Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Lecture 7. Water and water vapor in the atmosphere 30 Sep 2010•Review of buoyancy, with an unusual demonstration of Archimedes principle.•Water is a polar molecule that forms hydrogen bonds. Consequently water is a structured liquid (and solid!). Water has a very high latent heat for evaporation and fusion, due to the forces between molecules associated with hydrogen bonds (2.5 x 106 J/kg). Ice is highly ordered, less dense than liquid water (very unusual), and has significant latent heat of fusion (0.34 x 106 J/kg). •Evaporation and condensation are dynamic processes always taking place at the liquid-air interface. The rate of evaporation increases with temperature. When the rate of evaporation equals the rate of condensation, the air and water are in equilibrium, and the air is said to be saturated with water vapor. The relationship between water vapor pressure and temperature is the Clausius-Clapeyron equation.Psat = A exp [B( 1/273.15 – 1/T)] B= 5308K. A=6.11 mbar=vapor press. 0C.•Vapor pressure increases sharply with temperature, due to the large latent heat. Water vapor content of air may be reported as partial pressure, relative humidity, dew point or frost point, or specific humidity. In general water vapor content is smaller than Psat, never significantly greater.•Discuss the observed distribution of temperature in the atmosphere.•When an air parcel moves up or down, its pressure changes according to the barometric law. Forces act on the parcel and change its size, meaning that work is done on/by the parcel. Work done on an air parcel by atmosphere, or by the parcel on the atmosphere, is related to change in the temperature of the air parcel.H O HH O H(—)++(—)One side of the water molecule has a negative electric charge, balanced by a positive charge on the other side. Water is a "polar" molecule.The positive side of each water molecule interacts strongly with the negative side of other water molecules. Water makes "hydrogen bonds", in ice, liquid, and vapor.A great deal of energy is needed to pull a water molecule out of the liquid, because of the strong hydrogen bonds. 2.26 × 106 J/kg needed to evaporate water. For comparison: 4.2 × 103 J/kg needed to raise the temperature of water by 1 K (1 C).The amount of energy needed to evaporate 1 kg of water is called the latent heat of vaporization.It is much larger for water than for most other liquids (due to hydrogen bonding).Evaporation and condensationMolecules are constantly evaporating from the surface of a liquid. Molecules in the gas above the liquid are constantly hitting the surface and condensing. The molecules that evaporate take energy from the liquid; the molecules that condense add energy.When a liquid is placed into a closed container, it will eventually reach a steady state where molecules evaporate from the surface and condense at exactly the same rate. Even though the molecules are constantly evaporating and condensing, there is no net transfer of molecules, or of energy.Lecture 7. Water and water vapor in the atmosphere•Review of buoyancy, with an unusual demonstration of Archimedes principle.•Water is a polar molecule that forms hydrogen bonds. Consequently water is a structured liquid (and solid!).•Evaporation and condensation are dynamic processes always taking place at the liquid-air interface. The rate of evaporation increases with temperature. •When the rate of evaporation equals the rate of condensation, the air and water are in equilibrium, and the air is said to be saturated with water vapor. The relationship between water vapor pressure and temperature is the Clausius-Clapeyron equation.•Water has a very high latent heat for evaporation and fusion, due to the forces between molecules associated with hydrogen bonds (2.5 x 106 J/kg). Thus the Clausius-Clapeyron equation shows a steep increase in vapor pressure with temperature:Psat = A exp [B( 1/273.15 – 1/T)] B= 5308K. A=6.11 mbar=water vapor press. at 0C.•Ice is highly ordered, less dense than liquid water (very unusual), and has significant latent heat of fusion (0.34 x 106 J/kg).•Water vapor content of air may be reported as partial pressure, relative humidity, dew point or frost point, or specific humidity. In general water vapor content is smaller than Psat, never greater.Vapor Pressure of WaterThe pressure of H2O vapor in equilibrium with liquid water.Clausius-Clapeyron relation. Water vapor pressure versus T.Psat = A exp [B( 1/273.15 – 1/T)] A=6.11 mbar, B= 5308K. A=water vapor pressure at 0C.6335 kJ required for latent heat of fusion2253 kJ required for latent heat of evaporation– 1kgLecture 7. Water and water vapor in the atmosphere•Review of buoyancy, with an unusual demonstration of Archimedes principle.•Water is a polar molecule that forms hydrogen bonds. Consequently water is a structured liquid (and solid!).•Evaporation and condensation are dynamic processes always taking place at the liquid-air interface. The rate of evaporation increases with temperature. •When the rate of evaporation equals the rate of condensation, the air and water are in equilibrium, and the air is said to be saturated with water vapor. The relationship between water vapor pressure and temperature is the Clausius-Clapeyron equation.•Water has a very high latent heat for evaporation and fusion, due to the forces between molecules associated with hydrogen bonds (2.5 x 106 J/kg). Thus the Clausius-Clapeyron equation shows a steep increase in vapor pressure with temperature:Psat = A exp [B( 1/273.15 – 1/T)] B= 5308K. A=6.11 mbar=water vapor press. at 0C.•Ice is highly ordered, less dense than liquid water (very unusual), and has significant latent heat of fusion (0.34 x 106 J/kg).•Water vapor content of air may be reported as partial pressure, relative humidity, dew point or frost point, or specific humidity. In general water vapor content is smaller than Psat, never greater.Vapor pressures of water and ice at atmospheric temperatures.Measuring the water vapor content of the atmosphere.Relative humidity—air has a given amount of water vapor (partial pressure P, mb). In general it will have less water vapor than in equilibrium with liquid at the same