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Fig. 6.9 Upper panel: bottom elevation of “false bottom” thickness gauges relative to their read-
ings on day 190. Box marks the ten-day period chosen for simulation. Bottom panel: Interface
frictionvelocitydetermined from icedrift relative togeostrophic current, for twovalues of surface
roughness spanning range of estimates for AIDJEX station Big Bear (Adapted from Notz et al.
2003. Withpermission American Geophysical Union) (see also Colorplate on p. 206)
bulk Stanton number (6.10) be 0.0057, the mean SHEBA value, and z 0 =
6mm,
assuming the area around the false bottoms would be similar to the undeformed
multiyeariceobservedduringSHEBA(McPhee2002).
Modelresultsforthickiceshowabout6cmofbottomablationoverthetendays
(Fig. 6.10a), compared with about 14cm of upward migration of the modeled
false bottom (Fig. 6.10b). In each case the model matches Hanson's observations
pretty well. The combination of
α h =
0
.
0111 and
α h / α S =
50 (which provides
St =
.
0057,seeFig. 6.6)waschosenas thecombinationthatminimizedthe root-
mean square error between the model and observations in Fig. 6.10b, for R in the
range 35 to 70. If the model is run with R
0
=
=
.
1, with
α
0
0058 (to maintain
h
St =
0057) the results are reasonable for thick ice (Fig. 6.11a) but nonsensical
for false bottom migration (Fig. 6.11b). The persistence of false bottoms in the
summerpackisthusdifficulttoexplainwithoutinvokingfairlystrongdoublediffu-
sion.
InFig.6.12a,modeledupwardheatexchangebetweentheoceanandthickiceis
comparedwith the downwardheat flux from false bottomsfor the double-diffusive
regime of Fig. 6.10. Because of the relatively large positive temperature gradient
0
.
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