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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) - PowerPoint PPT Presentation
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Mechanisms of ocean-atmosphere interactions
Arnaud CzajaSPAT PG lecture Oct. 2012
Atmosphere “feels” the ocean through:
• Sea surface friction
• Sea surface heating/cooling:
Q atmosphere
ocean
To
Atmosphere “feels” the ocean through:
• (Sea surface friction)
• Sea surface heating/cooling:
Q atmosphere
ocean
To
Radiative+
“sensible”+
“latent”
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)
Net longwave ↓+↑ flux climatology (Wm-2, positive downwards)
Annual mean
DJF JJA
Net shortwave ↓+↑ flux climatology (Wm-2, positive downwards)
Annual mean
DJF JJA
Sensible heat flux climatology (Wm-2)
Annual mean
DJF JJA
Latent heat flux climatology (Wm-2)
Annual mean
DJF JJA
Net heat flux climatology (Wm-2)
Annual mean
DJF JJA
Over which atmospheric layer is Q=Qlat+Qsen felt?
• For given To, destabilize atm by advecting a thermodynamically unbalanced air mass
To
advection
Buoyancy offree atm (bf)
Buoyancy ofatm affected
by Q(bs)QTa, qa
Over which atmospheric layer is Qlat+Qsen felt?
• At same To, could observe very different atmospheric responses
advection
Situation whenbs ≈bo << bf
Ta, qa
To
Shallow perturbation
Over which atmospheric layer is Qlat+Qsen felt?
• At same To, could observe very different atmospheric responses
advection
Situation when bs ≈ bo ≈ bf
Ta, qa
To
Deep perturbation
Atm. heating rate climatology (K/day)
Annual mean
DJF JJA
Global Infrared image
Tropics: “spotty” (convection organized in random clusters)Extra-Tropics: “wavy” (convection organized by Jet Stream meanders)
DJF2004
JJA2004
FracFraction of days with (Stp-Ssb < 0) in color & time mean SST (CI = 2⁰C)
DJF 2003-04
JJA 2004ERAint data
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
Response of the atmosphere to a prescribed heating / cooling
“Gill’s response” to heating (1980)
Q7
Friday session...
