HR: 16:00h
AN: OS52G-07    [PDF]
TI: High Frequency Varability on the New England Shelf during the 2001 CBLAST-Low Pilot Experiment
AU: * Pritchard, M
EM: mp@env.leeds.ac.uk
AF: Department of Physical Oceanography, Woods Hole Oceanographic Institute, Woods Hole, MA 02543 United States
AU: * Pritchard, M
EM: mp@env.leeds.ac.uk
AF: Institute for Atmospheric Science, School of the Environment University of Leeds, Leeds, LS2 9JT United Kingdom
AU: Weller, R A
EM: rweller@whoi.edu
AF: Department of Physical Oceanography, Woods Hole Oceanographic Institute, Woods Hole, MA 02543 United States
AB: During July-August 2001, ship surveys and 2-surface ASIMET and subsurface moorings were deployed south of Martha's Vineyard, MA on the New England Shelf as part of the CBLAST-Low (Coupled Boundary Layer Air-Sea Transfer under Low wind conditions) pilot experiment. For approximately 30-days, meteorological and sub-surface instrumentation at onshore and offshore mooring sites recorded high frequency time series data through synoptic weather conditions. Across shelf CTD sections showed strong vertically stratified waters associated with the onshore encroachment of a cooler lower layer driven by upwelling favourable wind stress. Estimates of thermal wind shear calculated from these CTD surveys suggested surface waters were driven in a westerly direction due to on-off shelf horizontal temperature gradients. High frequency subsurface measurements of pressure, temperature, salinity and velocity recorded internal wave signatures and the presence of solitons coinciding with the onshore propagation of the internal tide. Observations at the inshore mooring site and an internal wave breaking criterion derived in earlier laboratory studies suggested that soliton wave packets were shoaling and forming a bottom bore on the flood phase of the tide. The internal bores were further enhanced during the ebb when the breaking waves coalesce with offshore run back from a gravitationally unstable flow formed during a previous shoaling event. The bores undular trailing wave crests could also be observed in aircraft remote sensing imagery through enhanced vertical velocities associated with the wave coalescence. The stability and mixing of the bores is quantified through a 2-layer Froude number hydraulic control criterion and the observed potential energy anomalies of the water column. The inference of these periodic features on mixing in this inner shelf region at supra-tidal and semi-diurnal time scales are discussed.
DE: 4219 Continental shelf processes
DE: 4504 Air/sea interactions (0312)
DE: 4544 Internal and inertial waves
SC: Ocean Sciences [OS]
MN: 2004 Ocean Sciences Meeting