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2002 LAPCOD Meeting
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Absolute transports of the North Atlantic Current from RAFOS floats and historical hydrography
Paula Perez-Brunius, Tom Rossby, Randy Watts
University of Rhode Island
pperez@gso.uri.edu(Abstract received 09/29/2002 for session A)
ABSTRACT
The North Atlantic Current (NAC)- Subpolar Front (SPF) current system serves as a conduit of warm salty waters into the northern North Atlantic. It is the upper limb of the thermohaline circulation of the Atlantic ocean, and plays a crucial role in the moderation of European Climate. Its transport and corresponding heat fluxes remain uncertain, mainly because the structure of the system is not well known. We estimate the mean absolute transports of mass and temperature (top 1000 db) for the NAC-SPF region, using a new method that combines isopycnal RAFOS float data with Gravest Empirical Mode (GEM) projections of historical hydrography. The mean absolute transport potential field shows a NAC-SPF ``pipe'', defined by two bounding transport potential contours. This pipe transports 15.0±3.1 Sv (top 1000 db) from the subtropics into the eastern subpolar North Atlantic. The northward flowing NAC follows a distinct meandering path, with no evidence of permanent branches peeling off the current before reaching the Northwest Corner. As the current enters the Northwest Corner, it appears to split into two branches, which together constitute the eastward flowing SPF. The two branches converge to cross the Mid-Atlantic Ridge above the Charlie-Gibbs and Faraday Fracture Zones. We calculate the absolute transport of temperature (top 1000 db) across seven transects crossing the NAC-SPF ``pipe''. Since mass is conserved in the pipe, changes in the temperature transports are due to lateral exchange and mixing across the pipe's side walls, and to air-sea fluxes across the surface of the pipe. The NAC-SPF current loses 0.27±0.06 PW on its transit through the region. This loss is much larger than the corresponding heat lost to the atmosphere. We conclude that cross-frontal exchange induced by the steep meanders of the northward flowing NAC is the main mechanism by which heat is lost along the current. (Detailed description of the float-GEM method presented in poster session).
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2002 LAPCOD Meeting, Key Largo, Florida, December 12-16, 2000