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 http://www.whoi.edu/science/PO/people/jprice/class/miscart/Class8-06Oct09.ppt

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

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.

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

space Earth Qs Qh Qe Qb from Stewart 05

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

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.

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.

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 www.trueearth.com

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.

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?

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.

Entropy - that's about all we will say. If you want to know more, take a look at: www.whoi.edu/science/PO/people/jprice/class/miscart/entropy.zip

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.

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 www.trueearth.com

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

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?

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.

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.

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 Q3 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.

Pop Quiz

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 ?

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 www.trueearth.com

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

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…..)

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….

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