HR: 1340h
AN: OS13A-0508    [Abstracts]
TI: Near-Field Frontal Observations From a High-Volume River Plume
AU: * Orton, P M
EM: orton@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Jay, D A
EM: djay@ebs.ogi.edu
AF: OGI School of Science and Engineering, Oregon Health and Science University, 20000 NW Walker Rd, Beaverton, OR 97006 United States
AB: We present observations of very strong convergence, vertical velocities, mixing and bottom boundary layer impacts associated with the leading edge front of the tidally-pulsed Columbia River plume. During four successive greater-ebb spring tides in May 2001, with typical summertime upwelling-favorable winds and riverflow (4900 m$^{3}$ s$^{-1}$), shipboard and helicopter-derived front tracking maps show front propagation patterns similar to those generally seen in Synthetic Aperture Radar (SAR) observations. Shipboard observations during the latter part of ebb tide (5 to 8 h past high water) are consistent with an inertial force balance and a rotary, bore-like vertical circulation. Downwelling velocities are 5-35 cm s$^{-1}$, extending down to the bed below the frontline, reaching our deepest measurements of 70 m. Based on comparisons between oceanic and plume T-S diagrams, the mixing layer extends down to an average depth of 18 m in the region from 50-400 m behind the frontline. We estimate mean mixing parameters over this distance and depth using instability length-scales in $\sim$200 CTD density profiles (a "Thorpe scale" analysis). The mean dissipation, eddy diffusivity, and Thorpe overturn scale are 2 x 10$^{-4}$ W kg$^{-1}$, 6 x 10$^{-2}$ m$^{2}$ s$^{-1}$ and 0.79 m respectively, and decrease with distance behind the front. These observations corroborate the conclusion, from prior laboratory studies and observations of low-volume river plumes, that the leading-edge front plays a dominant role in the flux of buoyancy and other constituents between ocean and plume.
UR: http://www.ldeo.columbia.edu/$\sim$orton/
DE: 4219 Continental shelf processes
DE: 4524 Fine structure and microstructure
DE: 4528 Fronts and jets
DE: 4546 Nearshore processes
DE: 4568 Turbulence, diffusion, and mixing processes
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting