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

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Presentation on theme: "Mechanisms of ocean- atmosphere interactions Arnaud Czaja SPAT PG lecture Oct. 2012."— Presentation transcript:

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 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...


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