Geoscience Reference
In-Depth Information
0.02
a
0.2
u
*0
0.01
0.1
∆
T
0
0
232
234
236
238
240
242
244
246
248
250
-
0.35
0
-
0.4
h
ice
-
0.45
−0.02
-
0.5
−0.04
b
<w
b
>
*0
-
0.55
232
234
236
238
240
242
244
246
248
250
Day of 2005
Fig. 8.20 a
PDModelinterfacefrictionvelocity(dashed)anddepartureofmixedlayertemperature
from freezing (shaded);
b
ice draft (shaded) and interface buoyancy flux (dashed) for an IOBL
model where all density gradients are based on potential density. (see also colorplate on p. 211)
In the modeling examples described below, the intent is not to faithfully pre-
dicttheevolutionofupperoceanstructureatstation 91fortheentire20-dayperiod
(whichisunknown),butrathertoexploreramificationsofmixinginalowstaticsta-
bilityenvironment.Tothatend,themodelwasrunfirstwithallofthebuoyancyflux
dependent parameters calculated from gradients in potential density, and with no
mixing (beyond molecular) below the IOBL extent, which was determined by dy-
namicconditionsatthesurfacealongwithmodeledchangesin thetemperatureand
salinity profiles. This model is designated PD (indicating that gradients depend on
potential density) and its results are summarized in Fig. 8.20. Parameters that gov-
ernbasalheatflux(frictionvelocityandelevationofmixedlayertemperatureabove
freezing)showthatinthesecondpartoftheperiod,higher
T
issomewhatcompen-
satedbylower
u
∗
0
andlowerairtemperature,sothatuntiltheveryendoftheperiod,
icecontinuesto growasits upwardheatconduction(plussmallloss in openwater)
exceedsheat flux from the ocean. Total ice growth of about12cm supplies a small
but nearly continuous negative buoyancy flux (dashed curve in Fig. 8.20b, mean
value
∆
10
−
8
Wkg
−
3
). In the PD model, this contributes to turbulence in the
IOBLandaslowdeepeningofthethermocline(Fig.8.21).Forthemostpart,thedy-
namicIOBLdepth(whitedashedcurveinFig.8.21,definedhereasthedepthbelow
which
u
∗
<
−
2
×
10
−
3
ms
−
1
)followsthethermoclineclosely.Asupperlayersalin-
ity increases from the downward salt flux, the pycnocline weakens, until on about
day243,iterodesenoughofthethermoclinetocauseanoticeabletemperaturespike
0
.
5
×
