Download Ch 22-Atmosphere

Ch 22-Atmosphere
• Objectives
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Composition of Earth’s atmosphere
Layers of atmosphere
Effects of air pollution
How radiant energy reaches Earth
How visible light and infrared energy warm Earth
Summarize the processes of radiation, conduction, and convection
Explain the Coriolis effect
Global patterns of air circulation, and name global wind belts
Identify factors that form local win patterns
Explain how heat energy affects the changing phases of water
Explain what absolute and relative humidity are, describe how they are
measured
Describe what happens when the temp of air decreases to the dew pt or
below the dew pt
Describe the conditions that are necessary for clouds to form
Explain the processes of cooling that can lead to formation of clouds
Identify the types of clouds
Describe ways in which fog can form
Processes that cause precipitation
Explain how rain can be produced artificially
Characteristics of Atmosphere
• Define atmosphere
– Mixture of gases that surrounds a planet
• Air-the atmosphere that is made up of a mixture of chemical
elements and compounds. What is the function of air?
• Composition of Atmosphere
– Most abundant elements=nitrogen, oxygen, argon
– Most abundant compounds in air=CO₂and H₂O
– Dust and pollen
• Water vapor-enters air as invisible gas
• Ozone in the Atmosphere
– Ozone-gas molecule that is made up of 3 oxygen atoms
– Why is ozone layer important?
– Chlorofluorocarbons-used in fridges and air conditioners-break
down ozone and cause layer to weaken
Atmospheric Pressure
• Atmospheric pressure=the force per unit area exerted on
a surface by weight of atmosphere
– Pressure is exerted equally in all directions
– Atmospheric pressure decreases as altitude increases
– Pressure changes as a result of differences in temp and in
amount of water vapor. Why?
• Measuring Atmospheric Pressure
– 3 units used for atmospheric pressure-atmospheres (atm),
millimeters or inches of mercury, and millibars
– Standard atmospheric pressure- 1 atm=760 mm of
mercury=1000 millibars
– Barometer-instrument used to measure atmospheric pressure
• Mercurial and aneroid barometers
Layers of Atmosphere
• What are the layers?
– Troposphere, Stratosphere, Mesosphere, Thermosphere
• Characteristics of Troposphere
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Closest to Earth
Nearly all the weather
Temp decreases w/ altitude
Average altitude of 12 km-varies w/ latitude and season
• Characteristics of Stratosphere
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Lies between Troposphere and Mesosphere
Ozone layer
Temp increases w/ altitude
Layer heated by absorption of solar radiation by ozone
Extends to about 50 km in altitude
• Characteristics of Mesosphere
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Lies bet Stratosphere and Thermosphere
Extends to about 80 km in altitude
Temp decreases as altitude increases
Avg temp of -90 deg C-coldest temp in
atmosphere
• Characteristics of Thermosphere
– Temp increases as altitude increases-Nitrogen
and oxygen atoms absorb solar radiation
– Extends from 80 to 400 km
– Ionosphere and exosphere
– Uppermost layer of atmosphere
• Concepts in Motion
Air Pollution
• What is the main source of pollution?
– Burning of fossil fuels, coal and petroleum
– Release sulfur dioxide gas, hydrocarbons,
nitrogen oxides, carbon monoxides, lead
• Smog-combination of smoke and fog
• Air cannot circulate up and away from
area
• How can air pollution be controlled?
Solar Energy and Radiation
• Radiation-all forms of energy that travel through space as
waves
– Visible light, ultraviolet light, x rays, radio waves
– Very high speed
• Electromagnetic waves-waves that make up all forms of
radiation
– Almost all forms of energy that reaches Earth
• Electromagnetic spectrum-all of the frequencies or
wavelengths of electromagnetic radiation
• Upper atmosphere-ultraviolet rays, x rays, gamma rays
absorbed here
• Lower atmosphere-visible and infrared waves absorbed here
• Scattering and reflection
– Albedo-is the fraction of solar radiation that is reflected off the
surface of an object
Absorption and Infrared Energy
• Radiation absorbed by rocks, soil, water
• Infrared rays and visible light heat surface
materials
• What is the greenhouse effect?
– Warming of the surface and lower atmosphere of
Earth that occurs when CO₂, water vapor, and other
gases in the air absorb and reradiate infrared
radiation
• What affects temperature of the atmosphere?
– Latitude, tilt of Earth’s axis, water vapor and CO₂,
wind patterns
Conduction and Convection
• Conduction-transfer of energy as heat
moves through a material
– Solid substances
– Heats only lowest few cm of atmosphere
• Convection-movement of matter due to
differences in density that are caused by
temperature variations
– Lower atmosphere heating occurs when
gases or liquids are heated unevenly
• Concepts in Motion
Atmospheric Circulation
• Coriolis Effect-curving of the path of a moving object
from an otherwise straight path due to Earth’s rotation
– Deflects moving objects along a path that depends on speed,
latitude, and direction of the object
– http://glencoe.com/sec/science/earthscience/2007/concept_moti
on/NGS/Visualizing_the_Coriolis_Effect_12.swf
• Global winds
– Trade winds-flow toward the equator between 30 and 0 deg. NE
and SE trade winds
– Westerlies-prevailing winds that blow throughout the contiguous
United States
– Polar Easterlies-about 60 deg latitude, zone of low pressure.
