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Global-mean energy balance

Global-mean energy balance. Distribution of solar forcing as function of latitude. Spatial Radiation Imbalance. Top-of-atmosphere radiation imbalance. 300 W/m 2. E OUT (LW). E IN (SW). 100 W/m 2. Cause of the seasons. Cause of the seasons (better). Seasonal cycle in net solar radiation.

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Global-mean energy balance

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  1. Global-mean energy balance

  2. Distribution of solar forcing as function of latitude Spatial Radiation Imbalance

  3. Top-of-atmosphere radiation imbalance 300 W/m2 EOUT (LW) EIN (SW) 100 W/m2

  4. Cause of the seasons

  5. Cause of the seasons (better)

  6. Seasonal cycle in net solar radiation

  7. Seasonal cycle in terrestrial radiation (outgoing infrared)

  8. Seasonal cycle in net radiation (solar minus terrestrial)

  9. Seasonal cycle in temperature

  10. Seasonal cycle in temperature – land responds quickly

  11. Seasonal cycle in temperature – ocean responds slowly

  12. Amplitude in seasonal cycle. (at least) three things going on here…

  13. In detail: insolation as a function of latitude • Why are December and June not symmetric? Hartmann, 1994

  14. In detail: what does Earth do with this insolation? • albedo as a function of latitude • what causes this pattern? Wells, 1997

  15. In detail: energy balance as a function of latitude • Albedo • Absorbed insolation • (1-a) x incident insolation • Emitted terrestrial • radiation • Net radiation balance • (= absorbed radn • - emitted radn) Peixoto and Oort, 1992

  16. In detail: net radiation balance at top of atmosphere Poleward Heat flux More radiation is absorbed than emitted in the tropics more radiation is emitted than absorbed at high latitudes Implies an energy flux from the equator to the high latitudes

  17. In detail: net heat flux from tropics: Average radiation imbalance ~ 50 Wm-2 Surface Area of tropics = 2p Re2 sin (30o ) Total heat flux from tropics = surface area x imbalance = 6.4 x 1015 W = 10,000 times global energy production. = 1 Baringer size impact craters every 11 mins!! 1 Baringer = 109 tonnes of TNT (1 tonne TNT = 4.2 x 109 J)

  18. In detail: poleward heat transport Total 1 Petawatt = 1015W Ocean Atmosphere • Ocean transports more heat in low latitudes • (& net transport of heat across the equator) • Atmosphere transports more in middle and high latitudes Trenberth and Caron, 2001

  19. Aside: longwave (infrared) emissions to space as a function of surface temperature We’ve used Stefan Boltman law: longwave radiation = T4 Make our lives easier: longwave radiation = A + BT From data: n.b. why not use sT4?

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