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

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

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

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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)

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

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

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

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

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

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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

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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

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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

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

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

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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

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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

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Response of the atmosphere to a prescribed heating / cooling

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

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Friday session...

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Flux of mass in (kg/s) = Flux of mass out (kg/s) = Net Flux of mass in ‘x’ = Net Flux of mass in ‘y’ = Net Flux of mass in ‘z’ =, u, w, v Mass per volume.

Flux of mass in (kg/s) = Flux of mass out (kg/s) = Net Flux of mass in ‘x’ = Net Flux of mass in ‘y’ = Net Flux of mass in ‘z’ =, u, w, v Mass per volume.

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