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Mechanisms of ocean-atmosphere interactions
Arnaud CzajaSPAT PG lecture Nov. 2011
Atmosphere “feels” the ocean through:
• Momentum exchanges (friction)
• Surface heat exchanges
Q atmosphere
ocean
To
Atmosphere “feels” the ocean through:
• Momentum exchanges
• Surface heat exchange
Q atmosphere
ocean
To
Radiative+
“sensible”+
“latent”
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.
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 an 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
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)
“Gill’s response” to heating (1980)
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!
Relevance of Hoskins/Karoly?
• Midlatitudes: does not take into account the weather (travelling baroclinic waves)...
Friday session...
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