Abstract
Equilibrium conditions in anf-plane ocean evolve as follows after the sudden onset of winds parallel to a coast. At first the flow is two-dimensional-spatial variations are confined to a plane perpendicular to the coast-and the salient features in the forcing region are acceleration of a coastal jet in the surface layers in the wind direction, and offshore Ekman drift that causes coastal upwelling. Kelvin waves excited at the edge of the forced region establish equilibrium conditions by creating an alongshore pressure gradient that balances the wind so that the acceleration stops. The vertical structure corresponding to each vertical mode differs from that of the wind-driven coastal jet so that the arrival of the barotropic Kelvin wave starts to accelerate a coastal undercurrent in a direction opposite to that of the wind. Subsequent baroclinic Kelvin waves modify the vertical structure of the coastal current so that the undercurrent in the subsurface layer is accelerated. In an inviscid model there is a singularity in the surface layers at the coast ast→∞ because the Kelvin modes with small offshore and vertical scales travel slowly and take a very long time to make their contribution to the establishment of equilibrium conditions. A modest amount of friction eliminates this problem. Nonlinearities are important in the heat equation and affect sea surface temperatures significantly but their effect on the momentum balance is secondary.
Similar content being viewed by others
References
Allen, J. S. (1976): Some aspects of the forced wave response of stratified coastal regions. J. Phys. Oceanogr.,6, 113–119.
Bryan, K. (1969): A numerical method for the study of the circulation of the world ocean. J. Comp. Phys.,4, 347–376.
Charney, J. G. (1955): The generation of ocean currents by wind. J. Mar. Res.,14, 477–498.
Crepon, M. and C.Richez (MS): Transient upwelling generated by two-dimensional atmospheric forcing and variability in the coast line. J. Phys. Oceanogr. (in press).
Gill, A. E. andA. J. Clarke (1974): Wind-induced upwelling coastal currents and sea-level. Deep-Sea Res.,21, 325–346.
Huyer, A. (1976): A comparison of upwelling events in two locations: Oregon and Northwest Africa. J. Mar. Res.,34, 531–546.
Lighthill, M. J. (1969): Dynamic response of the Indian Ocean to the onset of the southwest Monsoon. Phil. Trans. Roy. Soc. London,A265, 45–93.
McCreary, J. P. (1981): A linear stratified ocean model of the coastal undercurrent. Phil. Trans. Roy. Soc. London,A302, 385–413.
Mooers, C. N. K., C. A. Collins andR. L. Smith (1976): The dynamic structure of the frontal zone in the coastal upwelling region off Oregon. J. Phys. Oceanogr.,6, 3–21.
Peffley, M. B. andJ. J. O'Brien (1976): A three-dimensional simulation of coastal upwelling off Oregon. J. Phys. Oceanogr.,6, 164–180.
Philander, S. G. H. and J-H.Yoon (MS): Eastern boundary currents and coastal upwelling. J. Phys. Oceanogr. (in press).
Smith, R. L. (1978): Poleward propagating perturbations in currents and sea-levels along the Peru Coast. J. Geophys. Res.,83, C12, December, 6083–6092.
Suginohara, N. (1974): Onset of coastal upwelling in a two-layer ocean by wind stress with long-shore variation. J. Oceanogr. Soc. Japan,30, 23–33.
Yoshida, K. (1955): Coastal upwelling off the California coast. Rec. Oceanogr. Works Japan,15, 1–13.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Yoon, J.H., Philander, S.G.H. The generation of coastal undercurrents. Journal of the Oceanographical Society of Japan 38, 215–224 (1982). https://doi.org/10.1007/BF02111104
Received:
Revised:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF02111104