<title>Gyres observed with altimetry in the tropical Pacific Ocean</title>

Abstract

Two years of merged TOPEX-POSEIDON and ERS 1-2 altimeter data were used to investigate the evolution of gyres in the Gulf of Tehuantepec. Strong wind pulses named 'nortes' with typical structure of a jet with a fan-shaped and symmetric structure, extended from the coast to open-sea up to 200km, with its axis oriented mainly to N degree-S degree. They can reach maximum speeds of approximately 25 m/s. These 'nortes' generates a dipole-like structure in the Gulf of Tehuantepec, similar as the classical Ekman problem. The anticyclone gyre showed rotational periods of about 12 days and the cyclone 18 days. Only the anticyclone gyre can survive for more than 10 months. Annually average of more than 7 gyres are generated, mainly on winter an spring seasons. However, Sea Level Anomaly maps captured up to 25 gyres formed in the Gulfs of Tehuantepec and Papagayo. Center-gyre trajectories showed gyres traveled mainly south- westward, with translation speeds about 3-25 cm/s and diameters of 60 to 450 km. Some of these anticyclonic gyres intensify as they travel from the coast to open sea, by merging with other gyres, others decay, elongate and split or are absorbed by other gyres or the Mexican and Californian Current. The results presented in this study suggest that the generating-rate of gyres is larger than previously thought, and they can play a strong role in the exchange of properties between coast to open sea.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.