Geoscience Reference
In-Depth Information
Average S, 3 to 15 m
30.4
Model
Profiler
a
Run Sep 14A
30.2
30
29.8
29.6
257
258
259
260
261
262
263
264
265
Average
T, 3−15 m
δ
0.04
b
0.03
0.02
0.01
257
258
259
260
261
262
263
264
265
Day of 1998
Fig. 8.9
Wellmixedlayerproperties:
a
salinityand
b
temperature elevationabove freezing. Circle
symbols are 3-h averages of the SHEBAprofiler data; dashed lineis from model run Sep 14A
equivalentto about2cm of ice melt. Asimilar calculationfor
∆
S
in the upper60m
fromthestartingandendingSHEBAsalinityprofilesshowsachangeinsaltcontent
of about
36kgm
−
2
, requiring enough melting (1.7m) to completely eliminate
the ice pack! Another model simulation (run Sep14B) was made in which a small
constantadvectivesourcetermwasspecifiedacrosstheentiremodeldomainateach
timestep:
−
∆
S
(
obs
)
S
=
H
(
t
end
−
t
st art
)
where
∆
S
(
obs
)
is the observed total change in salt content in the upper 60m over
the
∆
S
match the observed value. The model results
forstress arenotmuchdifferentfromrunSep 14A;modeledheatfluxis somewhat
less.Resultsfor
∼
8 days, making the modeled
T
inthewellmixedlayer(Fig.8.11)showaboutthesameoverall
decrease as in the data. The simulation is not meant to be very realistic, given the
temporalchangesevidentinFig.8.10a,butrathertoshowthattheobserveddecrease
in
δ
T
probably resulted from advection instead than local vertical processes. In
effect,theadvectivedecreaseinsalinityasthestationdriftednorthmorethanoffset
theupwardverticalmixingofbothsaltandheatfromthepycnocline.
An important point to be made from this exercise is that in general it is quite
difficult to evaluate the performance of upper ocean models by testing their abil-
ity to simulate short-term changes in mean properties of the upper ocean. Often
δ
