Inertial wind path and sea surface temperature patterns near the Gulf of Tehuantepec and Gulf of Papagayo

Abstract

During the northern hemisphere winter the surface atmospheric pressure on the Gulf of Mexico side of Central America is often higher than that on the Pacific side. The resultant southward pressure gradient drives strong southward winds through a gap in the Sierra Madre mountain range at the Isthmus of Tehuantepec. The atmospheric jet is narrow in comparison with the relevant radius of deformation, so when it leaves the coast and flows out over the Gulf of Tehuantepec, it is an inertial jet. Therefore the jet is expected to be deflected into a clockwise inertial circle by the Coriolis force. A similar process should also occur for Central American atmospheric jets through mountain range gaps near the Gulf of Papagayo. Satellite measurements of sea surface temperature together with coastal wind data for the first 41 days of 1986 were examined to see if the expected wind path influenced sea surface temperature (SST) near the Gulf of Tehuantepec and the Gulf of Papagayo. Consecutive daily satellite images when the coastal southward Tehuantepec wind increased suggest that the initial development of cold surface water in a clockwise loop is due to the wind mixing the shallow thermocline surface water along its inertial path. A simple 1½‐layer analytical ocean model suggests, in agreement with observations, that the wind can drive surface quasi‐geostrophic currents of ∼1 m s−1. Since the wind path is circular, the wind actually generates a clockwise rotating ocean eddy with the approximate scale of the wind inertial circle. The satellite sea surface temperature measurements also suggest that the wind‐driven surface ocean current is unstable. In addition, stronger gradients in SST to the right of the expected wind flow are consistent with advection of sea surface temperature by ocean surface Ekman flow.