Journal of the Marine Biological Association of India

Volume 43 Issue 1&2

On the physical aspects of Henry Stommel's theory of intensification of western boundary currents and Ekman spiral of currents.

A. V. S. Murty

Henry Stommel arrived at vorticity equation of subtropical gyre of the wind-driven oceanic currents, by taking into consideration of the frictional force and coriolis force and also by following the general convention of direction of frictional force. He was the first scientist to discover the importance of planetary vorticity to intensify the western boundary currents of the gyre. His 2- dimensional, horizontal, theory in this regard is described in simple physical terms in this paper.

Considering the same two forces, Walfrid Ekman framed in his own way I-dimentional vertical variation of winddriven horizontal currents veering to the right in N.H. and decreasing exponentially with depth. The system of currents is known as Ekman spiral. The depth above which only significant currents occur is called by Ekman the depth of frictional resistance. The surface current of the spiral makes 45" to the right of wind flow.

Stommel's model of intensification of western boundary currents and Ekman's model of vertically spiral horizontal currents are dealt with here to bring out their merits and limitations, if any, from the physical point of view with the aim of stimulating the young oceanographers. As the vertically integrated horizontal transport of water from the Ekman spiral makes 90" to the wind, near shore upwelling, where the wind blows along the coast with the land mass to the left of wind, is conveniently attributed to the transport from the spiral. As the transport has its origin in one dimensional vertical spiral of currents, it would not have a measurable or estimable direct effect on upwelling which is practically 3dementional covering over wider area.



Date : 30-12-2001