ENSO as an integrating concept in earth science

The El Ni?o-Southern Oscillation (ENSO) cycle of alternating warm El Ni?o and cold La Ni?a events is the dominant year-to-year climate signal on Earth. ENSO originates in the tropical Pacific through interactions between the ocean and the atmosphere, but its environmental and socioeconomic impacts are felt worldwide. Spurred on by the powerful 1997-1998 El Ni?o, efforts to understand the causes and consequences of ENSO have greatly expanded in the past few years. These efforts reveal the breadth of ENSO's influence on the Earth system and the potential to exploit its predictability for societal benefit. However, many intertwined issues regarding ENSO dynamics, impacts, forecasting, and applications remain unresolved. Research to address these issues will not only lead to progress across a broad range of scientific disciplines but also provide an opportunity to educate the public and policy makers about the importance of climate variability and change in the modern world.     

Central pacific seabirds and the el nino southern oscillation: 1982 to 1983 perspectives

The breeding chronology and reproductive attempts of the seabird community on Christmas Island in the central Pacific Ocean (2 degrees N, 157 degrees W) were interrupted by the 1982-1983 El Ni?o Southern Oscillation. The resultant reproductive failure and disappearance of the entire seabird community of this equatorial atoll represents the most dramatic interruption on record of a seabird community located distant from coastal upwelling. Our data indicate the effect that the abiotic and biotic aspects of a global atmospheric-oceanic anomaly have on marine birds. The 1982-1983 El Ni?o Southern Oscillation provides an example of selective pressures and a natural experiment in the study of vertebrate population dynamics.     

Meteorological aspects of the el nino/southern oscillation

The single most prominent signal in year-to-year climate variability is the Southern Oscillation, which is associated with fluctuations in atmospheric pressure at sea level in the tropics, monsoon rainfall, and wintertime circulation over North America and other parts of the extratropics. Although meteorologists have known about the Southern Oscillation for more than a half-century, its relation to the oceanic El Ni?o phenomenon was not recognized until the late 1960's, and a theoretical understanding of these relations has begun to emerge only during the past few years. The past 18 months have been characterized by what is probably the most pronounced and certainly the best-documented El Ni?o/Southern Oscillation episode of the past century. In this review meteorological aspects of the time history of the 1982-1983 episode are described and compared with a composite based on six previous events between 1950 and 1975, and the impact of these new observations on theoretical interpretations of the event is discussed.     

Reduced interannual rainfall variability in East Africa during the last ice age

Interannual rainfall variations in equatorial East Africa are tightly linked to the El Ni?o Southern Oscillation (ENSO), with more rain and flooding during El Ni?o and droughts in La Ni?a years, both having severe impacts on human habitation and food security. Here we report evidence from an annually laminated lake sediment record from southeastern Kenya for interannual to centennial-scale changes in ENSO-related rainfall variability during the last three millennia and for reductions in both the mean rate and the variability of rainfall in East Africa during the Last Glacial period. Climate model simulations support forward extrapolation from these lake sediment data that future warming will intensify the interannual variability of East Africa's rainfall.     

Elimination of two reef-building hydrocorals following the 1982-83 el nino warming event

One probable extinction and one range reduction of eastern Pacific reef-building hydrocoral (Millepora) species mark the first documented cases of species eliminations resulting from the worldwide 1980s coral reef bleaching events. Two of 12 Panamanian coral species were eliminated suddenly from their former ranges by prolonged high sea temperatures during the 1982-83 El Ni?o-Southern Oscillation event. Three conditions contributed to their demise: high sensitivity to sea warming, populations confined to a small geographic area, and bathymetric restriction to the euphotic zone (相似文献   

Super ENSO and global climate oscillations at millennial time scales

The late Pleistocene history of seawater temperature and salinity variability in the western tropical Pacific warm pool is reconstructed from oxygen isotope (delta18O) and magnesium/calcium composition of planktonic foraminifera. Differentiating the calcite delta18O record into components of temperature and local water delta18O reveals a dominant salinity signal that varied in accord with Dansgaard/Oeschger cycles over Greenland. Salinities were higher at times of high-latitude cooling and were lower during interstadials. The pattern and magnitude of the salinity variations imply shifts in the tropical Pacific ocean/atmosphere system analogous to modern El Ni?o-Southern Oscillation (ENSO). El Ni?o conditions correlate with stadials at high latitudes, whereas La Ni?a conditions correlate with interstadials. Millennial-scale shifts in atmospheric convection away from the western tropical Pacific may explain many paleo-observations, including lower atmospheric CO2, N2O, and CH4 during stadials and patterns of extratropical ocean variability that have tropical source functions that are negatively correlated with El Ni?o.     

