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Mechanisms of ocean-atmosphere interactions

Mechanisms of ocean-atmosphere interactions. Arnaud Czaja SPAT PG lecture Nov. 2011. Atmosphere “feels” the ocean through:. Momentum exchanges (friction) Surface heat exchanges. Q. atmosphere. T o. ocean. Atmosphere “feels” the ocean through:. Momentum exchanges Surface heat exchange.

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Mechanisms of ocean-atmosphere interactions

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  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 To ocean

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

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

  9. 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

  10. 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

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

  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...

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