1. Mechanisms of ocean- atmosphere interactions Arnaud Czaja SPAT PG lecture Oct. 2012

2. Atmosphere “feels” the ocean through: Sea surface friction Sea surface heating/cooling: Q atmosphere ocean ToTo

3. Atmosphere “feels” the ocean through: (Sea surface friction) Sea surface heating/cooling: Q atmosphere ocean ToTo Radiative + “sensible” + “latent”

4. Ocean – atmosphere heat exchange Radiative = solar (up and down) and longwave (up and down). Net heating of the ocean. Sensible & latent: bring the surface atmosphere into thermodynamic equilibrium with the ocean (Ta=To and RH = 100%). Net cooling of the ocean. NB: following slides show these fluxes from the ERA40 atlas website (very useful web resource)

5. Net longwave ↓+↑ flux climatology (Wm-2, positive downwards) Annual mean DJF JJA

6. Net shortwave ↓+↑ flux climatology (Wm-2, positive downwards) Annual mean DJF JJA

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

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

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

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

11. 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

12. 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

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

14. Global Infrared image Tropics: “spotty” (convection organized in random clusters) Extra-Tropics: “wavy” (convection organized by Jet Stream meanders)

15. DJF2004 JJA2004 Frac Fraction of days with (S tp -S sb < 0) in color & time mean SST (CI = 2⁰C) DJF 2003-04 JJA 2004 ERAint data

16. 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) Q6

17. Response of the atmosphere to a prescribed heating / cooling

18. “Gill’s response” to heating (1980) Q7

19. Friday session...