9. Las diversas facetas de El Niño y sus efectos en la costa del Perú

El fenómeno El Niño es el modo dominante de la variabilidad interanual en el Océano Pacífico, resultando de un proceso de interacción entre el océano y la atmósfera en el Pacífico Tropical, Las últimas Investigaciones demuestran que existen varias facetas de este fenómeno que varían según las modalidades de interacción entre el océano y la atmosfera así como sus ubicaciones. Existen por lo menos dos tipos de El Niño, con expresiones diferentes sobre la Temperatura Superficial del Mar en el Pacifico Tropical y en la costa de Perú: uno que se desarrolla en el Pacifico Central (tiende a estar asociado a condiciones oceánicas más frías que favorecen el estado árido de la costa peruana y condiciones oceánicas hypóxicas), y otro que se desarrolla en el Pacifico Este (que transforma la costa peruana en una “típica” zona tropical, caracterizada por aguas costeras calientes y oxigenadas, y una lluvia intensa). Hoy en día, los esfuerzos de investigación para entender los mecanismos involucrados en los diferentes tipos de El Niño han sido reforzados, dado que, en las últimas décadas, se ha incrementado la frecuencia de ocurrencia de estos eventos en el Pacifico Central, sugiriéndose que podría ser una consecuencia del cambio climático. El perfeccionamiento de los modelos regionales acoplados tanto océano - atmosfera como océano - biogeoquímlco, tiene como objetivo mejorar la comprensión de la vulnerabilidad de la biosfera peruana al cambio climático y proponer un paradigma que represente la bimodalidad de la variabilidad interanual en el Pacifico Tropical.El Niño est le mode dominant de la variabilité interannuelle dans l’océan Pacifique, résultant d’un processus d’interaction entre l’océan et l’atmosphére dans le Pacifique tropical. Les recherches récentes montrent qu’il existe plusieurs facettes de ce phénomène qui varient selon les modalités d’interaction entre l’océan et l’atmosphére et leurs emplacements. Il y a au moins deux types de El Niño, avec des expressions différentes sur la Température de surface dans le Pacifique tropical et le long de la cote du Pérou: un qui se déroule dans le Pacifique central (associé á des conditions océaniques froides qui favorisent l’état aride de la cote péruvienne et des conditions océaniques d’hypoxie), et un autre qui a lieu dans le Pacifique oriental (qui transforme la cote péruvienne en une zone tropicale «typique», caractérisé par des eaux cótiéres chaudes et oxygénées, et de fortes pluies). Aujourd’hui, les efforts de recherche pour comprendre les mécanismes impliqués dans les différents types de El Niño ont été renforcés, en raison de l’accroissement de la fréquence d’occurrence de ces événements dans le Pacifique central au cours des dernières décennies a accru, suggérant qu’ll pourrait s’agir d’une conséquence du changement dimatique. L’optimisation des modeles régionaux couplés océan - atmosphére et océan - blogéochimiques, vise à améliorer la compréhension de la vulnérabilité de la biosphére péruvienne au changement dimatique et de proposer un paradigme qui représente la bimodalité de la variabilité Interannuelle dans le Pacifique tropical.The El Niño phenomenon is the dominant mode of inter-annual variability in the Pacific Ocean, which results from the ¡nteraction between the ocean and atmosphere in the tropical Pacific. Recent research shows that there are several facets of this phenomenon, which vary according to the modalities of ¡nteraction between the ocean and atmosphere, as well as their locations. There are at least two types of El Niño with different expresslons on the sea surface temperature in the tropical Pacific and on the coast of Peru: one that takes place in the Central Pacific (which tends to be associated with colder oceanic conditions who favoring the aridity of the Peruvian coast and the ocean conditions hypoxic), and another that takes place in the Eastern Pacific (which transforms the Peruvian coast in a “typical” tropical zone, with warm and oxygenated Coastal waters, and heavy rain). Nowadays, research efforts to understand the mechanisms involved in the different types of El Niño have been strengthened, since in recent decades has increased the frequency of these events in the Central Pacific, suggesting that ¡t might be a result of climate change. The ¡mprovement of both regional models coupled ocean - atmosphere and ocean - biogeochemical aims to Improve the understanding of the vulnerability of the Peruvian biosphere to climate change, and propose a paradigm that represents the bimodality of the Inter-annual variability in the tropical Pacific