Impacts of a global climate cycle on population dynamics of a migratory songbird

Progress toward understanding factors that limit abundances of migratory birds, including climate change, has been difficult because these species move between diverse locations, often on different continents. For black-throated blue warblers (Dendroica caerulescens), demographic rates in both tropical winter quarters and north temperate breeding grounds varied with fluctuations in the El Ni?o Southern Oscillation. Adult survival and fecundity were lower in El Ni?o years and higher in La Ni?a years. Fecundity, in turn, was positively correlated with subsequent recruitment of new individuals into winter and breeding populations. These findings demonstrate that migratory birds can be affected by shifts in global climate patterns and emphasize the need to know how events throughout the annual cycle interact to determine population size.     

Biospheric primary production during an ENSO transition

The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) provides global monthly measurements of both oceanic phytoplankton chlorophyll biomass and light harvesting by land plants. These measurements allowed the comparison of simultaneous ocean and land net primary production (NPP) responses to a major El Ni?o to La Ni?a transition. Between September 1997 and August 2000, biospheric NPP varied by 6 petagrams of carbon per year (from 111 to 117 petagrams of carbon per year). Increases in ocean NPP were pronounced in tropical regions where El Ni?o-Southern Oscillation (ENSO) impacts on upwelling and nutrient availability were greatest. Globally, land NPP did not exhibit a clear ENSO response, although regional changes were substantial.     

Ecology. Weather ruins winter vacations

There has been increasing concern over the decline in many migratory bird species. As Saether discusses in his Perspective, evidence is accumulating (Sillett et al.) that climate change resulting from the El Ni?o Southern Oscillation affects both the survival rate of adult birds at tropical wintering sites and their reproductive rate at summer breeding grounds in the Northern Hemisphere.     

Eocene El Niño: evidence for robust tropical dynamics in the "hothouse"

Much uncertainty surrounds the interactions between the El Ni?o-Southern Oscillation (ENSO) and long-term global change. Past periods of extreme global warmth, exemplified by the Eocene (55 to 35 million years ago), provide a good testing ground for theories for this interaction. Here, we compare Eocene coupled climate model simulations with annually resolved variability records preserved in lake sediments. The simulations show Pacific deep-ocean and high-latitude surface warming of approximately 10 degrees C but little change in the tropical thermocline structure, atmosphere-ocean dynamics, and ENSO, in agreement with proxies. This result contrasts with theories linking past and future "hothouse" climates with a shift toward a permanent El Ni?o-like state.     

Oceanographic events during el nino

El Ni?o events, the most spectacular instances of interannual variability in the ocean, have profound consequences for climate and the ocean ecosystem. The 1982-1983 El Ni?o is perhaps the strongest in this century. El Ni?o events usually have followed a predictable pattern, but the recent event differs markedly. The physical oceanography of this El Ni?o is described and compared with that of earlier events.     

Deep ocean impact of a Madden-Julian oscillation observed by Argo floats

Using the new Argo array of profiling floats that gives unprecedented space-time coverage of the upper 2000 meters of the global ocean, we present definitive evidence of a deep tropical ocean component of the Madden-Julian Oscillation (MJO). The surface wind stress anomalies associated with the MJO force eastward-propagating oceanic equatorial Kelvin waves that extend downward to 1500 meters. The amplitude of the deep ocean anomalies is up to six times the amplitude of the observed annual cycle. This deep ocean sink of energy input from the wind is potentially important for understanding phenomena such as El Ni?o-Southern Oscillation and for interpreting deep ocean measurements made from ships.     

The possible link between net surface heating and el nino

Three diagnostic analyses are described which strongly suggest the importance of local net surface heating in the life history of the large-scale, air-sea phenomenon centered in the eastern tropical Pacific Ocean, commonly called El Ni?o. These analyses rely upon monthly marine weather summaries for the period 1957 to 1976. In the first, correlations and coherence spectra were calculated which show a strong link between the net surface heat flux and sea-surface temperature variations over the eastern equatorial Pacific. The second analysis, also based upon the use of coherence spectra, indicates a sea temperature precursor in the eastern ocean near 25 degrees S which precedes sea temperature changes near the El Ni?o focus near 5 degrees S. Since the link between the two regions would require ocean advective velocities that appear to be unreasonably large, this analysis also suggests the importance of atmospheric forcing through the surface heat flux. In the third analysis a proxy variable is described that seems to be a reasonable indicator of the overall effect of ocean dynamics on the temperature of the El Ni?o core region. A composite analysis of the four El Ni?o events of 1957, 1965, 1972, and 1976 suggests that local surface heating is important during the early part of an event, whereas dynamical factors dominate later.     

