Transcript PowerPoint Presentation - Precipitation Changes in Future

Global Change: Class Exercise
Global Energy Balance
&
Planetary Temperature
Mteor/Agron/Envsci/Envst 404/504
Zero-Dimensional, Global
Energy Balance Model
Zero-dimensional:
steady, time-average
averaged over all spatial directions
Global:
average is over the entire planet
Energy balance:
balance of incoming and outgoing energy flux
Global energy balance: Radiative equilibrium (in = out)
Zero-Dimensional GEBM
Incoming (absorbed) radiation:
At photosphere surface,
solar flux ~ 6.2.107 W-m-2
At Earth’s orbit, solar flux ~ 1360 W-m-2
Zero-Dimensional GEBM
Scattering:
air molecules, aerosols
Reflection: clouds
Planetary
Albedo
Surface albedo
Zero-Dimensional GEBM
Incoming (absorbed) radiation:
R
Incoming = (1-albedo) x (area facing sun) x S
= (1-)pR2S
Emitted radiation:
Outgoing = I x (4pR2)
R
Zero-Dimensional GEBM
Global energy balance: Radiative equilibrium (in = out)
Zero-Dimensional GEBM
Global energy balance: Radiative equilibrium (in = out)
Temperature ??
Zero-Dimensional GEBM
Suppose black-body emission:
What then is TRAD?
Zero-Dimensional GEBM
Observed, average surface temperature = Ts = 288 K
Why is Ts ≠ TRAD?
What about other planets?
How does Trad change with orbit?
Two Spheres Surrounding Sun
Total energy flux the same through each sphere
R2 = 2 x R 1
R2
R1
The same area at R2
intercepts only 1/4 of
energy it intercepts at R1
 Flux decreases as R-2
What about other planets?
How does Trad change with orbit?
Planet
Distance
from sun
Albedo
[A.U.]
Venus
0.72
0.76
Earth
1.00
0.30
Mars
1.52
0.16
Venus: Ts = 755 K
Outgoing IR
Trad
[W-m2]
[K]
238
255
Mars: Ts = 216 K
End - Class Exercise:
Global Energy Balance
&
Planetary Temperature