global-mean energy balance
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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Global-mean energy balance
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Spatial Radiation Imbalance
Distribution of solar forcing as function of latitude
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100 W/m2
300 W/m2
EIN (SW)
EOUT (LW)
Top-of-atmosphere radiation imbalance
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Cause of the seasons
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Cause of the seasons (better)
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Seasonal cycle in net solar radiation
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Seasonal cycle in terrestrial radiation (outgoing infrared)
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Seasonal cycle in net radiation (solar minus terrestrial)
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Seasonal cycle in temperature
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Seasonal cycle in temperature – land responds quickly
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Seasonal cycle in temperature – ocean responds slowly
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Amplitude in seasonal cycle.
(at least) three things going on here…
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In detail: insolation as a function of latitude
Hartmann, 1994
• Why are December and June not symmetric?
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In detail: what does Earth do with this insolation?
• albedo as a function of latitude
Wells, 1997• what causes this pattern?
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• Albedo
• Absorbed insolation(1-) x incident insolation
• Emitted terrestrialradiation
• Net radiation balance (= absorbed radn - emitted radn)
In detail: energy balance as a function of latitude
Peixoto and Oort, 1992
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In detail: net radiation balance at top of atmosphere
PolewardHeat flux
More radiation is absorbed than emitted in the tropicsmore radiation is emitted than absorbed at high latitudes
Implies an energy flux from the equator to the high latitudes
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In detail: net heat flux from tropics:
Average radiation imbalance ~ 50 Wm-2
Surface Area of tropics = 2 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)
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In detail: poleward heat transport Total
Ocean Atmosphere
Trenberth and Caron, 2001
1 Petawatt = 1015W
• Ocean transports more heat in low latitudes (& net transport of heat across the equator)
• Atmosphere transports more in middle and high latitudes
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Aside: longwave (infrared) emissions to space as a function of surface temperature
n.b. why not use T4?
We’ve used Stefan Boltman law: longwave radiation = T4
Make our lives easier: longwave radiation = A + BT
From data: