Atmospheric Moisture and Precipitation

11. Humidity Facts Humidity is the amount of water vapor in the atmosphere Warm air can hold much more than cold air Cold dry air can have close to 0% Warm tropical air may have 4-5% Two ways to describe humidity (specific humidity and relative humidity)

12. Specific Humidity the actual quantity of water vapor in the air expressed as grams of water per kilogram of air (g/kg) used to describe the water content of large air masses, and how it varies by latitude

13. Relative Humidity and Air Temperature

14. Relative Humidity a measure of the amount of water vapor present in air relative to the maximum amount that the air can hold at a given temperature (%) e.g. if relative humidity is 50%, then it contains 1/2 the amount of water vapour it could hold at a given temperature relative humidity decreases as temperature increases

15. Relative Humidity and Temperature if no water vapour is added or removed from the air mass, then relative humidity decreases as temperature increases

16. Saturation vsAir Temperature

17. Dew Point Temperature as air is cooled it eventually becomes saturated (100% relative humidity) the temperature of saturation is called the dew point temperature if cooling continues, condensation begins and dew forms

18. After Saturation Occurs the AirMust Release Extra Water as Fluid

19. Saturation and Dew Point

20. Adiabatic Cooling and Heating

21. The Adiabatic Process when a gas expands, its volume increases and its pressure and temperature decrease air temperature change solely as a result of air expansion or contraction is a result of the adiabatic process the adiabatic lapse rate is used to quantify how the temperature of air decreases as it rises or increases as it ascends lapse rates differ for dry (unsaturated) and wet (saturated) air masses

22. Dry Adiabatic Lapse Rate Dry Adiabatic Lapse Rate (DALR) - decrease in temperature with altitude: 10�C/1000m

23. Wet (Saturated) Adiabatic Lapse Rate ranges from 4 to 9 degrees C per 1000 meters varies because it depends on temperature, pressure and water vapour content less than the DALR because as water condenses it releases latent heat, so the temperature decrease is less

24. Wet Adiabatic Lapse Rate as a parcel of air rises, it cools and becomes saturated at the dew point dew point lapse rate (1.8 degrees per 1000 meters) means that the dew point of the air parcel decreases as the air rises when it reaches its dew point, condensation occurs (lifting condensation level)

25. Clouds Made up of water droplets and/or ice particles form when air is saturated AND contains particles (condensation nuclei) e.g. dust, salts water can remain in liquid state below freezing (supercooled) to as low as -12�C (10�F)

26. high (eg. cirrus) middle (eg. altocumulus) low (eg stratus, cumulus)

27. Cumulus

28. Cumulonimbus Family D (Vertically developed)

29. Stratus

30. Nimbostratus

31. Stratocumulus

32. Altocumulus Altocumulus (Alto, "high", cumulus, "heaped") is a cloud belonging to a class characterized by globular masses or rolls in layers or patches, the individual elements being larger and darker than those of cirrocumulus and smaller than those of stratocumulus. Like other cumulus clouds, altocumulus signifies convection. It is usually white or gray, and often occurs in sheets or patches with wavy, rounded masses or rolls. Altocumulus often are seen preceding a cold front, and their presence on a warm, humid, summer morning frequently signals the development of thunderstorms later in the day.

33. Altostratus Altostratus is a cloud belonging to a class characterized by a generally uniform gray sheet or layer, lighter in color than nimbostratus and darker than cirrostratus. You can usually see the sun shining through them, and frequently cover the whole sky. Compare also with lower altitude stratus clouds. Altostratus is caused by a large air mass that is lifted then condensed, usually by an incoming frontal system and can be found over wide-spread areas. Altostratus clouds are potentially dangerous, because they can cause ice accretion on aircraft. Their altitude is from 6,500-20,000 feet. Made of ice crystals

34. Cirrus Cirrus clouds are characterized by thin, wisplike strands, often accompanied by tufts, leading to their common (non-standard) name of 'mare's tails'. Sometimes these brownish clouds are so extensive that they are virtually indistinguishable from one another, forming a veil or sheet called "cirrostratus". Sometimes convection at high altitudes produces another form of cirrus called "cirrocumulus", a pattern of small cloud tufts which include droplets of supercooled water. Cirrus usually form at altitudes above 8000 meters (26,000 feet).

35. Cirrocumulus A cirrocumulus is a high-altitude cloud, usually occurring at 20,000-40,000 ft (6,000-12,000 m). The term derives from the Latin cirrus "curl of hair", and cumulus "heaped". Like other cumulus clouds, cirrocumulus clouds signify convection. Unlike other cirrus clouds, cirrocumulus include liquid water droplets, although these are in a supercooled state. Ice crystals are also present, and typically, the ice crystals cause the supercooled water drops in the cloud to rapidly freeze, transforming the cirrocumulus into cirrostratus. This process can also produce precipitation in the form of a virga consisting of ice or snow. Thus cirrocumulus clouds are usually short-lived

36. Cirrostratus Cirrostratus clouds belong to a class characterized by a composition of dirt and dust and often by the production of halo phenomena. They appear as whitish and usually somewhat fibrous veils, often covering the whole sky and sometimes so thin as to be hardly discernible. Compare cirrostratus with other stratus cloud formations at lower altitude: altostratus, nimbostratus, and low altitude stratus clouds. Cirrostratus clouds are signs that precipitation will follow in the next 12-24 hours. These clouds are located above 6,000m (20,000ft).

37. Fog cloud layer at or close to the Earth�s surface radiation fog forms at night when air near the ground falls below the dew point temperature advection fog forms when warm moist air moves over a cool surface sea fog forms when cool marine air comes in contact with cold ocean currents

38. Fog (cloud on the earth�s surface)

39. Contrails

40. Just Weird Clouds

41. Just Weird Clouds

42. Just Weird Clouds

43. Precipitation Precipitation formation requires: growth of droplets in clouds ice crystal process - ice particles act as freezing nuclei coalescence process - large droplets collide with smaller ones and coalesce

44. produced in clouds well below the dew point temperature usually near cloud tops all precipitation begins as frozen water if it reaches the ground in liquid form - rain, drizzle (small drops) Precipitation

45. Types of Precipitation: freezing rain (ice crystals freeze onto a frozen surface) snow (ice crystals have not melted) sleet (ice crystals melt as they fall) hail (melting and refreezing crystals that form in thunder clouds)

56. Air Quality Air pollutants are undesirable gases, aerosols, and particulates injected into the atmosphere by human and natural causes

57. Smog and Acid Rain Smog is a kind of air pollution; the word "smog" is a portmanteau of smoke and fog. Classic smog results from large amounts of coal burning in an area and is caused by a mixture of smoke and sulfur dioxide

58. Smog and Acid Rain

59. Smog and Acid Rain Acid rain is rain or any other form of precipitation which is unusually acidic. It has harmful effects on plants, aquatic animals and buildings. Acid rain is mostly caused by human emissions of sulfur and nitrogen compounds which react in the atmosphere to produce acids. In recent years, many governments have introduced laws to reduce these emissions.

60. Smog and Acid Rain

61. Smog and Acid Rain

62. Smog and Acid Rain

63. Smog and Acid Rain