Planetary Engineering 1Planetary Engineering 1

Climate ModelingClimate Modeling

Class ExerciseClass Exercise

Global energy balance: Radiative equilibrium (in = out)

Zero-Dimensional GEBMZero-Dimensional GEBM

Goal: PlanetsGoal: Planets’’ Temperatures Temperatures

Important Factor: How does S change with orbit? Important Factor: How does S change with orbit?

Important Fact: Sun heats less the farther it is. Important Fact: Sun heats less the farther it is.

At photosphere surface, At photosphere surface, solar flux ~ 6.2solar flux ~ 6.2..101077 W-m W-m-2-2

Change in solar flux: sun earth

At EarthAt Earth’’s orbit, solar flux ~ 1360 W-ms orbit, solar flux ~ 1360 W-m-2-2

Recall from Topic 1:Recall from Topic 1:

RR22 = 2 x R = 2 x R11

Total energy flux the same through each sphere

Two Spheres Surrounding SunTwo Spheres Surrounding Sun

RR22

RR11

The same area at RThe same area at R22

intercepts only 1/4 of intercepts only 1/4 of energy it intercepts at Renergy it intercepts at R11

Flux decreases as RFlux decreases as R-2-2

Global energy balance: Radiative equilibrium (in = out)

For EarthFor Earth

Thus, TRAD = 255 K

What about other planets?What about other planets?

How does THow does Tradrad change with orbit? change with orbit?

What about other planets?What about other planets?

How does THow does Tradrad change with orbit? change with orbit? Planet Distance Albedo Outgoing IR Trad

from sun[A.U.] [W-m2] [K]

Mercury 0.39 0.06

Venus 0.72 0.76

Earth 1.00 0.30 238 255

Mars 1.52 0.16

Jupiter 5.20 0.51

Saturn 9.54 0.50

Uranus 19.18 0.66

Neptune 30.06 0.62

Tsurface ≈ Trad. How warm can we make its surface?

For MarsFor Mars

Tsurface ≈ Trad. How cool can we make its surface?

For MercuryFor Mercury

Why can’t we adjust Venus the same way?

Venus?Venus?

End End Planetary Engineering 1 Planetary Engineering 1