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Lecture 11 Atmosphere

Lecture 11 Atmosphere - Outline Introduc/ontotheatmosphere...

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3/1/09 1 Lecture 11: The Atmosphere Suggested Readings: KKC Chapter 3 (on Blackboard) Outline: Introduc/on to the atmosphere Electromagne/c radia/on and Earth’s heat budget The greenhouse effect Atmospheric composi/on and structure Earth’s atmosphere •Mixture of gas molecules that surrounds the planet •Held close to the planet by gravity •Some gases are chemically inert (inac1ve) •Others are chemically reacAve •Some contribute to the greenhouse effect (absorb infrared radiaAon) •Others absorb ultraviolet radiaAon Major gases in the atmosphere (concentra1on by % volume) 1. Nitrogen, N 2 78% 2. Oxygen, O 2 21% 3. Argon, Ar 0.9% 4. Water vapor, H 2 O range 0.00001% (polar) to 4% (tropics) 5. Carbon dioxide, CO 2 0.0385% (385 ppm) These five account for > 99.9% of all gases molecules in the atmosphere Increased from 280 ppm since the 19 th century
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3/1/09 2 Pressure decreases with increasing alAtude (exponenAally) Temperature profile is more complex due to changes in atmospheric composiAon Terms: Electromagne/c radia/on : Self propagaAng electric and magneAc wave, similar to waves on the surface of a pond 1. Wavelength 2. Frequency 3. ElectromagneAc spectrum Blackbody : Something that emits (or absorbs) electromagneAc radiaAon at 100% efficiency at all wavelengths The amount of energy emiZed by a blackbody is a funcAon of its temperature Hydrogen fusion in the sun creates energy (sun is a blackbody) When this energy reaches Earth: 70% is absorbed 30% is reflected away by oceans, ice, other ‘reflec/ve’ surfaces Earth’s reflec/vity is called it’s albedo (Earth’s albedo is 0.3)
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