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Characteristics of Wind-Generated Rings in the Eastern Tropical Pacific Ocean

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Characteristics of Wind-Generated Rings in the Eastern Tropical Pacific Ocean View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Scholar Commons | University of South Florida Research University of South Florida Scholar Commons Marine Science Faculty Publications College of Marine Science 1-15-2000 Characteristics of Wind-Generated Rings in the Eastern Tropical Pacific Ocean Frank E. Muller-Karger University of South Florida, [email protected] Cesar Fuentes-Yaco University of South Florida Follow this and additional works at: https://scholarcommons.usf.edu/msc_facpub Part of the Marine Biology Commons Scholar Commons Citation Muller-Karger, Frank E. and Fuentes-Yaco, Cesar, "Characteristics of Wind-Generated Rings in the Eastern Tropical Pacific Ocean" (2000). Marine Science Faculty Publications. 53. https://scholarcommons.usf.edu/msc_facpub/53 This Article is brought to you for free and open access by the College of Marine Science at Scholar Commons. It has been accepted for inclusion in Marine Science Faculty Publications by an authorized administrator of Scholar Commons. For more information, please contact [email protected]. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 105, NO. C1, PAGES 1271-1284, JANUARY 15, 2000 Characteristics of wind-generated rings in the eastern tropical Pacific Ocean Frank E. Mfiller-Karger and C•sar Fuentes-Yaco Department of Marine Science,University of South Florida, St. Petersburg Abstract. Eddies are generatedin the easterntropical Pacific(3øS-23øN, 75ø-105øW) by winds blowing through Central American mountain passesfrom the Atlantic. We used CoastalZone Color Scanner(CZCS) and advancedvery high resolutionradiometer (AVHRR) satelliteimagery complemented with monthlyin situ sea surfacetemperature and wind seriesfrom the ComprehensiveOcean-Atmosphere Data Set (COADS) to study these eddies and their effect on pigment concentrationsin the region. Pigment valuesin the Gulf of Tehuantepecgenerally reach higher valuesin November-March before those in the Gulf of Papagayo.The eddiesgenerated in the Gulf of Tehuantepecare associated with passagesof cold fronts acrossthe Gulf of Mexico from the north, while the eddiesoff Papagayoand Panamfiare associatedwith increasesin trade wind intensity.CZCS images showedlarger numbersof eddiesper seasonthan have been previouslyreported 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 eddiestransfer both energy and biologicalconstituents from the continentalmargin to the offshore tropical Pacific.The eddiesfrequently moved distancesin excessof 1500 km from their point of origin. Both anticyclonicand cycloniceddies are generated,but in general,there are more anticyclones.Anticyclonic eddies generally moved to the southwest.Some cycloniceddies movedto the south and southeastalong the Central American coastand appearedto be trapped by the cyclonicCosta Rica thermal dome. Eddies traveled at speedsvarying between9 and21 cms -• andhad diameters of 100-500km. Phytoplankton concentrationsassociated with the eddiesvaried from -2 to >10 mgm -3 within-70 km of the coastto -1 mgm -3 up to 600km of thecoast. Between late April andOctober, fewereddies were observed, and phytoplankton concentrations were lower (<0.25 mg m -3) and more uniform over the region. Abajo se escapael mar al., 1999a,b]. Three mountainpasses lead to very distincteddy en la misma luz que se entrega, generationregions in the Pacificoff Central America, namely, y aunque se escapa,no sale de las manos de la tierra. the Gulf of Tehuantepec,the Gulf of Papagayo,and the Gulf of Panamfi.Eddies generatedin these regionsare referred to Underneath the sea escapes as Tehuano,Papagayo, and Panamefio,respectively. The east- in the samelight it gives, and even though it escapes,it does not leave ern tropical PacificOcean alsofeatures a large cyclonicstruc- the hands of the land. ture calledthe CostaRica thermaldome (CRTD), whichhas a Alfonso Reyes, Poet diameter ranging between 100 and 900 km and is typically (Mexico, 1889-1959) locatednear 8-11øN, 87-90øW [Cromwell,1958]. The eddiesare characterizedby low temperaturesrelative to 1. Introduction surroundingwaters and also by high concentrationsof phyto- plankton, which cause marked changesin the color of the The easterntropical PacificOcean, between 75 ø and 160øW water. The high concentrationin pigmentsresults at first from and within the Tropic of Cancer, features numerouscyclonic coastalupwelling associated with the wind jets, and the blooms and anticycloniceddies [Stumpf, 1975; Stumpf and Legeckis, are advectedoffshore in large filaments created by the wind 1977;Hoffman et al., 1981;McCreary et al., 1989;Barton et al., jets. The blooms are later promoted or maintained by up- 1993;Fiedler et al., 1991]. These eddiesare generatedas sea- welling within the eddy structure.Because of the temperature sonal winds in the Gulf of M•xico, and the trade winds from and color signalsof the eddies, satellite imagery servesas an the Caribbean are funneled through narrow mountain passes effective tool to visualize and quantify eddy motions in this in the CentralAmerican mountain range (Figure 1), producing area [cf. Stumpf, 1975; Clarke, 1988;Legeckis, 1988; Umatani strongwind jets that blow over the coastalwaters of the Pacific and Yamagata,1991; Lluch-Cota et al., 1997]. In this studywe Ocean [Matsuuraand Yamagata,1982; Clarke, 1988;Alvafez et provide new insight on the dynamicphytoplankton pigment al., 1989;McCreary et al., 1989;Hansen and Maul, 1991;Fiedler et al., 1991; Lavin et al., 1992; Trasvi•a et al., 1995; Chelton et distributionpatterns associated with the eddiesof this region and present new information in an effort to understandthe Copyright2000 by the American GeophysicalUnion. mechanismswhereby carbon and other materials are trans- Paper number 1999JC900257. ported from the marginsto the interior of the easterntropical 0148-0227/00/1999 JC900257509.00 Pacific Ocean. 1271 1272 MOLLER-KARGER AND FUENTES-YACO: EASTERN TROPICAL PACIFIC RINGS -110 -105 -100 -95 -90 -85 -80 -75 -70 ..... ß:.:'-' '"'": ii;.:'½•. ' .. ß•:. ..... ..::..•.-(::::..' ... .. • Jet "-' •- Tehuano ' O0 JetPapagayo •'•"Z•.•_•• •l' JetPanamefio :•!::: •• 'L_ -110 -105 -100 -95 -90 -85 -80 -75 -70 Figure 1. Major topographicfeatures of Mesoamericaand adjacentareas based on the ETOP05 database (National GeophysicalData Center (NGDC)). Lowlands(solid), midlands(light shading),and highlands (dark shading)of the studyarea are shown.Arrows indicate the name,location, and directionof the windjets. Wind intensityplots shownin Figure 3 were derivedfrom the row of 2ø x 2ø boxesshown centered on liøN. We showthat the spatialscales of the eddiesare similar to farther west in the CZCS data. We complementedthese data those of eddiesproduced by the Gulf Stream and Kuroshio with monthly SST and wind series from the Comprehensive currents(---250 km) and that they are typicallygenerated over Ocean-AtmosphereData Set (COADS, 1946-1987). 3-10 days [seeBarton et al., 1993]. We also describeanticy- We named eddiesin the image serieswith a numericalprefix clonic eddiesthat propagateover long distances(100-1,000 identifyingthe year of occurrence.We constructededdy names km) and that last for periodsof up to severalmonths. It was by choosingthe first letter in alphabeticalorder and addinga more difficult to discern coherent cycloniceddies because suffix identifyingthe sequentialeddy number. Finally, a letter thesedissipate within one to severalweeks [see McCreary et al., identifies the region of origin of the eddy (i.e., T, Y, or P, 1989]. The frequencyof eddy generationis highestwhen the dependingon whether the eddy was Tehuano, Papagayo,or wind jets are strongest,which is usuallyin boreal winter and Panamefio,respectively), and a sign denotesthe directionof springevery year, but the Tehuanoeddies are generatedinde- rotation (i.e., plus signfor cyclonicand minussign for anticy- pendentlyfrom thosein the more southerlypasses of Papagayo clonic). and Panamfi. We showthat much larger numbersof eddiesform in the 2.1. Ocean Color Imagery easterntropical Pacificthan has been previouslyreported on The CZCS [Hoviset al., 1980] was an experimentalsensor the basisof in situ observationsor than is predictedby numer- operated betweenOctober 1978 and June 1986 by NASA on ical modelsthat do not includerealistic, high-frequency wind the Nimbus7 satellite.Only imagesthat coveredat least some forcing.This studycontributes to documentingbetter the sta- portion of the eastern tropical Pacific and that contained tisticsand characteristicsof anticyclonicversus cyclonic eddies cloud-freeareas >---200 x 200 km2 wereselected. Figure 2 in this region.Finally, we suggestthat the wind-inducededdies summarizesthe temporal coverageachieved over the lifespan in the easterntropical Pacific Ocean transportmass, energy, of the CZCS over the area of interest. Data were screened with nutrients,plants, and animalsfrom the ocean margin to the a quick-look facility developed at NASA's Goddard Space ocean interior over distancesexceeding 1000 km. Flight Center (Greenbelt, Maryland; softwareby G. Feldman and N. Kuring). There are no major riversdischarging water into our area of 2. Methods study, and therefore the patterns observedin CZCS imagery We examinedthe shape and speedof ringswith multiyear representvariations in colordue to phytoplanktongrowth time seriesof satellite images.Specifically, we use imagery stimulatedby nutrients suppliedvia upwelling and vertical derived from NASA's Coastal Zone
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