Characteristics of wind-generated rings in the eastern tropical Pacific Ocean

Eddies are generated in the eastern tropical Pacific (3 degrees S-23 degrees N, 75 degrees-105 degrees W) by winds blowing through Central American mountain passes from the Atlantic. We used Coastal Zone Color Scanner (CZCS) and advanced very high resolution radiometer (AVHRR) satellite imagery complemented with monthly in situ sea surface temperature and wind series from the Comprehensive Ocean-Atmosphere Data Set (COADS) to study these eddies and their effect on pigment concentrations in the region. Pigment values in the Gulf of Tehuantepec generally reach higher values in November-March before those in the Gulf of Papagayo. The eddies generated in the Gulf of Tehuantepec are associated with passages of cold fronts across the Gulf of Mexico from the north, while the eddies off Papagayo and Panama are associated with increases in trade wind intensity. CZCS images showed larger numbers of eddies per season than have been previously reported on the basis of in situ and AVHRR observations or numerical simulations. We counted 13 eddies in 1979-1980, 8 in 1984-1985, and 6 in 1985-1986, The eddies transfer both energy and biological constituents from the continental margin to the offshore tropical Pacific. The eddies frequently moved distances in excess of 1500 km from their point of origin. Both anticyclonic and cyclonic eddies are generated, but in general, there are more anticyclones. Anticyclonic eddies generally moved to the southwest. Some cyclonic eddies moved to the south and southeast along the Central American coast and appeared to be trapped by the cyclonic Costa Rica thermal dome. Eddies traveled at speeds varying between 9 and 21 cm s(-1) and had diameters of 100-500 km. Phytoplankton concentrations associated with the eddies varied from similar to 2 to >10 mg m(-3) within similar to 70 km of the coast to similar to 1 mg m(-3) up to 600 km of the coast. Between late April and October, fewer eddies were observed, and phytoplankton concentrations were lower (<0.25 mg m(-3)) and more uniform over the region.