Showing papers by "Kenneth H. Brink published in 1989"

The effect of stratification on seamount-trapped waves

Abstract: Circular, isolated seamounts can support the propagation of an infinite set of trapped waves. These waves exist at discrete subinertial frequencies and azimuthal wavenumbers. The wave frequencies increase as the height of the seamount or the stratification increases. Idealized examples demonstrate these trends, as well as the tendency for bottom-trapping of the velocity field to increase as stratification increases. Bottom frictional effects are weak enough that at least the simpler (graver) wave modes should last several periods before significant damping occurs. The waves should be most observable as current variations, although associated temperature fluctuations also may be measurable.

Evidence for wind‐driven current fluctuations in the western North Atlantic

Abstract: Two subsurface current meter moorings were deployed for 20 months along 70°W in a low-energy portion of the western North Atlantic. The resulting data were compared with estimates of the wind stress curl in an attempt to seek a relationship between currents below the mixed layer and meteorological forcing at subinertial frequencies. Currents and temperature tend to be significantly coherent with the curl and are most coherent with the curl at remote locations, usually more than 500 km away from the mooring and generally to the east. Coherences generally decrease with increasing frequency. The current response is surface intensified. A linear stratified model for stochastically wind-forced Rossby waves in a flat-bottomed ocean is presented as an attempt to rationalize the results. The effort was not entirely successful, so that it appears that a more realistic model, perhaps including bottom topography and mean currents, will be needed to rationalize these observations fully.

Observations of the Response of Thermocline Currents to a Hurricane

Abstract: In September 1985, the eye of Hurricane Gloria passed within about 100 km of a current meter mooring in the western North Atlantic. Data from this mooring provide a clear view of the vertical structure of the near-inertial wake in the main thermocline. The response at 159 m was strong (>25 cm s−1 amplitude) and lasted about 18 days. At greater depths, the response was weaker and more irregular. The phase of the near-inertial currents increased with depth, consistent with the downward spreading of enemy. The total phase change across the thermocline reached about a half cycle seven days after the hurricane's passage, indicating a large vertical scale of the response. The observations are briefly compared with other time series measurements (on the continental margin) and with models.

Topographic Stress in Coastal Circulation Dynamics

Abstract: The interaction of nonlinear shelf waves or eddies with longshore variation of topography is addressed. The dynamics are subtle and, perhaps for this reason, have been largely overlooked. Our own results are preliminary; but they point toward an unexpectedly strong influence such that, in many coastal environments, topographic stress may overwhelm other forces. The topographic stress acts to drive undercurrents in the sense of intrinsic shelf wave propagation, hence poleward on eastern boundaries. Potentially, a very important consideration is that a secondary circulation associated with this stress has the sense of upwelling on all boundaries in either hemisphere.

Energy Conservation in Coastal-Trapped Wave Calculations

Abstract: A consideration of energy conservation for coastal-trapped waves shows that, for a slowly varying medium, the normalization of the wave modes is not arbitrary. Errors related to incorrect normalization are demonstrated for a simple analytic example and for a realistic case. If alongshore changes in latitude, topography or stratification are substantial, then predicted time series are shown by example to have amplitude errors of as much as 50% if an incorrect normalization is applied.