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Temperature Structure of the Atmosphere Chapter 5

Temperature Structure of the Atmosphere Chapter 5. Greenhouse effect is powered by lapse rate. Has to be cold higher in atm. Have to add in processes not found in layer model Need moist convection. T structure of atm is coupled to T of ground by convection. Warm air rises and carries heat

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Temperature Structure of the Atmosphere Chapter 5

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  1. Temperature Structure of the AtmosphereChapter 5

  2. Greenhouse effect is powered by lapse rate. • Has to be cold higher in atm. • Have to add in processes not found in layer model • Need moist convection

  3. T structure of atm is coupled to T of ground by convection. • Warm air rises and carries heat • As it expands, it cools. • Leads to dec. in T with inc. altitude. • If atm were incompressible, like water, there would be little change in T with altitude. • no gh effect because amount of outgoing IR would be the same whether it came from the ground or high in the atm.

  4. Typical T and P of atm as a function of altitude • Troposhpere - 90% of gas molecules, weather, climate models • Stratosphere • More layers above…. • P nonlinear with altitude (exponential)

  5. Fig. 5.2 - P and depth are linear • Water is not compressible • So it increases linearly with depth

  6. Adiabatic expansion • Lapse rate - T dec. w/altitude • Adiabatic - air heats/cools by expansion/compression, not due to T of air around it. • Dry vs. moist

  7. Sinking = compressing = heating

  8. Effect of water on the T profile of atm. • Air cools as it rises, water vapor condenses to droplets, releases LH. • So, moist adiabatis less than dry.

  9. Water vapor & latent heat • 3 phases of water • Vapor = liquid + heat • Latent heat = energy tied up in water vapor • Sensible heat – what we measure with a thermometer • Condensation - LH SH

  10. Convection • Carries heat (along with radiation and conduction) • Transfers heat from equator to poles • Occurs in fluids (liquid & gas) • Driven by heating from below • Molecules move energetically, fluid expands, density decreases. Heating from below Stable

  11. Convection in the layer model • Layer model from chapter 3 didn’t have convection. • T of atm. layer decreases with altitude • But, in earlier model, heat is only carried upward by radiation. • Need to add convection to the model.

  12. C 3000 m B 0 m A D 0 m DALR = 10 deg C/Km Point A: T = 30 deg C Point B: T = 20 deg C SALR = 6 deg C/Km Point C: T = 8 deg C Point D: T = 38 deg C 1000 m

  13. Convection in the layer model If we add convection to the layer model then we have to add another set of heat arrows.

  14. Lapse rate & gh effect • The steeper the lapse rate, the stronger the gh effect. • If the atm were incompressible , like water, and convection maintained a uniform T w/altitude then there would be no gh effect. • Raise CO2 in atm raises the altitude in the atm where IR escapes to space. A to B - Inc. amount of gh gas. IR to space at a higher altitude (new skin altitude). But, the skin T stays the Same (red line). Inc. in skin T altitude -- inc. ground T A B A

  15. Take Home Points • Air in the upper troposphere is colder due to moist convection. • Sunlight heats surface, air rises and cools • P decreases with altitude • T decreases as a gas expands • LH is released as SH as water vapor condenses. • Lapse rate is controlled by the moist adiabat. • Strength of gh effect depends on the lapse rate. • Need another set of arrows in our model!!

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