Recent variability in the southern oscillation: isotopic results from a tarawa atoll coral

In the western tropical Pacific, the interannual migration of the Indonesian Low convective system causes changes in rainfall that dominate the regional signature of the El Ni?o-Southern Oscillation (ENSO) system. A 96-year oxygen isotope record from a Tarawa Atoll coral (1 degrees N, 172 degrees E) reflects regional convective activity through rainfall-induced salinity changes. This monthly resolution record spans twice the length of the local climatological record and provides a history of ENSO variability comparable in quality with those derived from instrumental climate data. Comparison of this coral record with a historical chronology of EI Ni?o events indicates that climate anomalies in coastal South America are occasionally decoupled from Pacific-wide ENSO extremes. Spectral analysis suggests that the distribution of variance in this record has shifted among annual to interannual periods during the present century, concurrent with observed changes in the strength of the Southern Oscillation.     

Cholera dynamics and El Niño-Southern Oscillation

Analysis of a monthly 18-year cholera time series from Bangladesh shows that the temporal variability of cholera exhibits an interannual component at the dominant frequency of El Ni?o-Southern Oscillation (ENSO). Results from nonlinear time series analysis support a role for both ENSO and previous disease levels in the dynamics of cholera. Cholera patterns are linked to the previously described changes in the atmospheric circulation of south Asia and, consistent with these changes, to regional temperature anomalies.     

Cool La Niña during the warmth of the Pliocene?

The role of El Ni?o-Southern Oscillation (ENSO) in greenhouse warming and climate change remains controversial. During the warmth of the early-mid Pliocene, we find evidence for enhanced thermocline tilt and cold upwelling in the equatorial Pacific, consistent with the prevalence of a La Ni?a-like state, rather than the proposed persistent warm El Ni?o-like conditions. Our Pliocene paleothermometer supports the idea of a dynamic "ocean thermostat" in which heating of the tropical Pacific leads to a cooling of the east equatorial Pacific and a La Ni?a-like state, analogous to observations of a transient increasing east-west sea surface temperature gradient in the 20th-century tropical Pacific.     

Breeding patterns of galapagos penguins as an indicator of oceanographic conditions

Surface water changes associated with El Ni?o have been known to affect deleteriously top carnivores along coastal South America. Data on the breeding strategies of Galápagos penguins and other seabirds indicate that the biological effects of El Ni?o extend much farther west. The breeding biology of these seabirds is adapted to frequent changes in productivity which are associated with El Ni?o.     

The el nino cycle: a natural oscillator of the pacific ocean--atmosphere system

Research conducted during the past decade has led to an understanding of many of the mechanisms responsible for the oceanic and atmospheric variability associated with the El Ni?o-Southern Oscillation (ENSO). However, the reason for one of the fundamental characteristics of this phenomena, its quasi-periodicity, has remained unclear. Recently available evidence from a number of sources now suggests that the ENSO "cycle" operates as a natural oscillator based on relatively simple couplings between the tropical atmospheric circulation, the dynamics of the warm upper layer of the tropical ocean, and sea surface temperatures in the eastern equatorial Pacific. This concept and recent field evidence supporting the natural coupled oscillator hypothesis are outlined.     

El nino: a chaotic dynamical system?

Most of the principal qualitative features of the El Ni?o-Southern Oscillation phenomenon can be explained by a simple but physically motivated theory. These features are the occurrence of sea-surface warmings in the eastern equatorial Pacific and the associated trade wind reversal; the aperiodicity of these events; the preferred onset time with respect to the seasonal cycle; and the much weaker events in the Atlantic and Indian oceans. The theory, in its simplest form, is a conceptual model for the interaction of just three variables, namely near-surface temperatures in the east and west equatorial ocean and a wind-driven current advecting the temperature field. For a large range of parameters, the model is naturally chaotic and aperiodically produces El Ni?o-like events. For a smaller basin, representing a smaller ocean, the events are proportionally less intense.     

On the prediction of the el nino of 1986-1987

Three different classes of numerical models successfully predicted the occurrence of the El Ni?o of 1986-87 at lead times of 3 to 9 months. Although the magnitude and timing of predicted ocean surface temperatures were not perfect, these results suggest that routine prediction of moderate to lare El Ni?o events is feasible. The key to the success of the models lies in recognizing or simulating the low-frequency, large-scale changes in the tropical ocean-atmosphere system that give rise to El Ni?o events.