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Bottom-Following Lagrangian Floats
Mark Prater, Tom Rossby
Graduate School of Oceanography, University of Rhode Island
mprater@gso.uri.edu(Abstract received 04/29/2005 for session C)
ABSTRACT
The majority of the Lagrangian floats used today are designed to follow the flow along two different surfaces: either those of constant pressure (isobaric), or else of constant potential density (isopycnal). However, many oceanographic processes result in flows that follow neither isobaric nor isopycnal (nor even neutral) surfaces. For example, density currents off continental shelves or over inter-basin sills hug the bottom and descend hundreds to thousands of meters, and thus dramatically deviate from an initial isobaric surface. In addition, mixing in the overflow can change the density of the current as lighter ambient waters are entrained and thus can cause the plume to deviate from the initial isopycnal surface. A simple "bottom-following", or constant altitude, RAFOS float was developed to better follow the plume from the Faroe Bank Channel Overflow, and examine the plume from a Lagrangian viewpoint. These floats were deployed at, or downstream, of the the sill and were tracked through the Iceland Basin. The resulting trajectories agreed well with Killworth's idealized plume descent model, and showed evidence of deep mesoscale motions. However, the simplistic technique used to maintain the float's altitude above the bottom had obvious problems, and a new method is proposed. This new type of float will be valuable in studies of overflows and casades, as well as in shallow seas where it is difficult to follow conventional isobaric or isopycnal surfaces.
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2005 LAPCOD Meeting, Lerici, Italy, June 13-17, 2005