Geoscience Reference
In-Depth Information
5.1.2 Ice Station Polarstern
Asdiscussedpreviously,duringthe2004-2005ISPOLdriftinthewesternWeddell
Sea, we deployed turbulence clusters equipped with ADVOcean current meters in
the upper ocean under a heterogeneousmultiyear ice floe. The ADVs measure ve-
locity by gauging the Doppler shift of scattered sound in a small (approximately
1
2cm) cone separated from the sensors by about 18cm. As long as there are
adequate sound scatterers in the fluid, the current meters have virtually no lower
threshold velocity with little interference from the apparatus. When flow energy is
low, this makes them far superior to the earlier “Smith-rotor” mechanical current
metertripletsformeasuringcurrentcharacteristics.
Overthecourseofthemonth-longturbulence-mastdeployment,severalconfigu-
rationswereutilized,withtwo orthreeTICsatdepthsrangingfrom1to 10mfrom
theice-waterinterface(McPhee2008,inpress).Aswithpreviousanalyses,theTIC
data streams were divided into 15-min realizations, rotated into a streamline refer-
ence frame with covariance statistics and variance spectra calculated for each real-
ization. Smoothed spectral estimates were averaged in evenly spaced log
×
bins,
then further averagedin 3-h blocks. A typicalaverage, area-preserving
w
spectrum
is shown in Fig. 5.6, with a high-order polynomialfit from which the maximum is
determined,asindicatedbythedot-dashedline.
(
k
)
Fig. 5.6
Three-hour average spectrum from ISPOL centered at 0900 UT on 23 December 2004.
The dashed line is a high-order polynomial fit, from which the maximum is determined where the
derivative is zero (From McPhee 2008, in press)
