LOCAL ADVECTION PROCESSES IN THE SURFACE-LAYER OF THE MARGINAL ICE-ZONE

Micro-scale turbulent transport processes over the marginal ice zone have been studied by use of a two-dimensional numerical model. It has been found that internal boundary layers (IBLs) of horizontal mean velocity, temperature, and specific humidity reveal a near field and a far field. In the near field, the change in surface roughness dominates the height and growth rate of a velocity IBL. The change in surface heat flux governs the near field of a temperature and humidity IBL. In the far field, approximately x/\L*2\approximately 20, where L*2 is the downstream Obukhov length, the downstream stratification more and more influences the growth rate of IBLs basically by modifying the eddy viscosity. Above more complex terrain consisting of an ensemble of ice strips and leads, a merging height h(M) develops, below which the horizontal variability of the surface modification is clearly observed; h(M) varies with the length scale L of surface modification approximately in proportion to h(M)\L approximately1/20 - 1/10, as a rule of thumb. Above the merging height, an eveloping IBL exists, whose growth depends on the ice cover, i.e., on the integral of surface modification, but changes very little with L. Local advection of mementum, heat, and moisture clearly affects the local surface heat fluxes. Sensible and latent heat fluxes are found to show also a near and far field. However, if areally averaged surface fluxes are to be deduced from grid-averaged flow variables, then details of local advection can be neglected to a reasonably good approximation.