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

Eddies are generated in the eastern tropical Pacific (3 degrees S-23 degree s N, 75 degrees-105 degrees W) by winds blowing through Central American mo untain passes from the Atlantic. We used Coastal Zone Color Scanner (CZCS) and advanced very high resolution radiometer (AVHRR) satellite imagery comp lemented with monthly in situ sea surface temperature and wind series from the Comprehensive Ocean-Atmosphere Data Set (COADS) to study these eddies a nd their effect on pigment concentrations in the region. Pigment values in the Gulf of Tehuantepec generally reach higher values in November-March bef ore those in the Gulf of Papagayo. The eddies generated in the Gulf of Tehu antepec are associated with passages of cold fronts across the Gulf of Mexi co from the north, while the eddies off Papagayo and Panama are associated with increases in trade wind intensity. CZCS images showed larger numbers o f eddies per season than have been previously reported on the basis of in s itu and AVHRR observations or numerical simulations. We counted 13 eddies i n 1979-1980, 8 in 1984-1985, and 6 in 1985-1986, The eddies transfer both e nergy and biological constituents from the continental margin to the offsho re tropical Pacific. The eddies frequently moved distances in excess of 150 0 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 b y the cyclonic Costa Rica thermal dome. Eddies traveled at speeds varying b etween 9 and 21 cm s(-1) and had diameters of 100-500 km. Phytoplankton con centrations 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 60 0 km of the coast. Between late April and October, fewer eddies were observ ed, and phytoplankton concentrations were lower (<0.25 mg m(-3)) and more u niform over the region.