global-mean energy balance

Global-mean energy balance

Spatial Radiation Imbalance

Distribution of solar forcing as function of latitude

100 W/m2

300 W/m2

EIN (SW)

EOUT (LW)

Top-of-atmosphere radiation imbalance

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

Hartmann, 1994

• Why are December and June not symmetric?

In detail: what does Earth do with this insolation?

• albedo as a function of latitude

Wells, 1997• what causes this pattern?

• 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

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

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)

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

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: