1. Observational Physical Oceanography 12.808
Introduction to
Observational Physical Oceanography
12.808
Class 8, 6 October 2009
1:05 to 2:25
these slides are available online at

2. Section 4: Air-Sea (and Space) Interaction
1) energy budget for the Earth in space
2) inference of meridional energy transport
by the atmosphere and ocean
3) mechanisms of energy transport by the
atmosphere and ocean
4) observing heat fluxes at the ocean surface
5) fresh water flux
6) heat storage on diurnal and seasonal time scales
today's
topics

3. Energy comes in from space as solar radiation. Energy is
transformed and transported over the Earth by the atmosphere
and ocean, and re-emitted back to space. Energy budgets can be
defined for a variety of space and time volumes to reveal one or
another aspect of this crucial process.

4. this emphasizes transformations in a column of the atmosphere
energy balance for the
global, annual mean.
this emphasizes transformations
in a column of the atmosphere E S Qs Qh Qe Qb
from Stewart 05

5. space
Earth Qs Qh Qe Qb
from Stewart 05

6. Energy flux in space is by radiative fluxes that
may be measured by satellites.
space
Earth Qs Qh Qe Qb
from Stewart 05

7. a one box model of Earth
floating in space
So = 1366 W/m^2
So varies with Earth-sun distance;
1321 in NH summer,
1412 in NH winter.
on global, annual avg,
S = So/4 =
342 W/m^2
So varies with the 11 year
sunspot cycle by 0.05%
Earth (atmosphere and ocean)
Minor variation of So would have (does have?)
a very significant impact on Earth’s climate.

8. a one box model of Earth
floating in space
some solar radiation is reflected and
never absorbed. this fraction is
the albdeo, a = 0.34; Earth is bright.
S = So/4 =
342 W/m^2
a S
Earth (atmosphere and ocean)
Albedo is due to clouds, aerosols and ice and can in principle be quite variable. Small changes in albedo can cause very large changes in climate.

9. the steady energy balance for Earth as a whole (integrated):
S0 = 1376 W m-2
a = albedo ~ 0.3 aS
the steady energy balance for Earth as a whole (integrated):
S0(1 - a) + E = 0 E
E = long wave out

10. Earth's energy balance is Approx. steady, so there must
be an energy flux of
radiation emitted to space,
E is long wave (infrared) radiation.
S = S0/4 =
342 W/m^2 E aS
Earth = atmosphere + ocean +
land
If steady, the net radiation, Q = S( 1 – a) + E = 0.
Deviations due to storage are the order of 0.3 W m-2.

11. An aside......
We (oceanographers) seem fixated on energy
and energy budgets.
The total amount of energy that Earth receives from
the sun and reradiates to space is very close to zero.
Makes you wonder ….. is the amount of this energy all
that matters?

12. Life is possible on Earth thanks to a steady stream of low
Exchange with space is in balance, so what keeps Earth/life running?
A steady flux of high quality energy. Earth receives high frequency,
low entropy photons from the sun, T = 5800 K, and sends
back a much larger number of mainly low frequency, infrared,
T = 255 K, photons that have higher entropy.
Infrared radiation;
high entropy,
low quality
Solar radiation;
low entropy,
high quality
atmosphere and ocean
Life is possible on Earth thanks to a steady stream of low
entropy (high quality) energy that comes from the Sun.

13. Entropy - that's about all we will say. If you want to know more,
take a look at:

14. Back to our budgets......averaging over the entire Earth seems
a little coarse; let’s divide the box it into two pieces by latitude: S1 E1 S2 E2 Q2 Q1
Q1 > 0
net radiation warms
Q2 < 0
net radiation cools
box 1,
low latitude
box 2,
high latitude
An overall balance still holds, Q1 + Q2 = 0.
And within each box we also expect a steady state.

15. the steady energy balance for Earth as a whole:
S0 = 1376 W m-2
a = albedo ~ 0.3
aS0
the steady energy balance for Earth as a whole:
S0(1 - a) + E = 0 E
E = long wave out

16. Earth’s radiation balance with space measured by satellites:
S varies strongly with latitude, while E varies less S E Q
Q =
S - E
from Bryden, 2001

17. low latitudes show
a gain of energy by net
radiation, up to about
100 W/m^2
high latitudes show
a loss of energy by
radiation, up to about
-100 W/m^2
Q1 > 0
Q2 < 0
box 2,
high latitude
box 1,
low latitude
If the climate is nearly in steady state, A1*Q1 + A2*Q2 = 0,
then how is an energy balance achieved within each box?

18. By an energy (heat) transport, F, carried by the atmosphere and
high latitudes show
a loss of energy by net
radiation, up to about
-100 W/m^2
low latitudes show
a gain of energy by net
radiation, up to about
100 W/m^2 Q1 Q2
Area = A1
F = A1*Q1 =
-A2*Q2
box 1,
low latitude
high latitude
By an energy (heat) transport, F, carried by the atmosphere and
ocean: a fundamental aspect of the atmosphere and ocean.

19. By an energy (heat) transport, F, carried by the atmosphere and
high latitudes show
a loss of energy by net
radiation, up to about
-100 W/m^2
low latitudes show
a gain of energy by net
radiation, up to about
100 W/m^2 Q1 Q2
Area = A1
F = 0
on the ends
F = A1*Q1 =
-A2*Q2
box 1,
low latitude
high latitude
By an energy (heat) transport, F, carried by the atmosphere and
ocean: a fundamental aspect of the atmosphere and ocean.

20. If we can assume steady state, then it follows that
the sum of all energy fluxes into a control volume must be zero.
net radiation
gain
net radiation
deficit
net radiation
deficit
Q2 = -2*Q3
Q area = A
Q1=Q3
F = 0
F2 = Q1*A
F3 -= Q3*A
(units are Watts)
F = 0
high latitude
low latitude
high latitude
We can estimate the internal, a-o energy transport, F, on the sides of boxes
over which we know the net radiative heat flux, Q.

21. Pop Quiz

22. Pop Quiz net radiation is a gain = Q net radiation net radiation
Is a deficit = -Q/2
net radiation
Is a deficit = -Q/2
area = A
for all boxes 1 2 3 4
what is the energy transport at 1, 2, 3, 4 ?

23. for any control volume in
Radiation balance method Q
Q= net radiation flux to space
F = energy transport in
atmos + ocean
for any control volume in
steady state:
Q*A + F = 0 F F
for a polar cap:
Q is a heat loss
F is a heat gain due to
atmosphere and ocean
heat transport

24. Earth’s radiation balance with space:
S is strongly dependent upon latitude; E is much less so S E
loses
heat
loses
heat Q
gains heat by radiation
Q =
S - E
from Bryden, 2001

25. positive means meridional energy transport F is going northward
max value is about 6 x1015 W
from Bryden, 2001
F = meridional energy transport
atmosphere + ocean
computed from Q(lat)
positive means meridional energy transport F is going northward
(note the units, energy/time…..)

26. The ocean carries a significant fraction of the net meridional
from Bryden, 2001
ocean energy transport
computed as
total - atmosphere
The ocean carries a significant fraction of the net meridional
energy transport; more than atmosphere at low lat., less at high lat.
To know the ocean contribution separately, we have to do more….

27. when we return, Breck Owens and Argo floats
take a short break
when we return, Breck Owens and Argo floats