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ENVS 110

ENVS 110. 09-12-2008. atmospheric temperatures. seasonal changes daily changes temperature profile of the atmosphere horizontal temperature distributions global temperature distributions. earth’s orbit around the sun…. tilt of earth’s rotational axis.

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ENVS 110

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  1. ENVS 110 09-12-2008

  2. atmospheric temperatures • seasonal changes • daily changes • temperature profile of the atmosphere • horizontal temperature distributions • global temperature distributions

  3. earth’s orbit around the sun…

  4. tilt of earth’s rotational axis • during northern summer, northern hemisphere is tilted towards the sun • days are longer • sun is higher in the sky • how will this affect the temperatures ?

  5. flux again …

  6. spring and fall equinox

  7. (northern) summer solstice

  8. (northern) winter solstice

  9. due to the tilt of the earth’s axis • northern hemisphere experiences higher solar flux during summer months and • exposed to sunlight for longer period of time • receives more solar energy → warmer temperatures

  10. if earth’s orbit were circular… • both hemispheres would receive same amount of sunlight per year • but earth’s orbit is elliptical http://www.walter-fendt.de/ph11e/keplerlaw2.htm

  11. elliptical orbits • in circular orbits – orbiting velocity of planet does not change • in elliptical orbits it does • how does this influence the amount of sunlight received on the northern and southern hemisphere ? • homework assignment on web site (due on Wednesday)

  12. daily temperature changes • Remember – atmosphere is heated by conduction from the ground • Very thin boundary layer heats up first • Warm air expands and slowly rises • Optical properties of air depend on its density → objects close to ground are distorted

  13. daily temperature variations • Sun warms ground • Ground warms atmosphere • Highest air temperatures occur after noon because it takes some time to transfer heat from the ground into overlying air layers

  14. air temperature – Trinity College

  15. similar effect for seasonal temperatures

  16. role of moisture – latent heat • Boiling water stays at 100°C even though burner is left on • Where does all the extra energy go? • Evaporating water – water molecules are ripped apart → “hard work” = latent heat • Water vapor contains large amount of heat because water molecules are separated from each other

  17. ENVS 110 09-15-2008

  18. latent heat and air temperatures • Humid days: large amounts of solar energy are used to evaporate water • Air warms up slowly but contains lots of water vapor (which contains large amounts of latent heat) • Cooler but sticky !

  19. moisture and nighttime cooling • Air cools by giving off infrared radiation • Water vapor is a greenhouse gas • Water vapor contains large amounts of latent heat • When air cools water vapor condenses and turns back into droplets of water • Latent heat is released and heats surrounding air

  20. vertical temperature distributions • Troposphere is heated from below and cooled from the top • Atmospheric temperature decreases as you go up in elevation • Average temperature gradient: 6.5°C/km (3.5°F/1000 ft)

  21. http://www.fas.org/irp/imint/docs/rst/Sect14/Sect14_1a.html

  22. causes of variability in vertical temperature distributions • Underlying surface: • steeper gradient over continents • Shallower gradient over oceans • Oceans – cooler, moister air • Continents heat up faster, air often drier • Surface elevation • Higher elevation – thinner atmosphere = more rapid heat loss • High temperatures similar , nights much cooler

  23. horizontal temperature variations http://www.globalwarmingart.com/images/a/aa/Annual_Average_Temperature_Map.jpg

  24. Questions: • Where is the earth the warmest ? • Where does earth receive most of its solar energy ? • Why ? • Does this explain previous map?

  25. Solar flux at low latitudes • Solar flux highest if sun is (almost) directly overhead • Solar flux is highest on a clear day • How long is sun (almost) directly overhead at the equator ? • How long is sun (almost) disectly overhead in the tropics ?

  26. extent of the tropics

  27. the effects of the earth’s surface • Albedo • Heat capacity (specific heat) • Subsurface mixing

  28. Oceans / Continents Oceans • Water – high heat capacity • Variable albedo • Mix easily through waves etc. • Large evaporative losses Continents • Earth / rocks - low heat capacity • Immobile – no mixing, only thin surface layer warms rapidly • Little loss of latent heat (evaporation)

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