Figure 11. Neutral-stability, 10-m air
ice drag coefficients computed from
eq 111 using snow-surface elevation
profiles collected during the Winter
Weddell Gyre Study (Andreas et al.
1993b).
The power of eq 111 is its implicit suggestion that it
puted for each ice class. Because WWGS scientists had
may be possible to determine the drag coefficient re-
little opportunity to sample second-year floes, the sta-
motely from instruments sensitive to surface roughness.
tistics on classes III and IV in the figure are uncertain.
In this light, eq 111 warranted further investigation. The
But for classes I and II, where the sample size is larger,
Winter Weddell Gyre Study (WWGS; Augstein et al.
Figure 11 corroborates our earlier speculation: When
1991) on the Polarstern gave us an opportunity to try
the ice is identifiably rougher (i.e., deformed), the drag
this inverse use of eq 111. During a 1989 transect of
coefficient is generally larger.
the Weddell Sea, WWGS scientists collected 47 snow-
Much of the appeal of eq 111 is the unification it
surface profiles like that in Figure 9, except most were
provides; it confirms our intuition about the importance
only about 100 m long. We computed Φs from these,
of roughness on drag with hard data. Unfortunately, no
then ξ from eq 112, and finally CDN10 from eq 111 (An-
one has found independent confirmation of eq 111 (e.g.,
dreas et al. 1993b). Figure 11 shows a histogram of the
Shirasawa 1981). The actual form of eq 111 may be a
resulting values.
moot point, however. Our recent observations on Ice
Lange and Eichen (1991) had developed a classifi-
Station Weddell in the western Weddell Sea imply that
cation scheme for sea ice in the Weddell Sea. They iden-
eq 111 oversimplifies airice coupling.
Figure 12 is a time series of ISW CDN10 values that
tified four ice classes, as follows:
Class I: deformed first-year ice
Andreas and Claffey (1995) deduced from four-level
Class II: undeformed first-year ice
wind speed profiles, including those in Figure 3. Though
ce Stat o
edde
Class III: undeformed second-year (multiyear) ice
3.0
Class IV: deformed second-year (multiyear) ice
In Figure 11, I distinguish the drag coefficients com-
2.5
2.0
1.5
Figure 12. Time series of the neutral-stability, 10-m
drag coefficient measured on a fixed mast on Ice
1.0
Station Weddell (see Andreas and Claffey [1995] or
62
67
72
77
82
87
92
Andreas [1995a]).
Julian Day
18
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