The document discusses several key physical properties of water and the water cycle: 1) Water has a unique molecular structure that allows it to exist in solid, liquid, and gas forms on Earth. It takes a significant amount of energy to change between these phases due to hydrogen bonding between molecules. 2) The vapor pressure of water increases with temperature, as warmer air can hold more water vapor. When air reaches saturation, the rate that molecules enter and leave liquid water is equal. 3) Relative humidity compares the actual vapor pressure to the saturation vapor pressure, ranging from 0-100%. Dew point temperature indicates the water content of air.

1. Properties of Water Physical States only natural substance that occurs naturally in three states on the earth’s surface Heat Capacity Highest of all common solids and liquids Surface Tension Highest of all common liquids Latent Heat of Fusion Highest of all common substances Compressibility Virtually incompressible as a liquid Density Density of seawater is controlled by temperature, salinity and pressure Liquid has maximum density at +4 o C; solid phase has lower density!

2. Properties of Water (cont’) Radiative Properties transparent to visible wavelengths virtually opaque to many infrared wavelengths large range of albedo possible water 10 % (daily average) Ice 30 to 40% Snow 20 to 95% Cloud 30 to 90%

3. Molecular Structure of Water Water's unique molecular structure and hydrogen bonds enable all 3 phases to exist in earth's atmosphere. Sublimation & deposition describe the non-incremental changes between solid and vapor phases. water molecule ice

4. Energy associated with phase change Sublimation Deposition

5. Why does it take so much energy to evaporate water? In the liquid state, adjacent water molecules attract one another “ -” charge on O attracted to “+” charge on H we call this hydrogen bonding This same hydrogen bond accounts for surface tension on a free water surface column of water “sticks together”

6. Sublimation – evaporate ice directly to water vapor Take one gram of ice at zero degrees centigrade Energy required to change the phase of one gram of ice to vapor: Add 80 calories to melt the ice Add 100 calories to raise the temperature to 100 degrees C Add 540 calories to evaporate the liquid Total Energy ADDED for sublimation of 1 gram of ice: 80 + 100 + 540 = 720 calories

7. Deposition – convert vapor directly to ice Take one gram of water vapor at 100 degrees Centigrade Release 540 calories to condense Release 100 calories to cool temperature of liquid to o C Release 80 calories to freeze water Total energy RELEASED for deposition of 1 gram of ice 540 + 100 + 80 = 720 calories

8. Water vapor pressure Molecules in an air parcel all contribute to pressure Each subset of molecules (e.g., N 2 , O 2 , H 2 O) exerts a partial pressure The VAPOR PRESSURE , e , is the pressure exerted by water vapor molecules in the air similar to atmospheric pressure, but due only to the water vapor molecules often expressed in mbar (2-30 mbar common at surface)

9. Water vapor saturation Water molecules move between the liquid and gas phases When the rate of water molecules entering the liquid equals the rate leaving the liquid, we have equilibrium The air is said to be saturated with water vapor at this point Equilibrium does not mean no exchange occurs

10. Relationship between e S and T The saturation vapor pressure of water increases with temperature At higher T, faster water molecules in liquid escape more frequently causing equilibrium water vapor concentration to rise We sometimes say “ warmer air can hold more water ” There is also a vapor pressure of water over an ice surface The saturation vapor pressure above solid ice is less than above liquid water

11. e S vs T schematic Saturation vapor pressure depends upon temperature

12. How do we express the amount of water vapor in an air parcel? Absolute humidity mass of water vapor/volume of air (g/m 3 ) changes when air parcel volume changes Specific humidity mass of water vapor/mass of air (g/kg) Mixing ratio mass of water vapor/mass of dry air (g/kg) Specific humidity and mixing ratio remain constant as long as water vapor is not added/removed to/from air parcel Dew point temperature

13. Expressing the water vapor pressure Relative Humidity (RH) is ratio of actual vapor pressure to saturation vapor pressure 100 * e/e S Range: 0-100% (+) Air with RH > 100% is supersaturated RH can be changed by Changes in water vapor content, e Changes in temperature , which alter e S

14. Dewpoint Temperatures Dewpoint is a measure of the water vapor content of the air It is not a measure of temperature !

15. Which environment has higher water vapor content?

16. Why is the southwest coast of the US hot and dry while the Gulf coast is hot and moist? Both are adjacent to large bodies of water Both experience onshore wind flow on a regular basis Why does one have a desert like climate and the other ample moisture and rainfall?

