Response of the Eastern Tropical Pacific to Meridional Migration of the ITCZ: The Generation of the Costa Rica Dome

Abstract

A regional ocean circulation model with fine horizontal resolution has been developed in order to obtain a coherent seasonal picture of the eastern tropical Pacific off Central America. The Costa Rica Dome with a cyclonic circulation grows rapidly in late spring off the Gulf of Papagayo and matures in summer and early fall in accord with the northward migration of the ITCZ. In winter strong northers converging in the southernmost ITCZ from three passes in Central America excite warm anticyclonic nonlinear eddies confined in the upper layer. Those anticyclones are identified as the intermediate geostrophic eddies by Matsuura and Yamagata. The Costa Rica Dome is eroded in winter and early spring by the westward propagating warm anticyclones but, at the same time, a new embryo of the dome begins to evolve from the westward propagating cold cyclonic eddy excited off the Gulf of Papagayo by the northers. The Costa Rica Dome can be maintained by the winds with the cyclonic wind stress curl in summer only when the embryo of a cyclonic eddy is preconditioned in winter and early spring. In this respect the Costa Rica Dome may be classified into a nonlinear planetary mode, rather than a response to the local wind stress curl.