AWACS Physical Oceanography: High-Resolution Surveys of the Shelfbreak Front

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 Cross-shelf Grid- 25-35 km Generally between 80 m and 1000 m isobaths Needed to resolve Shelfbreak Jet as alongshelf lines not possible near jet 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

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 100 m isobath August 25 Temperature Along 80 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 11 2006, 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)