Abstract
Large-scale frontlike structures, which are not expected from a simple wind-driven ocean circulation theory, can be found in basin-scale oceanic gyres. Recent works suggest that such a structure could be caused by nonlinear stationary Rossby wavelike disturbances superimposed on the wind-driven gyres. The present article gives a brief review on this problem, after outlinig a wind-driven ocean circulation therory (Svedrup theory) and nonlinear Rossby wave dynamics.