Jinlun Zhang
Polar Science Center, APL/UW, Seattle, WA 98105-6698
July 1998
Using data from the 1975 Arctic Ice Dynamics Joint Experiment (AIDJEX), the study of Maykut and McPhee (1995) shows considerable seasonal and spatial variations in the mixed layer depth and in the oceanic heat flux in the Arctic Ocean. However, most ice-ocean models including PIPS 2.0 do not include a mixed layer parameterization or calculation. The mixed layer in these models is simply set to be a slab with a fixed depth everywhere in the model domain. Usually the mixed layer is taken to be the first level of the ocean model. In these ice-ocean models, therefore, there are no seasonal and spatial variations in mixed layer evolution.
From observations and from a physical viewpoint, there is no question that it is necessary to incorporate a mixed layer model into a general circulation ice-ocean model. The question then is: Does a mixed layer model make a difference? To answer this question, Zhang (1993) imbedded the mixed layer model of Kraus and Turner (1967) into a coupled ice-ocean model for the Arctic and GIN seas (also see Zhang et al., 1998). A study with the ice-ocean-mixed-layer model found that there are considerable variations in the mixed layer depth seasonally and spatially. For example, the behavior of mixed layer evolution in the GIN Sea is very different from that in the Arctic Basin. The incorporated mixed layer model does make a difference in calculating the oceanic heat flux, the surface buoyancy flux, and the ice thickness. The impact of a mixed layer model is particularly noticeable at ice edges in marginal ice zones. In particular, the study found that the mixed layer model improves to some extent the prediction of ice edges in the Greenland and Barents seas.
The CPU time consumed in computing a Kraus and Turner mixed layer model was found to be negligibly small compared to that consumed in computing the ocean model. Therefore, it is useful and practical to incorporate such a mixed layer model into ice-ocean models.
References
Kraus, E. B., and J. S. Turner, Tellus, 19, 98-106, 1967.
Maykut, G. A., and M. G. McPhee, J. Geophys. Res., 100, 24,691-24,703, 1995
Hibler, W. D. III, J. Physi. Oceanogr., 9, 815-846, 1979.
Zhang, J., A high resolution ice-ocean model with imbedded mixed layer, Ph.D. Thesis, Dartmouth College, 1993.
Zhang, J., W. D. Hibler III, M. Steele, and D. A. Rothrock, J. Physi. Oceanogr., 28, 191-217, 1998.