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

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

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.

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.

Water and the Hydrosphere Three States of Water: Solid (ice) Liquid (water) Gas (vapor)

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

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%

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

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

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

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.

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

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

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

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

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...

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)

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 ( º F per 1000 feet)

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

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Clouds Cloud Families: High clouds, middle clouds, low clouds, clouds of vertical development

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

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 Stratus Clouds Stratiform clouds: blanket-like, cover large areas

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Cirrus Clouds Cirrus clouds: high, thin, wispy clouds composed of ice crystals Clouds

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 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

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

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

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

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

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

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

Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc. Precipitation Thunderstorm Cell Hailstorm Frequency

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

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

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

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