Showing papers by "Kenneth H. Brink published in 1999"

High‐frequency internal waves on a sloping shelf

Abstract: The behavior of an internal wave in a continuously stratified fluid over a sloping bottom is examined by finding approximate analytic solutions for the amplitude of waves in a coastal ocean with constant bottom slope, linear bottom friction, and barotropic mean flows. These solutions are valid for frequencies higher than the frequency of critical reflection from the sloping bottom. The solutions show that internal waves propagating toward the shore are refracted, so that their crests become parallel to shore as they approach the coast, and outward propagating waves are reflected back toward the coast from a caustic. Inviscid solutions predict that the amplitude of a wave goes to infinity at the coast, but these infinite amplitudes are removed by even infinitesimal bottom friction. These solutions for individual rays are then integrated for an ensemble of internal wave rays of random orientation that originate at the shelf break and propagate across the shelf. It is found that for much of the shelf the shape of the current ellipse caused by these waves is nearly independent of the waves' frequency. The orientation of the current ellipse relative to isobaths is controlled by the redness of the internal wave spectrum at the shelf break and the strength of mean currents. Friction is more important on broader shelves, and consequently, on broad shelves the internal wave climate is likely to be dominated by any internal waves generated on the shelf, not waves propagating in from the deep ocean.

Long-term moored observations on Georges Bank as part of the U.S. GLOBEC Northwest Atlantic/Georges Bank program

Abstract: Moored measurements have been made on Georges Bank from fall 1994 to fall 1999 as part of the US GLOBEC Northwest Atlantic/Georges Bank Program. The southern flank mooring was located in 76 m of water between the shelf/slope front, which separates the North Atlantic from Georges Bank, and the tidally well-mixed region over the crest of the bank. The mooring carried a full suite of meteorological sensors and water temperature and conductivity (salinity) sensors at many depths, an Acoustic Doppler Current Profiler to measure currents over much of the water column, and bio-optical sensors to measure biological variables. The temperature and salinity data show great variability on time scales from tidal to inter-annual. Warm-core rings occasionally "bumped" into Georges Bank, and their effects (warm, salty, biologically inactive water) often extend onto the bank. Pulses of Scotian Shelf water (cold and fresh) were observed to move westward along the southern flank. Salinity shows a steady, long-term decrease by greater than one PSU over the first four years of observations with only a small indication of a reversal in 1999. A five-year moored record is a significant achievement, but with the large variability observed in the coastal ocean, longer records are needed to help relate long-term oceanic changes to climate changes.