17. Humidity reflects water temps The cold water temperatures typically found off the west coast of continents are a result of oceanic upwelling which ocean currents typically cause in these locations

18. Water vapor is distributed throughout the atmosphere Generally largest amounts are found close to the surface, decreasing aloft Closest to the source - evaporation from ground, plants, lakes and ocean Warmer air can hold more water vapor than colder air

21. Take-Away Points Weather is driven by unequal solar heating and cooling Air motions are affected by the Coriolis Effect and “centrifugal” force High and Low Pressure Systems Air flows parallel to pressure contours (Geostrophic winds) Air masses meet along sharp boundaries or fronts Weather is inherently chaotic and that limits our ability to forecast it

22. The Seasons

23. Uneven solar heating on Earth Solar energy in high latitudes: Has a larger “footprint” Is reflected to a greater extent Passes through more atmosphere Is less than that received in low latitudes

24. Earth’s seasons Earth’s axis is tilted 23½ º from vertical Northern and Southern Hemispheres are alternately tilted toward and away from the Sun Causes longer days and more intense solar radiation during summer

25. Oceanic heat flow A net heat gain is experienced in low latitudes A net heat loss is experienced in high latitudes Heat gain and loss are balanced by oceanic and atmospheric circulation

26. Physical properties of the atmosphere: Composition (dry air) Percent Gas Trace All others 0.036% Carbon dioxide (CO 2 ) 0.9% Argon (Ar) 20.9% Oxygen (O 2 ) 78.1% Nitrogen (N 2 )

27. Physical properties of the atmosphere: Temperature Troposphere is: Lowermost part of the atmosphere Where most weather occurs Temperature of troposphere cools with increasing altitude

28. Physical properties of the atmosphere: Density Warm, low density air rises Cool, high density air sinks Creates circular- moving loop of air (convection cell)

29. Physical properties of the atmosphere: Water vapor Cool air cannot hold much water vapor, so is typically dry Warm air can hold more water vapor, so is typically moist Water vapor decreases the density of air

30. Physical properties of the atmosphere: Pressure A column of cool, dense air causes high pressure at the surface, which will lead to sinking air A column of warm, less dense air causes low pressure at the surface, which will lead to rising air

31. Physical properties of the atmosphere: Movement Air always moves from high-pressure regions toward low-pressure regions Moving air is called wind

32. The Coriolis effect The Coriolis effect Is a result of Earth’s rotation Causes moving objects to follow curved paths: In Northern Hemisphere, curvature is to right In Southern Hemisphere, curvature is to left Changes with latitude: No Coriolis effect at Equator Maximum Coriolis effect at poles

33. A merry-go-round as an example of the Coriolis effect To an observer above the merry-go-round, objects travel straight To an observer on the merry-go-round, objects follow curved paths

34. The Coriolis effect on Earth As Earth rotates, different latitudes travel at different speeds The change in speed with latitude causes the Coriolis effect Figure 6-9a

35. Missile paths demonstrate the Coriolis effect Two missiles are fired toward a target in the Northern Hemisphere Both missiles curve to the right Figure 6-9b

36. Wind belts of the world Figure 6-10

37. Characteristics of wind belts and boundaries Polar high pressure Polar easterlies Polar front Prevailing westerlies Horse latitudes Trade winds Doldrums Wind belt or boundary name High press. boundary Polar (90 º) Cool easterly winds 60-90 º Low press. boundary 60 º Mid-latitude winds 30-60 º High press. boundary 30 º Persistent easterlies 5-30 º Low press. boundary Equatorial (0-5 º) Characteristic Region/Latitude

38. Coriolis effect influences air movement Northern Hemisphere winds curve to the right as they move from high to low pressure Causes wind to circulate: Clockwise around high-pressure regions Counterclockwise around low-pressure regions

39. Air masses that affect U.S. weather

40. Origin and paths of tropical cyclones Tropical cyclones are intense low pressure storms created by: Warm water Moist air Coriolis effect Includes: Hurricanes Cyclones Typhoons

41. Hurricane occurrence Hurricanes have wind speeds of at least 120 kilometers (74 miles) per hour Worldwide, about 100 storms grow to hurricane status each year In the Northern Hemisphere, h urricane season is generally between June 1 and November 30

42. Hurricane structure Hurricanes have: Circular cloud bands that produce torrential rain The ability to move into the mid-latitudes A central eye

43. Hurricanes produce storm surge Storm surge: Is a rise in sea level created by hurricane coming ashore Can be up to 12 meters (40 feet) high Causes most destruction and fatalities associated with hurricanes

44. Climate regions of the ocean

45. How a greenhouse works Sunlight passes through the clear covering of a greenhouse It converts to longer wavelength heat energy Heat cannot pass through the covering and is trapped inside

