Air-Sea Ice Fluxes

Some of my latest work has been involved with model algorithms for the calculation of turbulent fluxes between the atmosphere and sea ice. These algorithms are very similar to those that are used over open ocean except that the surface roughness does not change. It is known, however, that the roughness of sea ice varies according to the type and age of the ice (e.g., Overland 1985; Guest and Davidson 1991). Also, sea ice is not homogeneous, and the presence of snow, ridges, leads (areas of open water between ice floes), and melt ponds in summer affect the surface roughness. We recently compared the observed roughness during a yearlong campaign in the Arctic to the constants used in several model algorithms. For momentum at least, the observed surface roughness is definitely not constant. For heat, it can still be considered a constant, because of the large scatter in the observed roughness (Brunke et al. 2006).

In addition, the atmosphere is usually very stable over sea ice, conditions for which these schemes are largely untested for. In fact, some of these algorithms are particularly problematic for sensible heat flux under very stable conditions. Also, all algorithms produced lower sensible heat fluxes than observed during the summer (Brunke et al. 2006). This is possibly due to the inhomogeneous surface of the sea ice during this time, and the average surface temperature of the various surfaces (ice, melt ponds, and leads) should be used instead of just purely the ice surface temperature as suggested by Andreas et al. (2004).

For more information on this research, check out:

Brunke, M. A., M. Zhou, X. Zeng, and E. L Andreas, 2006: An intercomparison of bulk aerodynamic algorithms used over sea ice with data from the Surface Heat Budget for the Arctic Ocean (SHEBA) experiment. Journal of Geophysical Research, 111, 10.1029/2005JC002907. [View]

The average sensible heat flux as a function of boundary layer stability index (the bulk Richardson number, Ri_b) for the field program Surface Heat and Energy Balance of the Arctic (SHEBA). Shown are those observed as well as those calculated by several model parameterizations. Most models produce sensible heat fluxes within observational error as demarcated by the vertical bars except for very stable conditions (high positive Ri_{b_.}

References

Andreas, E. L, R. E. Jordan, P. S. Guest, P. O. G. Persson, A. A. Grachev, and C. W. Fairall, 2004: Roughness lengths over snow. Preprint CD-ROM, 18th Conference on Hydrology, Seattle, WA, Amer. Meteor. Soc., 8 pp.

Guest, P. S., and K. L. Davidson, 1991: The aerodynamic roughness of different types of sea ice. Journal of Geophysical Research, 96 (C3), 4709-4721.

Overland, J. E., 1985: Atmospheric boundary layer structure and drag coefficients over sea ice. Journal of Geophysical Research, 90, 9029-9049.