Geoscience Reference
In-Depth Information
Fig. 5.12
Aerial view of LEADEX Lead 3 showing the temporary station and directions of the
prevailing windandapparent current
keep ice in our operating area just about as compact as possible. But finally, she
relented and a kilometer-wide lead opened about 20km south of the base camp
(Fig. 5.12). In many ways this lead was almost ideal, in that its opening coincided
withamoderatebreezefromthenorth,meaningthatouroceanographicinstruments
deployed on the northern “beach” sensed a boundary layer that appeared to be ad-
vecting toward us from the full fetch of the open water/thin ice region extending
perhaps30boundary-layerthicknessesupstream.
Results reported in McPhee (1994), McPhee and Stanton (1996), and Morison
and McPhee (1998) summarize oceanographic aspects of LeadEx. Those particu-
larly focused on turbulence scales are reviewed here. A novel aspect of the TIC
system deployed during LeadEx was the incorporation of a Sea-Bird Electronics
SBE07microstructureconductivity
(
µ
)
C
sensorintooneoftheinstrumentclusters.
Calibration of the open-electrode
C
sensors is much less stable than the standard
SBE04conductivitymeters,whichroutethesampledwaterthroughanannularduct;
however,theirresponseto smallsalinityvariationsin theflowissuperiorto theun-
pumpedSBE4 sensors. The
µ
C
equippedTIC providedcredibleestimatesof salin-
ityflux,hencedirectmeasurementsofbuoyancyflux(almostentirelydependenton
salinity)forthefirst time.
Turbulencemeasurementsat the edgeof lead 3 overabouthalf a day(Fig. 5.13)
show relatively mild stress with
u
∗
about 7mms
−
1
and buoyancy flux of about
−
µ
Wkg
−
1
, which is somewhat less than half in magnitude of the stabilizing
buoyancyfluxdescribedaboveintheMIZEXmeltingexample.ThemeanObukhov
lengthwasabout
0
.
08
µ
4.Themeansalinityfluxovertheperiodshown
in Fig. 5.13 suggests that salt was entering the upper ocean from basal freezing at
−
12mwith
µ
∗
≈−
