The proposed work will assess the dissipation in mesoscale eddies at the western boundary of the Atlantic, where westward propagating eddies and Rossby waves disappear from satellite observations (Zhai et al., 2010). Observations from the RAPID array suggest that eddies and Rossby waves undergo dissipation or conversion to higher modes at the western boundary, but are insufficient to isolate the mechanisms responsible. The planned work will measure the circulation and mixing at the boundary, with a small-boat component and cost-effective enhancement of the RAPID mooring array presently deployed at the site. We expect these measurements will yield unprecedented insight into the processes responsible for dissipating mesoscale eddies.
The work is divided into three main components.
(1) Small-boat expeditions using microstructure profilers and expendable current profilers are planned to make subsurface measurements of two types of eddies: anticyclones and cyclones, at their peak and tail end. Eddy arrival at the boundary can be predicted approximately 80-100 days in advance by using satellite altimetry. Since this is not early enough to schedule NERCs larger research vessels, we plan for this part of the work to be carried out on small vessels hired locally. Given the proximity of the study location to shore (25-60 km off of Abaco, Bahamas), this is achievable with the capabilities of smaller vessels.
(2) Seaglider deployment. Standard seagliders will be used to determine the evolution of eddies and their decay, over their lifecycle at the boundary (~3 months). We propose a pair of Seagliders to be deployed and recovered during the small-boat expeditions. Following the successful execution of the OSMOSIS project, we request two gliders to profile simultaneously for each of two 3-month missions.
(3) Mooring enhancements on RAPID. To put the two eddy "snapshots" in context of longer term variability, we propose to enhance the WB1 mooring on RAPID (26.501 deg N, 76.816 deg W in 1400 m of water) with 24 thermistors and 2 x 75 kHz ADCP at the bottom and middle, upward looking.