Impact of Sea-Ice Bottom Topography on the Ekman Pumping - Towards an Interdisciplinary Approach in Earth System Science - page 132

Fig. 3 Values of the oceanic drag coef cients c w calculated for the Central Arctic. The red line
represents the mean value

With this information we can calculate the drag coef cients for each pro le. The

results are shown in Fig. 3 .
Only a few measurements of oceanic drag coef

cients are available for com-
paring the results obtained with Eqs. 2 and 3 . Lu et al. ( 2011 ) showed (see their
Table 1) that oceanic drag coef

10 − 3 .
Our calculated values lie within this range. We stress that the oceanic drag coef-

10 − 3 to even 22

cients can vary from 1 × ×

ficients vary strongly with the sea-ice topography and that the choice of a constant
value used in global circulation models might imply a bias in the estimation of the
momentum exchange between the ice and the ocean.

4 Ekman Pumping

Ekman pumping in the ocean depends on the spatial variation of the stress applied
at the surface. This spatial variation is a consequence of variations in both the
velocity cients. In this section we want to evaluate the

contribution to Ekman pumping that is caused only by variations of the drag
coef

field and the drag coef

cients. We thus set up a very simple experiment. 32 grid cells aligned along y,
each 20 km wide, form a domain of 20 km 640 km. This domain is covered

completely with sea ice (100 % sea-ice cover). The surface and bottom properties of
the ice are varying from one cell to the other, so that the drag coef

×

cients are also
different. In particular, to each grid cell we assign a value for the drag coef cient

that was calculated (see Sect. 3 ) on the basis of real sea-ice topography. We assume