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Mechanisms of ocean-atmosphere interactions

Mechanisms of ocean-atmosphere interactions. Arnaud Czaja SPAT PG lecture Oct. 2012. Atmosphere “feels” the ocean through:. Sea surface friction Sea surface heating/cooling:. Q. atmosphere. T o. ocean. Atmosphere “feels” the ocean through:. (Sea surface friction)

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Mechanisms of ocean-atmosphere interactions

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  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 To ocean

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

  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 Buoyancy of free atm (bf) advection Buoyancy of atm affected by Q(bs) Ta, qa Q To

  11. Over which atmospheric layer is Qlat+Qsen felt? • At same To, could observe very different atmospheric responses Situation when bs ≈bo << bf advection Ta, qa Shallow perturbation To

  12. Over which atmospheric layer is Qlat+Qsen felt? • At same To, could observe very different atmospheric responses Situation when bs ≈ bo ≈ bf Deep perturbation advection Ta, qa To

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

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

  15. Fraction of days with (Stp-Ssb < 0) in color & time mean SST (CI = 2⁰C) Frac DJF2004 DJF 2003-04 JJA2004 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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