ANALYSIS OF THERMOHALINE FEEDBACKS
JOCHEM MAROTZKE
Massachusetts Institute of Technology
Cambridge, USA
Contents
1 Introduction
2 Model formulation
2.1
Basic equations
2.2 Surface heat fluxes . . . .
2.3 Surface freshwater fluxes.
2.4 Equilibrium solutions. . .
3 Stability of the high-latitude sinking equilibrium
3.1 Atmospheric transport anomalies
3.2 Modelling strategy . . .
3.3 Thermohaline feedbacks
4 Land effects
4.1 Basic equations . . . . . . . .
4.2 Spatially averaged quantities
4.3 Meridional gradients . . . . .
5 Flux adjustments and climate drifts
6 The 'neutrally buoyant mode'
7 Concluding remarks
Abstract
Feedbacks between atmospheric meridional transports and the thermohaline circulation (THO) are analysed, using a four-box ocean-atmosphere model in one hemisphere. The ocean model is Stommel's; the atmospheric model is similar to the one
developed earlier by Marotzke and Stone and gives the surface heat and freshwater fluxes as residuals of the atmospheric energy and moisture budgets, assumed in
balance. Radiation at the top of the atmosphere depends linearly on surface temperature; atmospheric meridional heat and moisture transports are proportional to an
arbitrary positive power of the meridional temperature gradient, which is taken to be
identical to the oceanic temperature gradient. The coefficients in the power laws for
atmospheric meridional transports are chosen such that all coupled models have one
steady state in common. Upon linearization, a Newtonian cooling law is derived for
anomalous differential surface heat flux. The timescale on which the ocean temperature gradient is restored decreases with increasing power, n, in the atmospheric heat
NATO AS! Series. Vol. ! 44
Decadal Climate Variability
Dynamics and Predictability
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Edited by David L. T. Anderson and Jlirgen Willebrand
© Springer-Verlag Berlin Heidelberg 1996
JOCHEM MAROTZKE
Massachusetts Institute of Technology
Cambridge, USA
Contents
1 Introduction
2 Model formulation
2.1
Basic equations
2.2 Surface heat fluxes . . . .
2.3 Surface freshwater fluxes.
2.4 Equilibrium solutions. . .
3 Stability of the high-latitude sinking equilibrium
3.1 Atmospheric transport anomalies
3.2 Modelling strategy . . .
3.3 Thermohaline feedbacks
4 Land effects
4.1 Basic equations . . . . . . . .
4.2 Spatially averaged quantities
4.3 Meridional gradients . . . . .
5 Flux adjustments and climate drifts
6 The 'neutrally buoyant mode'
7 Concluding remarks
Abstract
Feedbacks between atmospheric meridional transports and the thermohaline circulation (THO) are analysed, using a four-box ocean-atmosphere model in one hemisphere. The ocean model is Stommel's; the atmospheric model is similar to the one
developed earlier by Marotzke and Stone and gives the surface heat and freshwater fluxes as residuals of the atmospheric energy and moisture budgets, assumed in
balance. Radiation at the top of the atmosphere depends linearly on surface temperature; atmospheric meridional heat and moisture transports are proportional to an
arbitrary positive power of the meridional temperature gradient, which is taken to be
identical to the oceanic temperature gradient. The coefficients in the power laws for
atmospheric meridional transports are chosen such that all coupled models have one
steady state in common. Upon linearization, a Newtonian cooling law is derived for
anomalous differential surface heat flux. The timescale on which the ocean temperature gradient is restored decreases with increasing power, n, in the atmospheric heat
NATO AS! Series. Vol. ! 44
Decadal Climate Variability
Dynamics and Predictability
334
336
336
339
341
343
346
346
348
349
357
357
358
359
363
368
373
Edited by David L. T. Anderson and Jlirgen Willebrand
© Springer-Verlag Berlin Heidelberg 1996