Modes of covariability between sea surface temperature and wind stress intraseasonal anomalies along the coast of Peru from satellite observations (2000-2008)

The Tropical Rainfall Measuring Mission Microwave Imager sea surface temperature (SST) and QuikSCAT wind stress satellite data are used to investigate the intraseasonal upwelling variability along the coat of Peru over the period 2000-2008. Two regions of peak variance correspond to the central Peru region (Pisco region, 15°S) and the northern Peru region (Piura region, 5°S). A covariance analysis reveals a significant coherency between winds and SST anomalies off Pisco, consistent with Ekman pumping and transport dynamics. The upwelling cell consists in a meridionally extended fringe of colder (warmer) water extending as far as 250 km from the coast at 15°S. In the Piura region, the intraseasonal covariability pattern is represented by two modes, one relevant to the direct Ekman dynamics and the other one associated with the remote forcing of intraseasonal oceanic Kelvin wave. Two regimes of variability are evidenced. A low-period regime (10-25 days) is the signature of Ekman transport/pumping dynamics and is remotely forced by the migratory atmospheric disturbances across the southeastern Pacific anticyclone. A high-period regime (35-60 day band) is associated with the combined forcing of oceanic equatorial Kelvin waves and migratory atmospheric disturbances in the midlatitudes. In particular, the modes of covariability exhibit a prominent ∼50 day period energy peak. It is shown that this period arises from the impact of the first two baroclinic modes Kelvin wave, with the second baroclinic mode Kelvin wave being more influential on the Piura region. Copyright 2011 by the American Geophysical Union.Peer Reviewe

Zooplankton volume trends off Peru between 1964 and 2001

We thank several scientists from Instituto del Mar del Perú (IMARPE) for historical record information and Sonia Sánchez and Luis O. Duarte for discussions of an earlier version of this paper. Special thanks are extended to “Gordie” Swartzman (University of Washington) for his valuable comments and help in finishing this work during his visit to IMARPE. Monthly in situ SST data were contributed by the “Dirección de Hidrografia y Navegacion (DHN)” of the Peruvian Navy. Participation in the 3rd International Zooplankton Production Symposium, 20–23 May 2003, Gijón, Spain, was made possible with financial aid from Consejo Nacional de Ciencia y Tecnologı́a del Perú (CONCYTEC) and the Eastern Pacific Consortium for Research on Global Change in Coastal and Oceanic Systems (EPCOR). Finally, we recognize the very helpful comments of the two referees.Consejo Nacional de Ciencia, Tecnología e Innovación Tecnológica - Concyte

Low-frequency modulation of intraseasonal equatorial Kelvin wave activity in the Pacific from SODA : 1958-2001

Intraseasonal equatorial Kelvin wave activity (IEKW) at a low frequency in the Pacific is investigated using the Simple Ocean Data Assimilation (SODA) oceanic reanalyses. A vertical and horizontal mode decomposition of SODA variability allows estimation of the Kelvin wave amplitude according to the most energetic baroclinic modes. A wavenumber-frequency analysis is then performed on the time series to derive indices of modulation of the IEKW at various frequency bands. The results indicate that the IEKW activity undergoes a significant modulation that projects onto baroclinic modes and is not related in a straightforward manner to the low-frequency climate variability in the Pacific. Linear model experiments corroborate that part of the modulation of the IEKW is tightly linked to change in oceanic mean state rather than to the low-frequency change of atmospheric equatorial variability

The OMZ and nutrient features as a signature of interannual and low-frequency variability in the Peruvian upwelling system

