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SUMMARY:Downwelling in Basins Subject to Buoyancy Loss - Claudia Cenedese 
 (Woods Hole Oceanographic Institution)
DTSTART:20120312T130000Z
DTEND:20120312T140000Z
UID:TALK36892@talks.cam.ac.uk
CONTACT:Doris Allen
DESCRIPTION:Recent observational\, theoretical\, and modeling studies all 
 suggest that the upper part of the downwelling limb of the thermohaline ci
 rculation is concentrated in strong currents subject to buoyancy loss near
  lateral boundaries. This is fundamentally different from the traditional 
 view that downwelling takes place in regions of deep convection. Even when
  resolving the buoyant boundary currents\, coarse resolution global circul
 ation and climate models rely on parameterizations of poorly known turbule
 nt mixing processes. In this study\, the first direct measurements of down
 welling occurring within a basin subject to buoyancy loss are obtained. Do
 wnwelling\nis observed near the basin's vertical wall within the buoyant b
 oundary current flowing cyclonically around the basin. Although the entire
  basin is cooled\, downwelling is absent in the basin interior. Laboratory
  rotating experiments are conducted to explicitly resolve the turbulent mi
 xing due to convective plumes\, the baroclinic eddies generated by the bou
 ndary current\, and identify where downwelling takes place. Hence\, in the
  laboratory small\nvertical velocities can be measured more reliably than 
 in many numerical calculations\, while the measurement of these small vert
 ical velocities is still a challenge for field experiments. Downwelling is
  observed to occur near the vertical wall within a boundary layer with a t
 hickness that scales with the Rossby radius of deformation\, consistent wi
 th the dynamical balance proposed by a previous numerical study. Hence\, d
 ownwelling in the Labrador\nSea and Lofoten Basin cyclonic boundary curren
 ts may be concentrated in a Rossby deformation thick boundary layer in reg
 ions with large eddy generation.
LOCATION:MR14\, Centre for Mathematical Sciences
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