Lerczak, J.1, R. Schlitz2, S. Lentz1, and R. Beardsley1
1Physical Oceanography Department, Woods Hole Oceanographic
Institution, Woods Hole, MA 02543
2National Marine Fisheries Service, Woods Hole, MA 02543
We study the temporally-varying structure of the sub-tidal
currents and stratification on the southern flank of
Georges Bank in the vicinity of the tidal mixing
front (TMF) using hydrographic surveys, meteorological
data, and a moored instrument array deployed on the southern
flank of Georges Bank for 160 days during the spring and summer of 1999.
The array spanned the 60-m isobath (the typical summer
location of the TMF) and covered a cross-bank distance of about 16 km.
Seven moorings were deployed, each with a bottom-mounted acoustic
Doppler current profiler and bottom pressure, temperature, and
conductivity sensors. Three of the moorings were also equipped
with 14 temperature sensors spanning the water column.
This allows for an investigation of the temporal and
spatial evolution of the TMF at unprecedented detail.
In this talk, we describe the challenges of identifying the
TMF in the array measurements. It is likely that the TMF's
position shifts considerably in relation to the location
of the mooring array during the period of the deployment.
We use the cross-bank gradient of stratification
to identify when the TMF is centered on the array location.
When the inner-bank moorings are weakly stratified and the
off-bank moorings are strongly stratified in the summer,
a sharp, sub-tidal, along-bank jet is apparent (25 m below
the surface, width ~ 8 km, maximum currents ~ 30 cm/s). The
cross-bank currents are two-layer on either side of the jet,
and three-layers at the location of the jet. Maximum
cross-bank currents are about 5 cm/s.
A powerpoint version and an html version of this presentation are available on-line.