10.1 Atmospheric Basics • Our goals for learning • What is an atmosphere? • How do you obtain an atmosphere?
What is an atmosphere? An atmosphere is a layer of gas that surrounds a world
How do you obtain an atmosphere? • Gain volatiles by comet impacts • outgassing during differentiation • Ongoing outgassing by volcanoes
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.
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
Earth’s Atmosphere • About 10 km thick • Consists mostly of molecular nitrogen (N2) and oxygen (O2)
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.
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
Temperatures and composition change with Height giving structure to an atmosphere
Earth’s Atmospheric Structure • Troposphere: lowest layer of Earth’s atmosphere • Temperature drops with altitude • Warmed by infrared light from surface and convection
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
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
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
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.
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?
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.
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.
Atmospheric Processes 2 Weather and Climate • Our goals for learning • What creates wind and weather?
Air Movement Gas molecules move from high density to lower density
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)
Atmospheric Circulation (convection) • Heated air rises at equator • Cooler air descends at poles Maximum Sun warming
Coriolis Effect Coriolis effect deflects north-south winds into east-west winds
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
Coriolis Effect Winds blow N or S Winds are diagonal Winds blow W or E Venus Earth Mars Jupiter, Saturn Neptune, Uranus(?)
Total Atmosphere Circulation
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
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
Factors that can Cause Long-Term Climate Change • Brightening of Sun • Changes in axis tilt • Changes in reflectivity • Changes in greenhouse gases
Changes in Greenhouse Gases • Increase in greenhouse gases leads to warming, while a decrease leads to cooling