46. The heating of Earth’s atmosphere

47. Anthropogenic gases that contribute to the greenhouse effect 8% CFC-12 4% CFC-11 8% Tropospheric ozone (O 3 ) 5% Nitrous oxide (N 2 O) 15% Methane (CH 4 ) 60% Carbon dioxide (CO 2 ) Relative contribution Greenhouse Gas

48. Carbon dioxide is increasing in the atmosphere As a result of human activities, carbon dioxide in the atmosphere has increased by 30% since 200 years ago

49. Earth’s average temperature is rising Earth’s average surface temperature has risen at least 0.6°C (1.1°F) in the last 130 years May be related to increase in atmospheric carbon dioxide

50. Predicted changes with increased greenhouse warming Higher than normal sea surface temperatures that could affect world climate More severe droughts or increased precipitation Water contamination and outbreaks of water-borne diseases Longer and more intense heat waves Shifts in the distribution of plants and animals Potential melting or enlargement of polar ice caps

51. Atmospheric Circulation 1. Weather is driven by unequal solar heating and cooling

52. Atmospheric Circulation 1. Weather is driven by unequal solar heating and cooling

53. Asymmetric Earth 1. Weather is driven by unequal solar heating and cooling

54. Asymmetric Earth 1. Weather is driven by unequal solar heating and cooling

55. Atmospheric Circulation 1. Weather is driven by unequal solar heating and cooling

56. Zonal and Meridional Flow 1. Weather is driven by unequal solar heating and cooling

57. Semi-Permanent Features, January 1. Weather is driven by unequal solar heating and cooling

58. Semi-Permanent Features, July 1. Weather is driven by unequal solar heating and cooling

59. Rotation Effects 2. Air motions are affected by the Coriolis Effect and “centrifugal” force

60. The Coriolis Effect Due to moving on a rotating earth Things on equator are moving faster than points near poles Affects: Winds Ocean Currents Tides 2. Air motions are affected by the Coriolis Effect and “centrifugal” force

61. The Coriolis Effect Things moving toward the equator are deflected west Things moving poleward are deflected east Deflected to Right in Northern Hemisphere Deflected to Left in Southern Hemisphere 2. Air motions are affected by the Coriolis Effect and “centrifugal” force

62. The Coriolis Effect 2. Air motions are affected by the Coriolis Effect and “centrifugal” force

63. The Coriolis Effect 2. Air motions are affected by the Coriolis Effect and “centrifugal” force

64. The Coriolis Effect 2. Air motions are affected by the Coriolis Effect and “centrifugal” force

65. “Centrifugal” Force Does Not Exist When anything turns, the only forces that act are in the direction of the turn These forces are called centripetal (center-seeking) force “Centrifugal” force is an illusion “Centrifugal” force is due to inertia and centripetal force opposing each other 2. Air motions are affected by the Coriolis Effect and “centrifugal” force

66. High Pressure Systems 3. High and Low Pressure Systems

67. High Pressure Systems Air flows out from center Spin clockwise in Northern Hemisphere No air mixing Stable, fair weather Sinking Air, few clouds Long duration can result in inversions, pollution Winter: often extreme cold Cold Air is Dense Clear Skies and Radiational Cooling 3. High and Low Pressure Systems

68. Low Pressure Systems 3. High and Low Pressure Systems

69. Why Counterclockwise? 3. High and Low Pressure Systems

70. Low Pressure Systems Air flows in toward center Spin counter-clockwise in Northern Hemisphere Mixes air of different properties Associated with fronts Stormy, sometimes violent weather Passage often results in sharp change in weather conditions 3. High and Low Pressure Systems

71. Geostrophic Winds As air flows in or out of pressure cells, Coriolis Effect deflects it At surface, friction limits the deflection. Winds blow about 45 degree angles to isobars Aloft, friction not a factor Deflection continues until limited by pressure gradient (winds can’t go against pressure) Winds blow parallel to contours This is called geostrophic flow

72. Geostrophic Flow

73. Geostrophic Flow

74. Geostrophic Flow 4. Air flows parallel to pressure contours (Geostrophic winds)

75. 1905 Weather Map of US

76. First U.S. Weather Map With Fronts

77. Fronts and Low Pressure Systems 5. Air masses meet along sharp boundaries or fronts

78. Fronts 5. Air masses meet along sharp boundaries or fronts

79. Warm Fronts 5. Air masses meet along sharp boundaries or fronts

80. Warm Fronts Gradual Onset Warm Air over Cool Air Little Turbulence Weather Rarely Violent 5. Air masses meet along sharp boundaries or fronts

