Unit 4.2: Atmospheric Compositionand Weather

I. 4 Atmospheric Layers:A. Troposphere: “tropos-” = change,

turning1. Where air “turns over”, is mixed;

most weather occurs here2. Temperatures ↓ as altitude ↑ b/c

air molecules are farther apart, less able to conduct heat

3. Contains 80% of atmosphere’s mass4. Tropopause: boundary between

troposphere and stratrosphere; varies with location and season:a. Thicker in the tropics, thinner at the

poles b/c of air temperatureb. Thicker in summer, thinner in winter

b/c of air temperature2

B. Stratosphere: “strato-” = layered1. Temps ↑ as altitude ↑,

why?2. Ozone layer (O3) in

stratosphere absorbs UV radiation from the Sun – causes ↑ in temperature in this layer.a. Ozone layer protects living

organisms from UV damageb. But chlorofluorocarbons

(CFC’s) react with ozone, create “hole” in ozone layer

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C. Mesosphere: “meso-” = middle1. Temps ↓ as altitude ↑2. Meteors burn up in this layer

D. Thermosphere: “thermo-” = heat1. Temps ↑ b/c atoms absorb

high energy radiation, but b/c atoms are so far apart, does not feel hot!

2. Also in this layer: Auroras, space station (ISS)

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II. Composition of the Atmosphere:A. Major components:

1. Nitrogen gas (N2): ~78%

2. Oxygen gas (O2): ~21%

3. Argon gas (Ar): >1%4. **Carbon dioxide (CO2): 0.036%

a. Absorbs heat radiated from Earth to heat atmosphere

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B. Variable components:1. Water vapor (H2O)

a. Absorbs Earth’s heat and solar energy

b. When water changes state, it absorbs or releases heat • “latent heat”

2. Aerosolsa. Microscopic particles: sea salts,

fine soil, smoke/soot, pollenb. Provide “seed” to form cloudsc. Can reflect/absorb solar

radiationd. Partly responsible for red-

orange sunset6

3. Ozone: O3a. O2 split by UV, single O combines with O2

to form O3 (O2 + O ↔ O3)

b. Absorbs harmful UV, protects Earth’s surface

c. Concentrated in stratosphere, not evenly1) Ozone fluctuates based on seasons: summer

= more radiation, so more ozone, but air currents move it to poles

d. Ozone hole - loss of ozone due to chlorofluorocarbon (CFC) pollution1) CFC’s break down O3, lose protective layer

2) CFC’s from Styrofoam, hairspray propellants, refrigerant for air conditioners

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C. CO2 and the Greenhouse effect:1. Solar radiation is high energy (UV,

visible), passes through atmosphere easily, including greenhouse gases in atmosphere.a. Greenhouse gases: H2O, CO2,

methane2. Earth absorbs, re-radiates infrared (IR)

into atmosphere, but IR has less energy than incoming solar radiation.

3. Greenhouse gases absorb IR, reflect it back to Earth’s surface instead of allowing it to escape into space.

4. More gases = more IR absorption = higher temps. overall

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D. Human activities that increase levels of GG:1. Burning coal/oil releases CO2

2. Deforestation – why?• Trees capture CO2 in photosynthesis

• If fewer trees, then more CO2 into atmosphere

3. Livestock management• more methane

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E. Atmospheres of Nearby Planets:1. Venus: density of atmosphere is 93 times that of Earth

a. CO2 = ~95%, N2 =~4%

b. Density and amount of CO2 = high temps on surface: ~467°C

c. Venus has a “runaway greenhouse effect” b/c of dense CO2

2. Mars: density of atmosphere is <1% of Earth’s atmospherea. CO2 = ~95%, N2 = ~2.7%; Ar = ~1.6%

b. Mostly CO2, but so “rarefied”, no greenhouse effect1) Rarefied: less dense, spread out

Composition of Venus’ atmosphere

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III. Weather vs. ClimateA. Weather:

1. State of the atmosphere at a given place and time

2. Constantly changing

B. Climate:1. All weather that describes a particular

place, region

C. Both depend on 6 basic elements:1. Air temperature2. Humidity3. Cloudiness – type and amount4. Precipitation – type and amount5. Air pressure6. Speed and direction of wind 11

D. 6 Factors that Affect Temperature1. Latitude: closer to equator =

higher tempsa. More direct rays, less

atmospheric interference

2. Elevation/Altitude: a. Higher elevations are cooler

b/c further away from heat generated at Earth’s surface

b. Atmosphere is less dense (air is farther apart) as you rise in altitude so less heat is transferred

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3. Differential heating of land/ water:a. Land surfaces are solid, absorb radiation at surfaceb. Water is transparent, can absorb more radiation below

surface1) Heated water mixes, redistributes heat, so more stable2) Specific Heat: capacity to store thermal energy

• Water has high specific heat; Land has lower specific heat

c. ... Land near water has more stable temps b/c water acts as a heat sink

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4. Geographic Position:a. “Windward” coast has more moderate temps.

1) Winds from ocean create more stable temps.

b. “Leeward” coast temps are more like inland temps.1) Winds come from inland, subject to greater changes in temp.

c. Mountains can create barrier, reduce oceanic effects of temperature stability1) Western side of Sierra-Nevada mtns. receives more rainfall than

Eastern side of Sierra-Nevada. Nevada is a “rain-shadow desert”.

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5. Cloud cover and albedo:• Albedo: % of light

reflected by an objecta. Clouds reflect incoming

solar radiation, keeps Earth’s surface cooler during daytime

b. Clouds also reflect back infrared heat from Earth’s surface, keeps Earth’s surface warmer @ night

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6. Ocean currents redistribute heat around Earth:a. Carries warmer water from equator poles

1) England warmer than should be b/c of this warmer water

b. Currents from poles bring cooler water toward tropics

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