Interciencia ISSN: 0378-1844 [email protected] Asociación Interciencia Venezuela

Aguirre Gómez, Raúl; Salmerón García, Olivia; Álvarez, Román Satellite observations of the effect of enso on the Tehuantepec and Papagayo upwellings Interciencia, vol. 37, núm. 11, noviembre, 2012, pp. 828-832 Asociación Interciencia Caracas, Venezuela

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How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative SATELLITE OBSERVATIONS OF THE EFFECT OF ENSO ON THE TEHUANTEPEC AND PAPAGAYO UPWELLINGS

Raúl Aguirre-Gómez, Olivia Salmerón-García and Román Álvarez

SUMMARY

The effects of El Niño Southern Oscillation 1997-1998 on the veal an increment of 3 and 4ºC during the El Niño year 1997- Eastern Tropical Pacific Ocean are evaluated for the Tehuan- 1998 compared with previous and subsequent years, and the tepec () and Papagayo (Costa Rica) upwelling regions. inhibition of upwelling events. It was also observed that dur- The influence of this phenomenon was observed by comparing ing ‘La Niña’, winter 1998-1999, conditions for upwelling events sea surface temperature anomalies over a 3-year period, from were re-established. winter 1996-1997 to winter 1999-2000. Satellite observations re-

he continental region un‑ Thus, masses of cold air (Hurd, 1929; der study corresponds to originating in north-western Canada move Stumpf, 1975). the Eastern Tropical Pa‑ south and east across the North American Then, according to the cific Ocean (ETPO) and includes the Great Plains and penetrate into the tropics conventional approach, the cold front contin‑ coasts of State, southern Mexico, through the during the au‑ ues to move south-eastward, creating rela‑ and the Honduran, Nicaraguan and Costa tumn, winter, and early spring. The south‑ tively high surface pressure with a lag of a Rican coasts in Central America. The re‑ ward movement of polar air creates a day or two in the south-western Caribbean gion (Figure 1) is characterized by three strong pressure gradient along the gap Sea. Hence, the pressure difference between low-elevation gaps in the Sierra Madre axes. Firstly, high-pressure systems, pres‑ the Caribbean and the Pacific triggers a Mountains of southern Mexico (Chivela ent behind each cold front, create a large wind jet that blows through the Nicaraguan Pass) and Central America (Rivas Chan‑ pressure difference at sea level across the Lake District. This results in strong easterly nel), including the mountain gap at the Isthmus of Tehuantepec, and this generates surface winds that extend far into the ETPO, Gulf of Panama, not considered in this northerly winds through the Chivela Pass west of the Gulf of Papagayo. Winds in the work. The gaps strongly affect local condi‑ and, consequently, a strong wind jet over study area are locally known as tehuanos at tions by channeling winds along their axes, the Gulf of Tehuantepec. Wind jets induce the Isthmus of Tehuantepec and papagayos thereby creating exceptional meteorological strong surface water transport westwards at the Nicaraguan Lake District. High sur‑ conditions that result in intense wind jets as a major plume, generating upwelling face pressure over the south-western Carib‑ that blow offshore over the ETPO at irreg‑ and mixing the water column. These bean Sea also generates northerly surface ular intervals of time. The characteristics winds are generated by the difference in winds across the Isthmus of Panama and of the analyzed area have been widely de‑ atmospheric pressure, this being higher over the Gulf of Panama in the ETPO. How‑ scribed elsewhere (Love, 1975; Stumpf and over the Gulf of Mexico and the western ever, Chelton et al. (2000) have found that Legeckis, 1977; McCreary et al., 1989). Caribbean Sea and low over the eastern high-pressure systems in the Caribbean Sea Hence, we will mention only those aspects Pacific Ocean. The pressure gradients are not the only mechanism for the creation relevant to this study. drive strong winds through gaps in the of jets in the Papagayo area. They found that

KEYWORDS / Eastern Tropical Pacific Ocean / ENSO / SST Anomalies / Upwelling Regions / Received 11/08/2010. Modified: 11/15/2012. Accepted: 11/28/2012.

Raúl Aguirre Gómez. Ph.D. in Physical Oceanography, University of Southampton, UK. Re‑ searcher, Universidad Nacional Autónoma de México (UNAM). Address: Instituto de Geografía, UNAM. Circuito Exterior, Ciudad Universitaria, DF, 04510, Mexico. e-mail: [email protected] Olivia Salmerón García. Doctor in Geography, UNAM, Mexico. Research Assistant, Instituto de Geografía, UNAM, Mexico. Román Álvarez. Ph.D. in Geosciences, University of California at Berkeley, USA, Researcher, Instituto de Investigaciones en Matemáticas Aplicadas y Sistemas, (UNAM), Mexico.

828 0378-1844/12/11/828-05 $ 3.00/0 NOV 2012, VOL. 37 Nº 11 Caribbean trade winds could also trigger offshore winds in the Gulfs of Papagayo and Panama, since these winds may or may not be statistically related to high- pressure systems. Average wind speed for tehuanos measured at Salina Cruz, Mexico, is 10m·s‑1; however, they may often exceed 30m·s‑1 (Hill, 1969; Stumpf, 1975; Barton et al, 1993). Tehuanos and papagayos blow over ETPO waters characterized by a shal‑ low mixed layer above a sharp thermocline. Consequently, mixing of the upper ocean by the overlying wind can cause a dramatic decrease in sea surface temperature (SST), which can be measured by radiometers on satellites. The Gulf of Tehuantepec is situated off the Pacific coast of southern Mexico, and centred at 16ºN and 95ºW. In‑ frared imagery (AVHRR) has been used for studying this area (Stumpf, 1975; Clarke, 1988; Legeckis, 1988; McCreary et al., 1989; Lavín et al., 1992; Trasviña et al., 1995), and major events during winter and spring have been observed as large negative temperature anomalies, extending hundreds of kilometres seaward. This thermal anom‑ Figure 1. Topographic characteristics of the study area (box) and selected transects at the Gulf aly has been attributed to mixing and up‑ of Tehuantepec (solid line) and the Gulf of Papagayo (dotted line). welling induced by the curl of wind stress (Roden, 1961). The upwelling describes a typical comma-shaped area, whose western on the distribution of nutrients, phytoplank‑ which migrates northward in ENSO events, edge extends from the head of the gulf ton and zooplankton off the Pacific coast of covering practically the totality of the ETPO. southward, roughly along 95ºW following Central America. the wind axis. The apparent thermal con‑ However, every 3-5 Table I trast between some of these features and years these conditions dra‑ Classification of wind strength the waters surrounding them has allowed matically change, (ENSO across the Gulf of Tehuantepec and the study of the mesoscale coastal circula‑ phenomena), the pressure the Gulf of Papagayo tion of the Gulf of Tehuantepec with the being higher than normal Comments support of infrared sensors such as in the south-western Pacific Year-month Classification on year AVHRR (Trasviña et al., 1995; González- region (low precipitation) 94-11 M- Silveira et al., 2004). and lower in the south- 94-12 M+ ? The Gulf of Papagayo is eastern Pacific (Southern 95-01 M+ centred at around 11ºN and 85ºW. Winds Oscillation). In these years 95-02 M+ appear to vary considerably in this region, the SST in the central and being stronger at Rivas than at Managua. eastern part of the ETPO 95-11 M- Rivas is under the influence of winds blow‑ area becomes anomalously 95-12 L ? ing westwar