East Pacific ocean eddies and their relationship to subseasonal variability in Central American wind jets

Subseasonal variability in sea surface height (SSH) over the East Pacific warm pool off Central America is investigated using satellite observations and an eddy-resolving ocean general circulation model. SSH variability is organized into two southwest-tilted bands on the northwest flank of the Tehuantepec and Papagayo wind jets and collocated with the thermocline troughs. Eddy-like features of wavelength ∼600 km propagate southwestward along the high-variance bands at a speed of 9-13 cm/s. Wind fluctuations are important for eddy formation in the Gulf of Tehuantepec, with a recurring interval of 40-90 days. When forced by satellite wind observations, the model reproduces the two high-variance bands and the phase propagation of the Tehuantepec eddies. Our observational analysis and model simulation suggest the following evolution of the Tehuantepec eddies. On the subseasonal timescale, in response to the gap wind intensification, a coastal anticyclonic eddy forms on the northwest flank of the wind jet and strengthens as it propagates offshore in the following two to three weeks. An energetics analysis based on the model simulation indicates that besides wind work, barotropic and baroclinic instabilities of the mean flow are important for the eddy growth. Both observational and model results suggest a re-intensification of the anticyclonic eddy in response to the subsequent wind jet event. Off Papagayo, ocean eddy formation is not well correlated with local wind jet variability. In both the Gulfs of Tehuantepec and Papagayo, subseasonal SSH variability is preferentially excited on the northwest flank of the wind jet. Factors for this asymmetry about the wind jet axis as well as the origins of wind jet variability are discussed.