Geoscience Reference
In-Depth Information
Site OT−I, 345.750 to 360.250
Site OT−II, 362.625 to 367.500
-
1
-
1
-
2
-
2
z
0
= 12.4 cm
-
3
-
3
z
0
= 4.0 cm
-
4
-
4
-
5
-
5
z
0
= 0.3 cm
-
6
-
6
z
0
= 0.1 cm
-
7
-
7
8
8
-
-
-
9
-
9
2
4
6
1
3
Distance from ice, m
Distance from ice, m
Fig. 9.9
Median values of log
(
z
0
)
for the main ISPOL turbulence mast site in December 2004.
Squares are from a mixing length method (McPhee 2002); circles are application of the LOW.
Error bars are 95% confidence limits(Adapted from McPhee 2008)
06ms
−
1
. Each of these profiles was nondimension-
alized by dividing the complex (vector) current at 2m sampling intervals by the
complex current at 30m. The dimensionless current hodograph then produced a
smoothspiralshapewithabout15
◦
ofcounterclockwiserotationasdepthincreased
from10to30m(McPhee2008,in press).
We reasonedthat an estimate of overallsurface roughnessthat was independent
of the turbulence measurements and perhaps free from local topographic effects
couldbemadeasfollows.First,specifyatrialvaluefor
z
0
.Next,foreachacceptable
currentprofile,usetheSLTCmodeltocalculatethecurrentprofile.Thiswasdoneby
(i)specifyingupperocean
T
and
S
profiles,byinterpolatingintimefromtwicedaily
shipCTDstations;and(ii)forcingthemodeltomatchthemeasuredcurrentat20m,
chosen to be generally in the well mixed layer, but deep enough to be away from
theimmediateimpactofridgekeels.SincetheobjectistoavoidusingTICdata,for
anyparticularmodelrun,
u
∗
0
isfirstestimatedfromaRossby-similaritycalculation,
then adjusted iteratively until the model (relative to ice) velocity matches the ADP
velocityat20m.Wedidthisforthreedifferentvaluesof
z
0
,overtherangeofmedian
valuesshowninFig.9.9.Foreach3-hmodelrun(of43total),themodeledcurrents
were nondimensionalizedby themodel30m current(in a referenceframeattached
to the ice), then averaged. Results (Fig. 9.10) indicate that turning between 10 and
30m was best modeled with
z
0
equal to approximately 4cm, the value found for
4m TIC at the main OT-I site. This not only confirmed that the floe was relatively
rough,butalso provideda way of estimating the totalfloe-averageocean/ice fluxes
ofmomentum,heat,andsaltduringtheentireISPOLproject.
was greater than or equal to 0
.
