Jiayan Yang and J. David Neelin
J. Clim., 10, 3059-3076, 1997.
Paper (PDF 402KB)
© Copyright 1997 by the American Meteorological Society.
Abstract. An interdecadal oscillation in a coupled ocean-ice system was identified in a previous study (Yang and Neelin, 1993). This paper extends that study to further examine the stability of the oscillation and the sensitivity of its frequency to various parameters and forcing fields. Three models are used: (i) an analytical box model, (ii) a two-dimensional model for the ocean thermohaline circulation (THC) coupled to a thermodynamic ice model, as in our previous study, (iii) a three-dimensional ocean general circulation model (OGCM) coupled to a similar ice model. The box-model is used to elucidate the essential feedbacks that give rise to this oscillation and to identify the most important parameters and processes that determine the period. Numerical experiments in the two-dimensional THC-ice model show that the model stability is sensitive to the ocean-ice coupling coefficient, the eddy diffusivity, and the strength of the thermohaline-circulation feedback per unit surface-polar density perturbation. The coupled model becomes more stable toward low coupling, greater diffusion and weaker THC feedback. The period of the oscillation is less sensitive to these parameters. Nonlinear effects in the sea-ice model become important in the higher ocean-ice coupling regime where the effective sea-ice damping associated with this nonlinearity stabilizes the model. Surface Newtonian damping is also tested. The three-dimensional OGCM, which includes both wind stress and buoyancy forcings, is used to test this coupled ocean-ice mechanism in a more realistic model setting. This model generates an interdecadal oscillation whose characteristics and phase relations among the model variables are similar to the oscillation obtained in the 2-dimensional models. The major difference is that the oscillation frequency is considerably lower. This difference can be explained in terms of the analytical box-model solution in which the period of the oscillation depends on the rate of anomalous density production by melting/cooling of sea ice per SST anomaly, times the rate of warming/cooling by anomalous THC heat advection per change in density anomaly. The 3-D model has a smaller THC response to high-latitude density perturbations than in the 2-D model, and anomalous velocities in the 3-D case tend to follow the mean isotherms so the anomalous heat advection is reduced. This slows the ocean-ice feedback process, leading to the longer oscillation period.
Citation. Yang, J.-Y., and J. D. Neelin, 1997: Decadal Variability in Coupled Sea-Ice-Thermohaline Circulation Systems. J. Clim., 10, 3059-3076.
Acknowledgements This work was supported by NOAA Atlantic
Climate Change Program grant NA56GP0209 (JY), National Science Foundation
Grants ATM-9158294 and ATM-9521389 (JDN and JY), a grant from the National
Institute for Global Environmental Change (JDN and JY), and a Mellon
Independent Study Award from the Woods Hole Oceanographic Institution (JY).
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