Sb. Power et R. Kleeman, SURFACE HEAT-FLUX PARAMETERIZATION AND THE RESPONSE OF OCEAN GENERAL-CIRCULATION MODELS TO HIGH-LATITUDE FRESHENING, Tellus. Series A, Dynamic meteorology and oceanography, 46(1), 1994, pp. 86-95
A global ocean general circulation model (OGCM) is forced using mixed
boundary conditions (i.e., a restoring condition on the upper level te
mperature but using a fixed, specified surface salt flux). A freshwate
r flux anomaly is then applied over the western half of the sub-polar
gyre in the northern North Atlantic. The response of the model is foun
d to be dependent upon the details of the parameterization of the surf
ace heat flux: In particular the ''coupling strength'' or Haney relaxa
tion time is crucial. Responses range from a halocline catastrophe at
short relaxation times (strong coupling) to a very modest perturbation
at longer relaxation times (weaker coupling). An accurate parameteriz
ation is therefore required to properly model the evolution of the res
ponse. It is uncertain that the restorative condition is sufficiently
realistic, especially in cases where a significantly different climato
logy is obtained. It is possible, for example, that the evolution coul
d move from an unstable trajectory to a stable one if the parameters i
n the heat flux formulation are also allowed to evolve. This might hel
p to explain why OGCMs under mixed boundary conditions are more sensit
ive than the observations suggest they should be. When a recovery does
occur it does so on decadal time scales. It is therefore tempting to
speculate that the positive feedback on the initial perturbation provi
ded by the heat flux response plays a central role in the dynamics of
North Atlantic variability, in a manner that is analogous to the wind-
stress feedback in the El Nino, Southern Oscillation.