Global-mean energy balance
Distribution of solar forcing as function of latitude
Spatial Radiation Imbalance
Top-of-atmosphere radiation imbalance
300
W/m2
EOUT (LW)
EIN (SW)
100
W/m2
Cause of the seasons
Cause of the seasons (better)
Seasonal cycle in net solar radiation
Seasonal cycle in terrestrial radiation (outgoing infrared)
Seasonal cycle in net radiation (solar minus terrestrial)
Seasonal cycle in temperature
Seasonal cycle in temperature – land responds quickly
Seasonal cycle in temperature – ocean responds slowly
Amplitude in seasonal cycle.
(at least) three things going on here…
In detail: insolation as a function of latitude
• Why are December and June not symmetric?
Hartmann, 1994
In detail: what does Earth do with this insolation?
• albedo as a function of latitude
• what causes this pattern?
Wells, 1997
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
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
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)
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
Aside: longwave (infrared) emissions to space as a function
of surface temperature
We’ve used Stefan Boltman law: longwave radiation = sT4
Make our lives easier:
From data:
n.b. why not use sT4?
longwave radiation = A + BT