Showing papers by "Kenneth H. Brink published in 1990"

Coastal-Trapped Waves off the Coast of South Africa: Generation, Propagation and Current Structures

Abstract: Coastal sea level variations from six sites around South Africa are used to establish the characteristics of coastal-trapped wave (CTW) propagation Substantial amplitudes (>50 cm) are found along the south coast, but further propagation on the east coast against the Agulhas Current is inhibited Current measurements over the shelf in this region show barotropic reversals during the passage of the peak of a CTW, with essentially geostrophic flow occurring Comparisons are made with theoretically calculated first-mode CTW characteristics along various sections of the coast These calculated speeds fall within the range of speeds determined from observation, though an admixture of a mode 2 CTW is possible It is found that the speeds of wind systems moving along the coast also fall in the same range, probably leading to a resonance condition, and an explanation for the large CTW amplitudes

On the generation of seamount-trapped waves

Abstract: A model is presented for the excitation, by ambient currents, of subinertial frequency motions over a seamount. Continous density stratification, bottom friction and linear f -plane dynamics are assumed. For the case of a horizontally uniform ambient flow, the first few seamount-trapped wave modes are clearly excited, but more complex (lower frequency) modes are not generated because of frictional damping. For a horizontally-sheared ambient flow, resonances are less obvious, and the low-frequency response is dominated by flow having no azimuthal variations. In all cases, responses are strong enough that it seems likely that seamount-trapped motions often will be observable in nature.

Observations of phytoplankton and nutrients from a Lagrangian drifter off northern California

Abstract: A Lagrangian drifter was deployed in a cold filament off northern California as part of the Coastal Transition Zone program. The drifter was equipped with an optical package (consisting of a spectroradiometer, a fluorometer, and a beam transmissometer) suspended at 8.5-m depth and a water sampler suspended at 16.3-m depth. The drifter was recovered after 8 days. Optical, chemical, and biological properties changed considerably as the drifter moved offshore in the cold filament. Concentrations of phytoplankton chlorophyll increased rapidly in the first 2 days, in parallel with the disappearance of nitrate and nitrite. After this initial period, chlorophyll decreased gradually over the next 6 days with prominent diurnal fluctuations present in the last 3 days. Water transparency also showed similar long-term as well as diurnal fluctuations. The phytoplankton community became increasingly dominated by large centric diatoms throughout the deployment. Although total cell volume was higher towards the middle of the deployment, this increase occurred without a parallel increase in chlorophyll. In addition, total particulate concentrations were highest nearshore. Although the drifter slippage was approximately 1 cm/s, the biological, chemical, and physical characteristics of the water were affected by both in situ changes and vertical motions of the water. These results are generally consistent with results from other up welling studies.

On the damping of free coastal-trapped waves

Abstract: A perturbative method is presented for estimating the decay time of subinertial coastal-trapped waves under a wide range of conditions where damping is relatively weak Bottom friction is sometimes much more important than “long-wave” results would suggest, even in the parameter range where the waves are approximately non-dispersive The presence of a mean flow can greatly change the effect of bottom friction Specifically, if the mean flow over the shelf has positive (negative) relative vorticity in the Northern (Southern) Hemisphere, wave damping increases This mean flow effect appears to account for the failure of coastal-trapped waves to propagate into the Agulhas between Port Elizabeth and Durban, South Africa