Geoscience Reference
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Fig. 2.7 Average σ 0 profile(solid)fromthelast3hbeforethepoweroutageonday76andthefirst
3h after power was restored on day 79 (limitsindicated by shading). The symbols mark σ 0 values
at the lowest cluster on theturbulence mast (17.7m) at timesindicated. The dashed lineshows the
difference in isopyncnal elevation between conditions observed at time 78.5 and the undisturbed
surrounding ocean
During the 3-h period centered at 1200 UT, measured turbulent heat flux was 150
and 460Wm 2 at 5.7 and 9.7m, respectively. The latter was more than an order
of magnitude greater than observed at any other time during the nearly year-long
deployment.
Theobservedresponsewaspuzzling.Therehadbeenanepisodeofpressureridge
building about 110m “upstream” of the turbulence mast just before the March 19
event, which could have conceivably caused a “wake” that would raise the pycn-
ocline; however, we had not witnessed anything similar from flow across pressure
ridges before (or after) during SHEBA. Application of a “large-eddy-simulation”
model that would have resolved small enough scales to simulate the impact of a
pressure ridge keel was unable to reproduce the observed upwelling (Skyllingstad
etal.2003).Sincetheincreaseinpotentialenergyassociatedwiththeriseinthepy-
cnoclinewasappreciable,itseemedunlikelythatturbulentmixingalonecouldhave
accounted for the change, and as we drifted in response to the wind, the anomaly
revertedto ambientinaboutthe sameamountoftimethatitformed.
AcluetotheoriginoftheMarch19eventcamewithpost-projectanalysisofthe
synthetic aperture radar (SAR) imagery using the automated RGPS system (Kwok
1998).BytrackingfeaturesinsuccessiveSARimagesRGPSprovidedclosetodaily
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