Winds blow from east to west bet 60-90 deg
– Doldrums and Horse latitudes- where trade wind systems meet
at equator, air movement is upward, surface winds are weak
– Jet streams-narrow band of strong winds that blow in the upper
troposphere
Local Winds
• Local conditions and local temps cause local
winds
• Breezes-gentle winds that extend over
distances of less than 100 km
• Land breeze-blows cool air from land to water
• Sea breeze-cool wind moving from water to
land. Forms in afternoon
• Mt breeze-at nighttime, cool air descends
from mt peaks
• Valley breeze-forms when warm air from
valleys moves upslope, during daylight hrs
Atmospheric Moisture
• What are the phases of water?
• How does water change?
– Heat energy is absorbed or released
• Latent heat-heat energy that is absorbed or released by
a substance during a phase change
• Condensation-water vapor changes back into a liquid,
energy is released to surrounding air, molecules move
closer together
• Evaporation-water molecules move so rapidly that they
collide and escape from liquid, form invisible water vapor
– Where does evaporation occur at most?
• Sublimation-solid changes directly into a gas
Humidity
• Water vapor in atmosphere
• What controls humidity?
– Condensation and evaporation
• Dew pt-the temp at which rate of condensation
equals rate of evaporation
• Absolute humidity-mass of water vapor
contained in a given volume of air
• Relative humidity-ratio of the actual water vapor
content of the air to the amount of water vapor
needed to reach saturation
Dew Point
• Air is warmer than objects near the
ground, air may cool to its dew point by
conduction when air is in contact w/ cold
surface
• Cool, clear nights, little wind
• Dew pt falls below freezing temp of water=
water vapor changes directly into solid ice
crystals or frost
Measuring Humidity
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Thin polymer film
Psychrometers
Dew cell
Hair hygrometer
Radiosonde
Why measure humidity?
Clouds and Fog
• Clouds-collections of small water droplets or ice crystals
that fall slowly through the air
• Form when condensation or crystallization occurs more
rapidly than evaporation or sublimation does
• Fog-a cloud that forms near or on Earth’s surface
• Cloud Formation
– Solid surface for condensation to take place
– Condensation nuclei-solid particle in the atmosphere that
provides surface on which water vapor condenses
– Rate of evaporation in equilibrium w/ rate of condensation, air
becomes saturated w/ water vapor
– Temp drops, condensation occurs more rapidly than evaporation
does
• Adiabatic Cooling-temp of an air mass
decreases as the air mass rises and expands
– Air cools to temp below dew pt, net condensation
causes clouds to form
– Condensation level-base of clouds
• Mixing-body of moist air mixes w/ another body
of moist air that has different temp
– Combination of air causes temp to change
• Lifting-air is forced upward when moving mass
of air meets sloping terrain, mt range, rising air
expands and cools, clouds form
• Advective cooling-temp of air mass decreases
as air mass moves over a cold surface
– Cold ocean or land surface
– Cold surface absorbs heat from air and cools it, air
cools to below dew pt, clouds form
Types of Clouds
• Classified by shape and altitude
• Stratus-flat, uniform base, low altitudes
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Base is low, close to Earth’s surface
Cover large area, block out sun
Little precipitation
Nimbostratus and altostratus
• Cumulus-low altitude, billowy, top that resembles cotton balls and
dark bottom
– Look fluffy
– Warm, moist air rises and cools, cooling air reaches dew pt, clouds form
• Cumulonimbus-high dark storm clouds
– Thunderheads
– Altocumulus and stratocumulus
• Cirrus-feathery clouds composed of ice crystals w/ highest altitude
– Altitudes of 6000 m
– Cirrocumulus and cirrostratus
Altocumulus-4000 m
Cumulonimbus-2000 to
6000 m
Cirrus-8000 m
Nimbostratus-1000 m
Fog
• What causes fog?
– Condensation of water vapor in air
• Forms from nightly cooling of Earth, air
comes in contact w/ chilled ground to
below dew pt, water vapor in air
condenses into droplets
• Thickest in valleys and low places. Why?
• Also thick around cities. Why?
Precipitation
• Define precipitation
– Any form of water that falls to Earth’s surface from the
clouds
• Rain, snow, sleet, hail
• Causes of precipitation
– Coalescence-formation of large droplet by
combination of smaller droplets
– Supercooling-condition in which substance is cooled
below its freezing pt, condensation pt, or sublimation
pt w/out going through a change of state
Measuring Precipitation
• Doppler Radar-can measure intensity of
precipitation
– Used by meteorologists for communicating
weather
– Bounces radio waves off rain or snow
– Determine the location, direction of
movement, intensity of precipitation
Weather Modifications
• Cloud seeding-introducing freezing nuclei
or condensation nuclei into a cloud to
cause rain to fall
• Uses silver iodide as freezing nuclei
• Use powdered dry ice, dropped from
aircraft to cool cloud droplets, cause ice
crystals to form