17 páginas, 3 tablas, 9 figuras.-- This work is distributed under the Creative Commons Attribution 3.0 LicenseOver the last decades, the Humboldt Current upwelling ecosystem, particularly the northern component off the coast of Peru, has drawn the interest of the scientific community because of its unique characteristics: it is the upwelling system with the biggest catch productivity despite the fact it is embedded in a shallow and intense oxygen minimum zone (OMZ). It is also an area of intense nitrogen loss and anammox activity and experiences large interannual variability associated with the equatorial remote forcing. In this context, we examined the oceanographic and biogeochemical variability associated with the OMZ off central Peru from a monthly time series (1996–2011) recorded off the coast of Callao (12° 02′ S, 77° 29′ W). The data reveal a rich spectrum of variability in the OMZ that includes frequencies ranging from seasonal to interannual scales. Due to the efficient oceanic teleconnection off Peru, the observed variability is interpreted in the light of an estimate of the equatorial Kelvin wave contribution to sea level anomalies considering the peculiarities of its vertical structure (i.e., the first two baroclinic modes). The span of the data set allows us to contrast two OMZ regimes. The "strong" regime is associated with the strong 1997–1998 equatorial Pacific El Niño, during which the OMZ adjusted to Kelvin-wave-induced downwelling conditions that switched off the upwelling and drastically reduced nutrient availability. The "weak" regime corresponds to the post-2000 period associated with the occurrence of moderate central Pacific El Niño events and enhanced equatorial Kelvin wave activity, in which mean upwelling conditions are maintained. It is shown that the characteristics of the coupling between physics and biogeochemistry is distinct between the two regimes with the weak regime being associated with a larger explained variance in biogeochemical properties not linearly related to the ENSO oceanic teleconnection. The data also reveal a long-term trend from 1999 corresponding to a deepening of the oxygen-deficient waters and warming. The implications of our results for understanding the OMZ dynamics off Peru are discussedThis research was supported by the Instituto del Mar del Peru (IMARPE). Boris Dewitte acknowledges support from FONDECYT (projects 1151185 and 1171861).Peer reviewe

An analysis of SST gradients off the Peruvian coast : the impact of going to higher resolution

The Peruvian Coastal Upwelling System (PCUS) is one of the most productive fisheries in the world. Upwelling events are associated with changes in the magnitude and location of frontal structures. SST gradients from four different data sets, NCDC, REMSS, OSTIA, and MUR are compared in two test areas off the PCUS: Paita (5 degrees S) and Pisco (14 degrees S). In both areas gradients derived from the MUR data set show greater magnitudes, as well as larger seasonal cycles. Off Pisco, the magnitude of the seasonal cycle of 2.2 degrees C/100 km in MUR is larger than the one derived from the lower resolution data sets. All data sets at Pisco exhibit a seasonal cycle that peaks in late Austral summer and early fall. Hovmoller diagrams calculated at 5.5 degrees S, 10.5 degrees S, and 14.5 degrees S show clearly defined offshore maxima in the cross-shore gradients for all the data sets. Upwelling scales determined by the distance to the first maxima vary depending on the data set used. At 5.5 degrees S upwelling scales vary from 10 km for MUR to 50 km for NCDC At 14.5 degrees S the scales vary from 20 km for MUR to 40 km for OSTIA. All four data sets show similar large-scale structures associated with the Peruvian upwelling. However, MUR shows finer scale structures that are most likely due to submesoscale to mesoscale eddies. Sub-sampled MUR 1 km data at the 25 km, 9 km, and 4 km resolutions compare well in magnitude and phase with the lower resolution products. Agreement in gradient magnitude between the lower resolution data sets and the MUR sub-sampled at their respective resolutions implies that the pixel-to-pixel analysis noise in MUR is at a similar level as the other data sets

Modes of covariability between sea surface temperature and wind stress intraseasonal anomalies along the coast of Peru from satellite observations (2000-2008)

The Tropical Rainfall Measuring Mission Microwave Imager sea surface temperature (SST) and QuikSCAT wind stress satellite data are used to investigate the intraseasonal upwelling variability along the coat of Peru over the period 2000-2008. Two regions of peak variance correspond to the central Peru region (Pisco region, 15 degrees S) and the northern Peru region (Piura region, 5 degrees S). A covariance analysis reveals a significant coherency between winds and SST anomalies off Pisco, consistent with Ekman pumping and transport dynamics. The upwelling cell consists in a meridionally extended fringe of colder (warmer) water extending as far as 250 km from the coast at 15 degrees S. In the Piura region, the intraseasonal covariability pattern is represented by two modes, one relevant to the direct Ekman dynamics and the other one associated with the remote forcing of intraseasonal oceanic Kelvin wave. Two regimes of variability are evidenced. A low-period regime (10-25 days) is the signature of Ekman transport/pumping dynamics and is remotely forced by the migratory atmospheric disturbances across the southeastern Pacific anticyclone. A high-period regime (35-60 day band) is associated with the combined forcing of oceanic equatorial Kelvin waves and migratory atmospheric disturbances in the midlatitudes. In particular, the modes of covariability exhibit a prominent similar to 50 day period energy peak. It is shown that this period arises from the impact of the first two baroclinic modes Kelvin wave, with the second baroclinic mode Kelvin wave being more influential on the Piura region