chapter 10

chapter 10 - Chapter 10 Planetary Atmospheres: Earth and...

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Chapter 10 Planetary Atmospheres: Earth and the Other Terrestrial Worlds
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10.1 Atmospheric Basics Our goals for learning What is an atmosphere? How does the greenhouse effect warm a planet? Why do atmospheric properties vary with altitude?
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What is an atmosphere? An atmosphere is a layer of gas that surrounds a world An atmosphere is a layer of gas that surrounds a world
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Earth’s Atmosphere About 10 km thick Consists mostly of molecular nitrogen (N 2 ) and oxygen (O 2 )
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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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Atmospheric Pressure Pressure and density decrease with altitude because the weight of overlying layers is less Earth’s pressure at sea level is 1.03 kg per sq. meter 14.7 lbs per sq. inch 1 bar
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Where does an atmosphere end? There is no clear upper boundary Most of Earth’s gas is < 10 km from surface, but a small fraction extends to >100 km Altitudes >60 km are considered “space”
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Where does an atmosphere end? Small amounts of gas are present even at > 300 km
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Effects of Atmospheres Create pressure that determines whether liquid water can exist on surface Absorb and scatter light Create wind, weather, and climate Interact with solar wind to create a magnetosphere Can make planetary surfaces warmer through greenhouse effect
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How does the greenhouse effect warm a planet?
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Greenhouse Effect Visible light passes through atmosphere and warms planet’s surface Atmosphere absorbs infrared light from surface, trapping heat
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Planetary Temperature A planet’s surface temperature is determined by balance between the energy of sunlight it absorbs and the energy of outgoing thermal radiation
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Temperature and Distance A planet’s distance from the Sun determines the total amount of incoming sunlight
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Temperature and Rotation A planet’s rotation rate affects the temperature differences between day and night
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Temperature and Reflectivity A planet’s reflectivity (or albedo ) is the fraction of incoming sunlight it reflects Planets with low albedo absorb more sunlight, leading to hotter temperatures
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“No Greenhouse” Temperatures Venus would be 510°C colder without greenhouse effect Earth would be 31°C colder (below freezing on average)
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What would happen to Earth’s temperature if Earth were more reflective? a) It would go up. b) It would go down. c) It wouldn’t change
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chapter 10 - Chapter 10 Planetary Atmospheres: Earth and...

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