An Ekman Model of Coastal Currents in a Lake or Shallow Sea

Abstract

Coastal currents are investigated by use of asymptotic solutions in a steady-state barotropic lake or shallow sea of variable depth, with only vertical eddy viscosity and zero Rossby number. Earlier work has been extended to permit the depth to vanish at the coast. Two coastal horizontal scales are distinguished. An E¼ scale, where E is the Ekman number, is responsible for horizontal mass balance, carrying mass around the coast from regions of surplus to regions of deficit. An E½ scale motion is primarily responsible for upwelling and reducing the flow to rest at the coast. The solution is calculated explicitly for a circular parabolic basin; an approximate local solution for a coastal current on the north shore of Lake Ontario is found and compared with observations. Qualitative agreement is found, but the predicted coastal current is somewhat broader than that observed.