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Class #3: Humidity, condensation, and clouds Chapters 4 and 5 1Class #3 July 9, 2010.

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Presentation on theme: "Class #3: Humidity, condensation, and clouds Chapters 4 and 5 1Class #3 July 9, 2010."— Presentation transcript:

1 Class #3: Humidity, condensation, and clouds Chapters 4 and 5 1Class #3 July 9, 2010

2 Atmospheric Humidity Chapter 4 2Class #3 July 9, 2010

3 Circulation of Water in the Atmosphere A general definition of humidity is the amount of water vapor in the air. Remember, humidity is not constant through time or space, there is constant circulation of water through the hydrologic cycle. 3Class #3 July 9, 2010

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5 Stepped Art Fig. 4-1, p. 90 5Class #3 July 9, 2010

6 Fig. 4-2, p. 91 6Class #3 July 9, 2010

7 The Many Phases of Water Phase is related to molecular motion, an increase or decrease in motion creates a phase change. Ice is the coolest/slowest phase Water vapor is the warmest/fastest phase 7Class #3 July 9, 2010

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9 Evaporation, Condensation, & Saturation Evaporation is the change of liquid into a gas a requires heat. Condensation is the change of a gas into a liquid and releases heat. – Condensation nuclei Saturation is an equilibrium condition in which for each molecule that evaporates, one condenses. 9Class #3 July 9, 2010

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12 Humidity Any of a number of ways of specifying the amount of water vapor in the air. Absolute humidity: mass of water vapor/volume of air – Water vapor density – Not commonly used due to frequent change of volume 12Class #3 July 9, 2010

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15 Humidity Specific Humidity: mass of water vapor/mass of air Mixing ratio: mass of water vapor/mass of dry air Neither measurement changes with volume, must add or subtract water vapor. 15Class #3 July 9, 2010

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18 Humidity Vapor pressure: the pressure exerted by water vapor molecules in an air parcel (Daltons Law of Partial Pressure) – Fraction of total vapor pressure (1% or so) – More water molecules = high vapor pressure Saturation vapor pressure: the vapor pressure at which an air parcel will be saturated, changes with temperature 18Class #3 July 9, 2010

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20 Humidity Special Topic: Vapor Pressure & Boiling – Once water boils it requires more energy to increase temperature. – Water boils at a low temperature in the mountains and thus needs more energy and time to cook items as compared to sea level. 20Class #3 July 9, 2010

21 Humidity Relative Humidity: (actual water vapor/saturation water vapor)*100 – RH can be changed two ways: Change vapor content Change saturation – Decrease temperature causes an increase in relative humidity (inverse relationship). 21Class #3 July 9, 2010

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23 Humidity Relative Humidity and Dew Point – Dew point is the temperature at which saturation occurs – Cool air parcel to dew point and liquid water condenses – A good measure of actual water vapor content – Relative humidity indicates how close to saturation, dew point indicates the amount of water vapor 23Class #3 July 9, 2010

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25 Fig. 4-13, p Class #3 July 9, 2010

26 Fig. 4-13, p Class #3 July 9, 2010

27 Fig. 4-13, p Class #3 July 9, 2010

28 Fig. 4-13, p Class #3 July 9, 2010

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33 Fig. 4-15a, p Class #3 July 9, 2010

34 Fig. 4-15b, p Class #3 July 9, 2010

35 Humidity Relative Humidity in the Home – Due to an increase in temperature in a heated home there is a decrease in relative humidity, causing more evaporation from body, plants, etc Humidifier, chapped lips – Swamp cooler 35Class #3 July 9, 2010

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37 Humidity Relative humidity & human comfort – Its not the heat, its the humidity. – High relative humidity equates to less evaporative cooling. – Sweat cannot evaporate and cool the body – Wet bulb temperature – Heat Index 37Class #3 July 9, 2010

38 38Class #3 July 9, 2010

39 Humidity Special Topic: Heavier humid air – Due to the molecular weight of water as compared to nitrogen, humid air is lighter than dry air. – Baseball announcers are incorrect. 39Class #3 July 9, 2010

40 Humidity Measuring humidity – Sling psychrometer – Hygrometer 40Class #3 July 9, 2010

41 41Class #3 July 9, 2010

42 Condensation: DEW, Fog, & clouds Chapter 5 42Class #3 July 9, 2010

43 The Formation of Dew & Frost Dew forms on objects near the ground surface when they cool below the dew point temperature. – More likely on clear nights due to increased radiative cooling White frost forms when temperature cools below the dew point and the dew point is below 0°C 43Class #3 July 9, 2010

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46 Condensation Nuclei Particles suspended in the air that around which water condenses or freezes. – Hydrophobic/hygroscopic 46Class #3 July 9, 2010

47 Table 5-1, p Class #3 July 9, 2010

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50 Haze Dry condensation nuclei (above dew point) reflect and scatter sunlight creating blueish haze. Wet condensation nuclei (75% relative humidity) reflect and scatter sunlight creating grayish or white haze. 50Class #3 July 9, 2010

51 Fig. 5-4, p Class #3 July 9, 2010

52 Fog Saturation reached condensation forms a cloud near the ground Radiation fog: ground cools through conduction and radiation; ground fog – Valley fog created by cold air drainage – High inversion fog 52Class #3 July 9, 2010

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55 Fog Advection Fog: warm moist fog moves horizontally (advects) over a cool surface. – Summer fog on the Pacific coast Observation: Headlands – Air converges and rises over headlands forming fog as compared to lower elevation beaches. 55Class #3 July 9, 2010

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58 Fog Upslope Fog: moist air flows up an orographic barrier – East side of the Rockies Evaporation Fog: – Warm moist surface provides enough moisture to saturate a dry air parcel; short lived Steam fog Breath in winter 58Class #3 July 9, 2010

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61 Foggy Weather In general fog not common for most location in the US. However several areas do exist with a high frequency of fog. Two causes: – Elevation – Ocean currents 61Class #3 July 9, 2010

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63 Foggy Weather Environmental Issue: Fog dispersal – Mix air with air craft or fans – Introduce large particle into air to reduce total number of cloud droplets. – Use dry ice to lower temperature below freezing. 63Class #3 July 9, 2010

64 Clouds Classification of clouds: use Latin words to describe height and appearance. Factors described – Height: low, mid, high, vertical – Appearance: shape, density, color 64Class #3 July 9, 2010

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79 Some Unusual Clouds Not all clouds can be placed into the ten basic cloud forms. Unique atmospheric processes and environmental conditions create dramatic and exotic clouds. Unusual clouds and weather balloons often cause of UFO reports. 79Class #3 July 9, 2010

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82 Fig. 5-26, p Class #3 July 9, 2010

83 Fig. 5-27, p Class #3 July 9, 2010

84 Fig. 5-28, p Class #3 July 9, 2010

85 Fig. 5-29, p Class #3 July 9, 2010

86 Fig. 5-30, p Class #3 July 9, 2010

87 Fig. 5-31, p Class #3 July 9, 2010

88 Cloud Observations Sky conditions: cloud coverage divided into eighths and each amount associated with term such as scattered clouds. Observations: cloud ceilings – Ceilometer used at airports to determine height from clouds by light or laser striking clouds and then amount and speed of reflected light recorded. 88Class #3 July 9, 2010

89 Fig. 5, p Class #3 July 9, 2010

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91 Cloud Observations Satellite Observations – Geostationary, polar orbiting – Visible light provides a black and white picture of clouds – Infrared approximates cloud temperature which infers height – Satellites measure many other variables: sea surface temperatures, ozone, upper level features, snow cover, land cover 91Class #3 July 9, 2010

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