amirul for AMC

39. The atmosphere has plenty of CCN Dust Salt Spray from Oceans Volcanoes Sulfate Particles from Phytoplankton Forest Fires Trees Anthropogenic Origins Presented by Mohd Amirul for AMC

40. CCN are more plentiful near the surface of the earth. • CCN are more plentiful over land rather than the ocean. • The formation of cloud droplets using CCN is called: Heterogeneous Nucleation. Presented by Mohd Amirul for AMC

41. Cont. • The air must become saturated for condensation/sublimation to occur. • Saturation can result from • cooling temperature, • increasing dew point • or both Presented by Mohd Amirul for AMC

42. Cont. • But the cooling is more predominant (frequent) for the air to become saturated. • Cooling Process: • 3 basics processmay cool the air to saturation: • Air moving over a colder surface • Stagnant air overlying a cooling surface • Expansion cooling in upward moving air Presented by Mohd Amirul for AMC

43. Cont. • Expansion cooling is a major cause of cloud formation. Presented by Mohd Amirul for AMC

44. Cloud Classification • Clouds are classify as follows: • Heap Clouds • Layer Clouds Presented by Mohd Amirul for AMC

45. Cont. a. Heap Clouds • General Characteristics: • Unstable • Isolated with large vertical and small horizontal extent. • Associated with changeable weathers, showers, thunderstorm and turbulence. Presented by Mohd Amirul for AMC

46. Cont. • 3 main types: • Cumulus (Cu) • Comulonimbus (Cb) • Altocumulus Castellanus (Acc) Presented by Mohd Amirul for AMC

47. Cont. i. Cumulus (Cu) • Characteristic: • Give heavy showers and moderate to heavy clear ice and turbulence. • Brilliant (striking) white to grey, denseisolated clouds. • Clumped or heaped shapes. • Field of Cu often have bases all at same (Condensation Surface) level • Instability cloud at cold front. • *Cold Front: zone where cold air replaces warm air Presented by Mohd Amirul for AMC

48. Cont. ii. Comulonimbus (Cb) • Characteristics: • Thunderstorm Clouds • Severe turbulence and heavy clear icing., heavy showers, hail, thunderstorm and lightning. • Occur at cold front and major tropical storms • Huge towering cloud, dark base and white sides. Presented by Mohd Amirul for AMC

49. Cont. iii. Altocumulus (Acc) • Characteristics: • Warning of unstable air and thunderstormswithin 24 hours. • white or grey, broken cumulus-like clouds; • Sometimes arranged in lines. Presented by Mohd Amirul for AMC

50. Cont. b. Layer Clouds • General Characteristics: • Occur in stable condition • Sheets of cloud cover a wide area • The weather can be dull (darkened with overcast(cover by cloud)) for lengthy periods with continuous light to moderate precipitation. Presented by Mohd Amirul for AMC