Determining the cross-shelf scales of coastal downwelling

Idealized primitive equation numerical model experiments are used to investigate the coastal downwelling driven by an alongshore wind stress of limited alongshore extent.

Within the forced region, results are qualitatively as expected from previous two-dimensional studies: a nearshore pool of light, homogeneous water is formed, and there is a distinct front separating this pool from ambient stratified waters farther offshore. The front, given sufficient time, extends alongshore from the forcing region hundreds of kilometers “downwave” (in the sense of long coastal trapped wave propagation). Expressions are developed to predict the offshore location of the downwelling front as a function alongshore distance. The key to these scalings is to assume that the total (integrated alongshore) volume of water downwelled per unit time is balanced by a strictly alongshore flow in the “downwave” direction.