Fall AGU Meeting (Dec. 2002) COAST abstracts:

• Allen
  
• Bane et al.
  
• Barth et al.
  
• Carney et al.
  
• Couch et al.
  
• Cowles et al.
  
• Dale et al.
  
• Durski et al.
  
• Egbert et al.
  
• Gan et al.
  
• Hales et al.
  
• Kosro et al.
  
• Kuebel et al.
  
• Kurapov et al.
  
• Perlin et al.
  
• Pierce et al.
  
• Ruttenberg et al.
  
• Samelson
  
• Spitz et al.
  
• Wheeler
  

Abstracts should be cited as:

EOS Trans. AGU, 83 (47),
Fall Meet. Suppl.,
Abstract XXXXX-XX, 2002

OS61D-04

Bottom Boundary Layer Behavior during COAST

A Perlin, J N Moum, and J M Klymak

Rapidly-repeated transects of currents, and density and turbulence
through the bottom boundary layer across a relatively uniform
stretch of the continental shelf off Oregon reveal the response
of the bottom boundary layer to a sequence of strong upwelling
followed by relaxation and thence a resumption of upwelling. Dense,
near-bottom fluid was observed to move upslope with upwelling and
back down the slope with relaxation from upwelling. By tracking
the intersection of near-bottom isopycnals with the bottom over
successive transects, we estimate the cross-shore speed of fluid in
the bottom boundary layer. This agrees well with simple estimates
of bottom Ekman velocity from alongshore currents. Modifications to
both the Ekman velocity due to buoyancy forcing and to the speed at
which locations of isopycnal intersection with the bottom move down
the slope due to turbulent mixing improve agreement, but they are
small. Boundary layer thickness is greater during the relaxation from
upwelling and turbulence in the bottom boundary layer is more intense
at this time. Evidence exists for convectively-driven mixing in the
bottom boundary layer during the relaxation. This is presumably
forced by the downslope movement of lighter bottom fluid beneath
dense fluid. During upwelling, fluid in the bottom boundary layer
which has been drawn up the slope is observed to become isolated from
its downslope source. It is argued that this is due to divergence
of the Ekman bottom flow beneath a cross-shore varying current. TS
properties of this water are similar to TS properties of isolated
dense pool observed 90 km further south over the broader shelf, and
it appears that the water is connected all the way along the coast.