81. Cold Fronts 5. Air masses meet along sharp boundaries or fronts

82. Cold Fronts Abrupt Onset Cold Air Lifting Warm Air Considerable Turbulence Weather Sometimes Violent Thunderstorms Common Can Spawn Tornadoes 5. Air masses meet along sharp boundaries or fronts

83. Old Low Pressure Systems 5. Air masses meet along sharp boundaries or fronts

84. Occluded Fronts 5. Air masses meet along sharp boundaries or fronts

85. Occluded Fronts Two fronts merge Any two types of front can occlude Most common: Cold Front overtakes Warm Front Starts off like a warm front, finishes like a cold front 5. Air masses meet along sharp boundaries or fronts

86. Weather Prediction 5. Air masses meet along sharp boundaries or fronts

87. Weather Prediction 5. Air masses meet along sharp boundaries or fronts

88. Weather Prediction 5. Air masses meet along sharp boundaries or fronts

89. Chaos x

90. Chaos Theory Does Not Mean: Cloned Dinosaurs will run amok Systems do not follow physical laws Systems behave with wild unpredictability Systems do not have limits Phenomena cannot be predicted 6. Weather is inherently chaotic and that limits our ability to forecast it

91. Chaos Theory Does Mean: Small differences compound over time There are limits to how accurately phenomena can be predicted Examples: Weather The Planets Traffic 6. Weather is inherently chaotic and that limits our ability to forecast it

93. Who Cares About Water Anyways? Phase changes of water important for energy transport in atmosphere Clouds! Precipitation!

94. Overview Cloud: Collection of liquid water drops or ice crystals Clouds form as 1) Water vapor condenses onto small particles known as condensation nuclei to form liquid water drops, or 2) Water vapor deposits onto small particles known as ice nuclei that allow for ice crystal formation In a cloud, water can be present in all three phases at the same time

95. Hydrologic Cycle Global precipitation = Global evaporation

96. Terms Evaporation: liquid water molecules break bonds with other molecules to escape to gaseous phase Condensation: Water vapor returns to liquid state Sublimation: Ice changes directly to water vapor Deposition: Water vapor changes directly to ice Transpiration: Plants releasing water vapor into air

97. Temperature and Evaporation Evaporation occurs when liquid water molecules gain enough kinetic energy to break bonds The higher the temperature of water, the higher the kinetic energy of its molecules, thus the higher the evaporation rate Evaporation is a cooling process

98. Balance of Evaporation & Condensation Net Condensation: Condensation exceeds evaporation Net Evaporation: Evaporation exceeds condensation Vapor Pressure: Water vapor’s contribution to total pressure

100. Equilibrium Vapor Pressure & Temperature

101. Birth of Clouds Relative Humidity: ( vapor pressure / equilibrium vapor pressure) * 100 At saturation (rate of condensation = rate of evaporation), RH = 100% Clouds form when RH exceeds 100% by a few tenths of a percent Water vapor condenses onto CCN…some hygroscopic, meaning they attract water vapor In summer, when RH exceeds 80%, net condensation occurs on some particles (pollution), leading to haze…associated with poor air quality

103. Mechanisms to induce cloud formation For clouds to form, there must be net condensation We can get this by cooling the air As temperature lowers, molecular speeds decrease, and water vapor gathers near CCN The amount of cooling needed is inversely proportional to the amount of water vapor in the air

104. Fog Formation by Cooling Air

105. Cooling via lifting Air pressure (density) decreases with height Rising air parcels expand, cooling as they do work on environment If vapor pressure = equilibrium vapor pressure => condensation

106. Clouds due to Lifting

107. Orographic Lifting: Lifting by Terrain Windward side of mountain, facing prevailing wind, is extremely wet Leeward side, sheltered from wind, very dry…known as rain shadow

108. Clouds due to Terrain

109. Orographic Lifting: California

110. Mixing Warm & Cold Air Masses

111. Assessing Air’s Moisture Content Problems with RH because denominator depends on temperature Cold, dry air masses can have a high RH, even if they hold little water vapor Relative humidity varies with time of day

112. Dew Point: Absolute measure of water vapor Dew Point: Temperature air must be cooled (at constant pressure) to reach saturation Less than or equal to temperature Higher the dew point, more water vapor in air Frost point if air temperature below 32ºF Measured with a hygrometer or sling psychrometer Changes by evaporating water into air, mixing drier air from above, wind blowing in moist or dry air from another region (air dries behind cold front, moistens before cold front)

113. Applying Dew Point to Weather Forecasting 1) Cloud Base Height Temperature of rising air decreases faster than dew point…has a decent chance of eventually reaching dew point 2) First-Guess Low Temperature 3) Severe Weather High dew points indicate enhanced risk

114. The Earth’s Hydrologic Cycle