Unit 4.2: Atmospheric Composition and Weather Unit 4.2: Keep until June 2012! Unit 4.2: Atmospheric Composition and Weather

4 Atmospheric Layers: Troposphere: “tropos-” = change, turning Where air “turns over”, is mixed; most weather occurs here Temperatures ↓ as altitude ↑ b/c air molecules are farther apart, less able to conduct heat Contains 80% of atmosphere’s mass Tropopause: boundary between troposphere and stratrosphere; varies with location and season: Thicker in the tropics, thinner at the poles b/c of air temperature Thicker in summer, thinner in winter b/c of air temperature

Stratosphere: “strato-” = layered Temps ↑ as altitude ↑, why? Ozone layer (O3) in stratosphere absorbs UV radiation from the Sun – causes ↑ in temperature in this layer. Ozone layer protects living organisms from UV damage But chlorofluorocarbons (CFC’s) react with ozone, create “hole” in ozone layer

Mesosphere: “meso-” = middle Temps ↓ as altitude ↑ Meteors burn up in this layer Thermosphere: “thermo-” = heat Temps ↑ b/c atoms absorb high energy radiation, but b/c atoms are so far apart, does not feel hot! Also in this layer: Auroras, space station (ISS)

Composition of the Atmosphere: Major components: Nitrogen gas (N2): ~78% Oxygen gas (O2): ~21% Argon gas (Ar): >1% **Carbon dioxide (CO2): 0.036% Absorbs heat radiated from Earth to heat atmosphere

Variable components: Water vapor (H2O) Aerosols Absorbs Earth’s heat and solar energy When water changes state, it absorbs or releases heat “latent heat” Aerosols Microscopic particles: sea salts, fine soil, smoke/soot, pollen Provide “seed” to form clouds Can reflect/absorb solar radiation Partly responsible for red-orange sunset

Ozone: O3 O2 split by UV, single O combines with O2 to form O3 (O2 + O ↔ O3) Absorbs harmful UV, protects Earth’s surface Concentrated in stratosphere, not evenly Ozone fluctuates based on seasons: summer = more radiation, so more ozone, but air currents move it to poles Ozone hole - loss of ozone due to chlorofluorocarbon (CFC) pollution CFC’s break down O3, lose protective layer CFC’s from Styrofoam, hairspray propellants, refrigerant for air conditioners

CO2 and the Greenhouse effect: Solar radiation is high energy (UV, visible), passes through atmosphere easily, including greenhouse gases in atmosphere. Greenhouse gases: H2O, CO2, methane Earth absorbs, re-radiates infrared (IR) into atmosphere, but IR has less energy than incoming solar radiation. Greenhouse gases absorb IR, reflect it back to Earth’s surface instead of allowing it to escape into space. More gases = more IR absorption = higher temps. overall

Human activities that increase levels of GG: Burning coal/oil releases CO2 Deforestation – why? Trees capture CO2 in photosynthesis If fewer trees, then more CO2 into atmosphere Livestock management more methane

Composition of Venus’ atmosphere Atmospheres of Nearby Planets: Venus: density of atmosphere is 93 times that of Earth CO2 = ~95%, N2 =~4% Density and amount of CO2 = high temps on surface: ~467°C Venus has a “runaway greenhouse effect” b/c of dense CO2 Mars: density of atmosphere is <1% of Earth’s atmosphere CO2 = ~95%, N2 = ~2.7%; Ar = ~1.6% Mostly CO2, but so “rarefied”, no greenhouse effect Rarefied: less dense, spread out Composition of Venus’ atmosphere

III. Weather vs. Climate Weather: Climate: State of the atmosphere at a given place and time Constantly changing Climate: All weather that describes a particular place, region Both depend on 6 basic elements: Air temperature Humidity Cloudiness – type and amount Precipitation – type and amount Air pressure Speed and direction of wind

D. 6 Factors that Affect Temperature Latitude: closer to equator = higher temps More direct rays, less atmospheric interference Elevation/Altitude: Higher elevations are cooler b/c further away from heat generated at Earth’s surface Atmosphere is less dense (air is farther apart) as you rise in altitude so less heat is transferred

Differential heating of land/ water: Land surfaces are solid, absorb radiation at surface Water is transparent, can absorb more radiation below surface Heated water mixes, redistributes heat, so more stable Specific Heat: capacity to store thermal energy Water has high specific heat; Land has lower specific heat ... Land near water has more stable temps b/c water acts as a heat sink

Geographic Position: “Windward” coast has more moderate temps. Winds from ocean create more stable temps. “Leeward” coast temps are more like inland temps. Winds come from inland, subject to greater changes in temp. Mountains can create barrier, reduce oceanic effects of temperature stability Western side of Sierra-Nevada mtns. receives more rainfall than Eastern side of Sierra-Nevada. Nevada is a “rain-shadow desert”.

Cloud cover and albedo: Albedo: % of light reflected by an object Clouds reflect incoming solar radiation, keeps Earth’s surface cooler during daytime Clouds also reflect back infrared heat from Earth’s surface, keeps Earth’s surface warmer @ night

Ocean currents redistribute heat around Earth: Carries warmer water from equator  poles England warmer than should be b/c of this warmer water Currents from poles bring cooler water toward tropics Unit 4.2: Keep until June 2012! `