On the contribution of the subtropical gyre to
the meridional heat transport in an idealized OGCM
Alban Lazar1, Gurvan Madec2 and A. J. Busalacchi1
1. ESSIC, University of Maryland, College Park MD
2. LODYC, UMR CNRS, IRD, Univ. Paris VI, Paris, France
Corresponding Author: Dr Alban Lazar
ESSIC, 2207 Computer and Space Science Building,
Univ. Maryland, College Park, MD 20742-2465
Email: alban.lazar@gsfc.nasa.gov
ABSTRACT
We examine the physics of the oceanic meridional transport of heat
by the subtropical gyre HGY in an idealized OGCM. The contribution of the
gyre to the net mid-latitude heat transport H is important to understand
because, unlike sometimes considered, it can be significant compared to
the meridional overturning circulation. Therefore it is useful to gain
a better appreciation of it, in order eventually to improve the simulation
of the total heat transport. This work points out the sensitivity of HGY
to three properties of the model: the physics of the surface heat flux
through the value of the relaxation time constant, the physics of the mixed
layer through its depth, and the parameterization of lateral diffusion
through the intensity of the diffusion coefficient.
The analysis shows that the larger the relaxation time constant, the
larger the gyre contribution. Simultaneously, the contribution of the meridional
overturning circulation increases, but the net effect is positive for the
total heat transport. Nevertheless, recent estimate from observations suggest
a smaller relaxation time constant, which would produce a smaller gyre
contribution. Given a value for this constant, we argue that a deeper mixed
layer, a higher HGY. This mechanism is used to explain important differences
between previous idealized studies of the physics of H. At last, we show
that the lower the intensity of the lateral diffusivity in various parameterizations
of meso-scale processes, the larger the heat transport contribution of
the gyre. This substantial modification of the physics of H is systematically
accompanied by a decrease in the contribution of the diffusive term and
various impact on that of the meridional overturning. The net impact on
H is therefore not systematic. We only obtained a net increase in H for
a weak relaxation time constant, and the opposite otherwise.