Mesoscale variability along the southwest coast of Mexico induced by oceanic and atmospheric remote forcings.

摘要

The mesoscale variability along the southwest coast of Mexico is studied using sea surface height satellite altimeter observations and the Naval Research Laboratory Layered Ocean Model. The study is divided into three parts: The formation and fate of El Niño/Southern Oscillation (ENSO) related eddies, the existence and genesis for anticyclonic eddies near Cabo Corrientes, and the life cycle of the Tehuantepec eddies.; Investigation of ENSO related eddies indicates that during strong warm ENSO events the upper ocean circulation along the southwest coast of Mexico is destabilized. The effect of ENSO appears as three distinct stages. First, a coastal jet characterized by strong vertical shear flow develops. Second, the shear flow strengthens, increasing both its horizontal dimension and the amplitude of its oscillations. Finally, the jet becomes unstable and breaks into anticyclonic eddies. The genesis and strengthening of the jet is due to the simultaneous occurrence of the poleward-flowing currents along the southwest coast of Mexico and the poleward circulation associated with warm ENSO events.; Examination of the generation of anticyclonic eddies near Cabo Corrientes indicates that the arrival of downwelling coastally trapped waves at Cabo Corrientes corresponds to intensification of local currents. The interaction of these intensified currents with the coastline geometry generates anticyclonic eddies. Comparison of different numerical simulations suggests that the bottom topography and the local wind are not responsible for the eddy generation. In contrast, the coastline geometry, most notably the cape at Cabo Corrientes, causes the formation of eddies. The existence and timing of the modeled eddies are validated with sea surface height altimeter observations and temperature hydrographic data.; Analysis of the life cycle of the anticyclonic eddies generated in the Gulf of Tehuantepec suggests that: The interannual variability of the number and strength of the Tehuantepec eddies is directly related to El Niño-La Niña cycle. These eddies migrate 5000 km, weakening (decreasing their maximum sea surface elevation) and disappearing when exposed to the cyclonic shear between the North Equatorial Current and the North Equatorial Counter Current. Outside of the equatorial region, the Tehuantepec eddies are the most energetic signal in the Eastern North Pacific Ocean.