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

2. 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

3. 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

4. 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)

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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”.

15. 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 night

16. 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! `