19. atmospheric processes 2
TRANSCRIPT
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Chapter 10.1Planetary Atmospheres
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10.1 Atmospheric Basics
• Our goals for learning• What is an atmosphere?
• How do you obtain an atmosphere?
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What is an atmosphere?
An atmosphere is a layer of gas that surrounds a world
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How do you obtain an atmosphere?
– Gain volatiles by comet impacts
– outgassing during differentiation
– Ongoing outgassing by volcanoes
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Keeping an Atmosphere
• Atmosphere is kept by the world’s gravity– Low mass (small) worlds= low gravity =almost no atm.– High mass(large) worlds = high gravity = thick atm.
• Gravity and pressure– Air pressure depends on how much gas is
there ie. The atmospheric thickness.
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Gravity and Atmospheric Pressure• The stronger the gravity, the more gas is held by the world and the
greater the weight of atm. on a point
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Earth’s Atmosphere• About 10 km
thick
• Consists mostly of molecular nitrogen (N2) and oxygen (O2)
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Atmospheric Pressure
Gas pressure Gas pressure depends on both depends on both density and density and temperature.temperature.
Adding air Adding air molecules molecules increases the increases the pressure in a pressure in a balloon.balloon.
Heating the air Heating the air also increases also increases the pressure.the pressure.
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What do atmospheric properties vary with altitude?
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Light’s Effects on Atmosphere• Ionization: Removal
of an electron• Dissociation:
Destruction of a molecule
• Scattering: Change in photon’s direction
• Absorption: Photon’s energy is absorbed
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Temperatures and composition changewith Height giving structure to an atmosphere
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Earth’s Atmospheric Structure• Troposphere: lowest
layer of Earth’s atmosphere
• Temperature drops with altitude
• Warmed by infrared light from surface and convection
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Earth’s Atmospheric Structure• Stratosphere: Layer
above the troposphere
• Temperature rises with altitude in lower part, drops with altitude in upper part
• Warmed by absorption of ultraviolet sunlight
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Earth’s Atmospheric Structure• Thermosphere:
Layer at about 100 km altitude
• Temperature rises with altitude
• X rays and ultraviolet light from the Sun heat and ionize gases
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Earth’s Atmospheric Structure• Exosphere: Highest
layer in which atmosphere gradually fades into space
• Temperature rises with altitude; atoms can escape into space
• Warmed by X rays and UV light
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What have we learned?• What is an atmosphere?
– A layer of gas that surrounds a world
• How do you obtain an atmosphere?– comet impacts.– outgassing by differentiation, volcanoes,
• Why do atmospheric properties vary with altitude?– They depend on how atmospheric gases interact
with sunlight at different altitudes.
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Atmospheric Processes 1
• Our goals for learning
• What are the key processes?
• How does a planet gain or lose atmospheric gases?
• How does the greenhouse effect warm a planet?
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Atmospheric Processes
• Gaining and losing atmosphere– Gains: volcanic outgassing, impacts, evaporation.– Losses: gas escape,impacts,condensation,surface reactions
• Greenhouse Effect– Infrared energy is re-reflected back to the ground by CO2
• Atmospheric circulation (convection)– Convection cells move gas from equator to pole and back.
• Coriolis Effect– Gas dragged sideways by the rotation rate of the world.
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Atmospheric Gains
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Atmospheric Losses
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Greenhouse Effect
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Air Movement and Flow
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What have we learned?• There are 3 ways of adding to atmosphere
and 4 ways of depleting it.– Gas molecules can transfer out to space or
down to the ground.
• How does the greenhouse effect warm a planet?– Atmospheric molecules allow visible sunlight to
warm a planet’s surface but absorb infrared photons, trapping the heat.
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Atmospheric Processes 2 Weather and Climate
• Our goals for learning• What creates wind and weather?
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Air MovementGas molecules move from high density to lower density
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Atmospheric Pressure
Gas pressure depends on both density and temperature.
Adding air molecules increases the pressure in a balloon.
Heating the air also increases the pressure.(molecules more energetic)
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Atmospheric Circulation (convection)
• Heated air rises at equator
• Cooler air descends at poles
Maximum Sun warming
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Coriolis Effect
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Coriolis EffectCoriolis effect deflects north-south
winds into east-west winds
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Coriolis Effect breaks upGlobal Circulation
• On Earth the large circulation cell breaks up into 3 smaller ones, moving diagonally
• Other worlds have more or fewer circulation cells depending on their rotation rate
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Coriolis Effect
Winds blow N or S Winds blow W or EWinds are diagonal
Venus EarthMars
Jupiter, Saturn Neptune, Uranus(?)
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TotalAtmosphere Circulation
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What have we learned?• What creates wind and weather?
– Atmospheric heating and Coriolis effect.
– Solar warming creates convection cells.– The coriolis effect drags winds sideways
and breaks up the cells– The faster a planet spins, the more E-W
gas movement there is
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Weather and Climate• Weather is the ever-varying combination
of wind, clouds, temperature, and pressure– Local complexity of weather makes it difficult
to predict
• Climate is the long-term average of weather– Long-term stability of climate depends on
global conditions and is more predictable
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Factors that can Cause Long-Term Climate Change
• Brightening of Sun
• Changes in axis tilt
• Changes in reflectivity
• Changes in greenhouse gases
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Changes in Greenhouse Gases
• Increase in greenhouse gases leads to warming, while a decrease leads to cooling
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Global Warming
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Global Warming