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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Chapter 4 Atmospheric Moisture and Precipitation Visualizing Physical Geography by Alan Strahler and Zeeya Merali
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Chapter Overview Water and the Hydrosphere Humidity The Adiabatic Process Clouds Precipitation Air Quality
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Objectives Describe how water changes state and interacts in the hydrosphere. Define and explain humidity. Explain the adiabatic process in relationship to cloud formation. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
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Objectives Describe cloud classification and fog. Describe precipitation in its various forms. Describe and explain air pollutants and the damage they can do. Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.
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Water and the Hydrosphere Three States of Water: Solid (ice) Liquid (water) Gas (vapor)
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Hydrosphere: Total realm of water at Earth’s surface. Oceans Ice Surface water Groundwater Atmospheric water Soil moisture Biota Water and the Hydrosphere
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Water and the Hydrosphere Distribution of water in the hydrosphere Oceans: 97.5% Fresh water: 2.5%
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Water and the Hydrosphere Hydrologic Cycle: Water moves among the ocean, atmosphere and land Evaporation Precipitation Transpiration from plants Runoff Sinks into soil Recharge of groundwater
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Precipitation: Particles of liquid water or ice that fall from the atmosphere and may reach the ground. Water and the Hydrosphere
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Humidity Humidity: the amount of water vapor in the air The maximum quantity of moisture that can be held in the air depends on air temperature
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Humidity Relative Humidity: compares the amount of water vapor present in the air to the maximum amount that the air can hold at that temperature Expressed as a percentage: At 100% relative humidity, air is saturated.
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Humidity Relative Humidity changes when: 1.Atmosphere gains or loses water vapor Evaporation 2.Temperature changes Lower temperature relative humidity rises Raise temperature relative humidity decreases
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Humidity Specific Humidity: actual quantity of water held by a parcel of air Grams of water vapor per kilogram of air (g/kg) Highest in equatorial zones Lowest near poles
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Dew-point temperature: temperature at which air with a given humidity will reach saturation when cooled without changing its pressure Humidity
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Adiabatic Process Adiabatic Principle: the physical principle that a gas cools as it expands and warms as it is compressed Change in temperature: caused only by a change in pressure not caused by heat flowing in or out of the gas
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Adiabatic Process As a parcel of air rises pressure on the parcel decreases air expands and cools As a parcel of air descends pressure on the parcel increases air is compressed and warms Atmospheric pressure decreases with altitude so...
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Adiabatic Process Dry adiabatic lapse rate: rate at which rising air is cooled by expansion when no condensation is occurring: 10º C per 1000 m (5.5 º F per 1000 feet)
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. The Adiabatic Process Wet adiabatic lapse rate: rate at which rising air is cooled by expansion when condensation is occurring: Ranges from 4-9º C per 1000 m (2.2-4.9º F per 1000 feet)
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Clouds Clouds consist of water droplets, ice crystals, or both Condensation nucleus: a tiny bit of solid matter (aerosol) in the atmosphere, on which water vapor condenses to form a tiny water droplet
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Clouds Cloud Families: High clouds, middle clouds, low clouds, clouds of vertical development
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Cumulus Clouds Cumuliform clouds: globular masses of cloud, associated with parcels of rising air Clouds
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Clouds Image ID: wea02050, NOAA's National Weather Service (NWS) Collection Photographer: Ralph F. Kresge http://www.photolib.noaa.gov/htmls/wea02050.htm Stratus Clouds Stratiform clouds: blanket-like, cover large areas
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Cirrus Clouds Cirrus clouds: high, thin, wispy clouds composed of ice crystals Clouds
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Clouds Image ID: wea03250, NOAA's National Weather Service (NWS) Collection Photographer: LCDR Mark Wetzler, NOAA Corps http://www.photolib.noaa.gov/htmls/wea03250.htm Radiation fog: formed when temperature of the air at ground level falls below dew point Advection fog: forms when warm moist air moves over a cold surface Common over oceans (“sea fog”) Fog is a cloud layer at or close to Earth’s surface
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Precipitation Rain formation in warm clouds Types of Precipitation Rain Snow Hail Ice storm
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Precipitation To form precipitation, air must move upward and chill by adiabatic processes. Four ways for air to move upward: 1.Orographic precipitation 2.Convectional precipitation 3.Cyclonic precipitation 4.Convergence
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Precipitation Orographic precipitation: precipitation induced when moist air is forced over a mountain barrier
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Precipitation Rain shadow: a belt of dry climate that extends down and beyond the leeward slope of a mountain range
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Precipitation Convectional precipitation: precipitation induced when warm, moist air is heated at the ground surface, rises, cools, and condenses to form water droplets, raindrops, and rainfall Lifting condensation level: level at which condensation begins
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Precipitation Thunderstorm: intense local storm associated with a tall, dense cumulonimbus cloud in which there are very strong updrafts of air Conditions: 1.Warm, moist air 2.An environmental lapse rate in which temperature decreases more rapidly with altitude than it does for either the dry or wet adiabatic lapse rates
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Precipitation Thunderstorm Cell Hailstorm Frequency
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Air Quality Air pollutant: an unwanted substance injected into the atmosphere from the Earth’s surface by either natural or human activities. Includes: Aerosols Gases Particulates Generated largely by combustion Smog (“smoke” + “fog”) contains nitrogen oxides, volatile organic compounds, ozone
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Air Quality Acid deposition: sulfur dioxide (SO 2 ) and nitric oxide (NO 2 ) released into the air combines with water to form sulfuric and nitric acids. May form: Acid rain Acid ice crystals Dry acid particles Acidity of rainwater in U.S., 2005
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Air Quality Effects of acid rain: Acid streams and lakes affect aquatic life Damage to forests Damage to soils Damage to buildings
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Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Air Quality Air pollution control: Improve controls on industrial emissions Develop alternative, non- polluting technologies Solar Wind Geothermal Reduce fossil fuel consumption
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