Transcript Precipitation

Visualizing Physical Geography
by Alan Strahler and Zeeya Merali
Chapter 4
Atmospheric Moisture and Precipitation
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
Visualizing Physical Geography
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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
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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
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Water and the Hydrosphere
Three States of Water:
•Solid (ice)
•Liquid (water)
•Gas (vapor)
Visualizing Physical Geography
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Water and the Hydrosphere
Hydrosphere: Total realm of water at
Earth’s surface.
•Oceans
•Ice
•Surface water
•Groundwater
•Atmospheric water
•Soil moisture
•Biota
Visualizing Physical Geography
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Water and the Hydrosphere
Distribution of water in the
hydrosphere
• Oceans: 97.5%
• Fresh water: 2.5%
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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
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Water and the Hydrosphere
Precipitation: Particles of
liquid water or ice that fall
from the atmosphere and
may reach the ground.
Visualizing Physical Geography
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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
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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
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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
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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
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Humidity
Dew-point temperature:
temperature at which air
with a given humidity will
reach saturation when
cooled without changing its
pressure
Visualizing Physical Geography
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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
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The Adiabatic Process
Atmospheric pressure decreases with altitude
so...
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
Visualizing Physical Geography
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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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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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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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Clouds
Cloud Families: High clouds, middle clouds, low
clouds, clouds of vertical development
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Clouds
Cumulus Clouds
Cumuliform clouds: globular masses of cloud,
associated with parcels of rising air
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Clouds
Stratus Clouds
Image ID: wea02050, NOAA's National Weather Service (NWS) Collection
Photographer: Ralph F. Kresge
http://www.photolib.noaa.gov/htmls/wea02050.htm
Stratiform clouds: blanket-like, cover large areas
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Clouds
Cirrus Clouds
Cirrus clouds: high, thin, wispy clouds composed
of ice crystals
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Clouds
Fog is a cloud layer at or close to Earth’s surface
• 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”)
Image ID: wea03250, NOAA's National Weather Service (NWS) Collection
Photographer: LCDR Mark Wetzler, NOAA Corps
http://www.photolib.noaa.gov/htmls/wea03250.htm
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Precipitation
Types of Precipitation
• Rain
• Snow
• Hail
• Ice storm
Rain formation in warm clouds
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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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Precipitation
Orographic precipitation: precipitation induced when moist
air is forced over a mountain barrier
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Precipitation
Rain shadow: a belt of dry climate that extends down
and beyond the leeward slope of a mountain range
Visualizing Physical Geography
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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
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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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Precipitation
Thunderstorm Cell
Hailstorm Frequency
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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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Air Quality
Acid deposition: sulfur dioxide (SO2) and nitric oxide
(NO2) 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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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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Air Quality
Air pollution control:
• Improve controls on industrial
emissions
• Develop alternative, nonpolluting technologies
•Solar
•Wind
•Geothermal
• Reduce fossil fuel consumption
Visualizing Physical Geography
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