Geoscience Reference
In-Depth Information
0.1
600
Incoming Shortwave
a
0.09
400
∆
T
0.08
200
0
167
167.5
168
168.5
169
169.5
170
170.5
171
Day of 1998
2
x 10
-
4
4
Mean heat flux
b
0
0
-
2
−4
T/
z
-
∆
∆
-
4
167
167.5
168
168.5
169
169.5
170
170.5
171
Day of 1998
Fig. 8.3 a
Incoming shortwave radiation at the upper ice surface (data from the SHEBA Project
Office installation, right caption) and departure of mast temperature from freezing (average of
clusters1and2at4.2and8.2m,respectively).
b
Negativetemperature gradient betweenclusters1
and 2, after adjusting temperatures to agree at times near zero heat flux, along with turbulent heat
flux averaged for both clusters (see also colorplate on p. 209)
about 1mK).
1
To the degree that the different scale limits in Fig. 8.3b represent
in the same way the variation in
w
T
, their ratio provides a
rough estimate of the mean eddy diffusivity throughout the period, namely about
2
−
∂
T
/
∂
z
and
ρ
c
p
10
−
3
m
2
s
−
1
.
The period from day 167 to 171 (16-20 June 1998) was modeled as follows.
Initiallythetemperatureandsalinityoftheupperoceanweresettovaluesmeasured
bytheSHEBAprofilingCTDusinga3-haveragecenteredattime167.0.Theupper
boundaryconditionformomentumfluxwasspecified(Section7.2.2)fromthetime
seriesoficevelocityafterremovinginertialmotion.Surfaceroughnesswasassigned
a value of 0.048m from the “scaled up” analysis described later in Section 9.3.3.
This is significantly rougher than the estimate for the immediate SHEBA Site 2
roughness (McPhee 2002), but was thought to be more appropriate for modeling
thermalchangesoverthe entire upperocean. For the interface submodel,heat con-
duction in the ice was estimated from the temperature gradient in the lower 50cm
of ice at mass balance station “Pittsburgh,” taken to be fairly representative of the
entirefloe.Overthefour-dayperiod,theaverageupwardheatconductioninthe ice
basedonthisgradientwas
.
5
×
1.9Wm
−
2
.
∼
1
Forverysmallgradients,theadiabaticlapserateinthewellmixedlayerisimportant;however,by
calibrating the thermometers to a time of near zero heat flux, the difference between temperature
and potential temperature has already been taken into account.
