1. AWACS Physical Oceanography: High-Resolution Surveys of the Shelfbreak Front
Glen Gawarkiewicz
Andrey Shcherbina
Frank Bahr
Craig Marquette
Physical Oceanography Department, WHOI
Phil Abbot, OASIS Inc. AWACS Team Leader
Jim Lynch, AOPE, WHOI, Chief Scientist

2. Objectives
Regular mapping of Shelfbreak region with towed Scanfish to determine processes and scales of alongshelf variability
Adaptive sampling of Shelfbreak front to determine interesting features to explore for sound propagation (P. Abbot- OMAS)
Moorings near shelfbreak for temporal variability in shelfbreak front

3. Preliminary Ocean Sampling Plans for AWACS/SW06
Glider, Scanfish Track and HU Low-Res Model
Initial Plans-
Scanfish focuses
On alongshelf,
Gliders focus on
Cross-shelf
sampling G5
Harvard Box (100kmx100km) G1 G2 G3 G4
Scanfish
Track G6

4. Regular Sampling Grid Alongshelf Grid- 30 km alongshelf
At the 60 m, 70 m, 80 m, 100 m,
and 1000 m isobaths
Repeated sections along 80 m multiple times
in some grids
Cross-shelf Grid km
Generally between 80 m and
1000 m isobaths
Needed to resolve Shelfbreak Jet
as alongshelf lines not possible
near jet

5. Adaptive Sampling Embedded within regular grid
Initially- alongshelf features along 80 m
Centered on front at 40 m (OMAS)
Maximum bearings at a single point
Streamwise sampling (3 sections along frontal orientation)
Initial plan- REMUS, had to use Scanfish due to weather

6. Alongshelf Variability- Frontal Meanders and Saline Intrusions
Temperature
Along 80 m
Isobath
August 25
Temperature
along 100 m
isobath
August 25
Salinity along
100 m isobath
August 25
Salinity along
80 m isobath
August 25

7. Offshore Forcing- Strong Ring
Ship ADCP
August 25
0.58 m/s
Maximum
Offshore flow
NW corner
Along 1000 m- salinities
as high as 36.2 PSU
Ship ADCP
August 30
0.58 m/s
Maximum
Onshore
Flow SE
corner

8. Shelfbreak Frontal Structure
Temperature
August 27
Western line
(Along cross-shelf
Mooring line)
Salinity
August 27
Note low salinity
Surface layer
(Hudson outflow)
Density showing buoyant
Surface plume in front

9. Response to Ernesto Salinity September 3 Again, note cross-shelf
gradients in surface
mixed layer
Geostrophic adjustment
within upper layer
Temperature September 3
Note cross-shelf gradients
In surface mixed-layer
Very strong pycnocline at
25 m depth

10. Harvard U. Modelling
Fig 1. Two-way nested modeling domains (1km and 3km res.), overlaid on bathymetry (m) and SW06 mooring positions.
Bathymetry based on NOAA coastal soundings combined with Smith&Sandwell
Fig 2. Barotropic Tidal velocities (u and v) at 39N and 73W, from August 31 to September , as estimated by a new Harvard-OTIS inversion (Matlab code). This variability impacts internal tides/waves.

11. Fig. 3. Horizontal temperature maps in the nested 3km SW06 (top) and 1km AWACS (bottom) modeling domains, on Aug 24, 2006 (left), prior to the Tropical Storm Ernesto, and on Sep 3, 2006 (right), after Tropical Storm Ernesto. The temperature fields shown are at different depths: surface (0m) estimates are shown in the large SW06 domain, while thermocline (30m) estimates are shown in the AWACS domain (bottom).

12. Scientific Problems/Papers
Alongshelf Variability- Saline Intrusions (Glenn, D. Gong, Rutgers- Glider)
Response of Shelfbreak Front to TS Ernesto- Adjustment of mixed-layer gradients and motion of foot of front (P. Lermusiaux, MIT)
Adaptive sampling of frontal features and impact on acoustic propagation (Abbot and Lynch)
Effects of Alongshelf Variability on Internal Wave propagation (T. Duda- Moorings)