1. Mechanisms of ocean- atmosphere interactions Arnaud Czaja SPAT PG lecture Nov. 2011

2. Atmosphere “feels” the ocean through: Momentum exchanges (friction) Surface heat exchanges Q atmosphere ocean ToTo

3. Atmosphere “feels” the ocean through: Momentum exchanges Surface heat exchange Q atmosphere ocean ToTo Radiative + “sensible” + “latent”

4. Ocean – atmosphere heat exchange Radiative = solar (up and down) and longwave (up and down). Weakly dependent upon To and hence upon ocean currents, thermocline depth, etc. Sensible & latent: bring the surface atmosphere into thermodynamic equilibrium with the ocean (Ta=To and RH = 100%). Very strongly dependent upon To.

5. Sensible heat flux climatology (Wm-2) Annual mean DJF JJA

6. Latent heat flux climatology (Wm-2) Annual mean DJF JJA

7. Net heat flux climatology (Wm-2) Annual mean DJF JJA

8. Over which atmospheric layer is Q=Qlat+Qsen felt? For given To, destabilize atm by advecting an unbalanced air mass ToTo advection Buoyancy of free atm (bf) Buoyancy of atm affected by Q(bs) Q T a, q a

9. Over which atmospheric layer is Qlat+Qsen felt? At same To, could observe very different atmospheric responses advection Situation when bs ≈bo << bf T a, q a ToTo Shallow perturbation

10. Over which atmospheric layer is Qlat+Qsen felt? At same To, could observe very different atmospheric responses advection Situation when bs ≈ bo ≈ bf T a, q a ToTo Deep perturbation

11. Atm. heating rate climatology (K/day) Annual mean DJFJJA

12. Global Infrared image

13. Response of the atmosphere to a prescribed heating / cooling Linear calculations on the board Follows the classic paper by Hoskins and Karoly (J. Atm. Sci., 1981)

14. “Gill’s response” to heating (1980)

15. Relevance of Hoskins/Karoly? Tropics: condensational heating occurs in cloud clusters and is balanced partly by upward motion in clouds and radiative cooling in the subsiding air in between clouds  hard to know what to choose for Q!

16. Relevance of Hoskins/Karoly? Midlatitudes: does not take into account the weather (travelling baroclinic waves)...

17. Friday session...