Southern Oscillation

Direct physical effects and cascading trophic interactions operate together to determine interannual variability in the seasonal pattern .of primary productivity at Castle Lake, California. Principal component analysis was used to investigate the depth-time distributions of productivity for summers 196 l-l 986. Two characteristic patterns were found, together accounting for 60-70% of the year-to-year variability. The first pattern corresponds to the deep productivity maximum that forms in the hypolimnion in June and July. Variability in this first pattern arises from the direct effects on phytoplankton populations of year-to-year changes in timing of ice breakup and hydraulic flushing in spring. The first pattern is unusually strong or weak, compared to the longterm average, during the phenomenon of El Niiio-Southern Oscillation. A second characteristic pattern corresponds to the mixed-layer productivity maximum that develops in August and September. Variability in this second pattern arises from trophic interactions at higher levels: rainbow trout feed on late-summer Daphnia rosea populations, which in turn graze on the mixed-layer algal community. In addition, some of the variability in the rainbow trout population arises from yearto-year differences in angling pressure from humans. These results demonstrate how interannual variability in an ecosystem property (primary productivity) can be controlled by forces acting simultaneously through the top and the base of the food web.

The White-tailed Tropicbird Phaethon lepturus breeding population of Aride Island, Seychelles, has experienced a strong decline in the recent past. To predict the future trends of the White-tailed Tropicbird population on Aride Island and understand the urgency of applying management procedures, we developed a population matrix model. We estimated White-tailed Tropicbird adult survival rate over a 12-year period and investigated whether oceanographic conditions (El Niño Southern Oscillation, ENSO, and inter-annual climate variability in the Indian Ocean, Indian Ocean Dipole, IOD) or local factors (Pisonia grandis fruiting events) potentially affect adult survival. Annual adult survival could not be linked to inter-annual variability in oceanographic conditions, but may be more influenced by Pisonia fruiting events, which, overall, accounts for 23.2% of the adult mortality. The growth rate of the population, primarily influenced by annual adult survival, was estimated to be 0.946, which indicates an annual population decline of 5.4%. At the current rate, the probability of extinction of this population would be 99% in 170 years. Management scenarios studied through Monte Carlo simulations, assuming small increments in adult survival and/or breeding success, dramatically reduce the risk of extinction of White-tailed Tropicbirds. Habitat management, in order to maintain an open canopy and little understorey vegetation, appears to be crucial for the conservation of White-tailed Tropicbirds on Aride Island, as has already been shown for other groundnesting tropical seabirds nesting on forested islands.

Unravelling the epidemiology of cholera has been one of the most elusive problems in tropical medicine. The early contest between 'contagionists' and 'localists' in the last century finds a modern equivalent in the on-going debate on whether the epidemiology of cholera has significant environmental determinants. This study investigates the role of climate and geography on seasonality and interannual variations of cholera, using historical mortality data between 1891 and 1940 from 24 districts of Bengal. The coastal districts exhibit a bi-annual seasonal cycle, as previously described for cholera in this region, but with a dominant peak in the spring. Spring mortality, particularly in the coastal region, shows significant correlations (r = 0.50, p < 0.001) with sea surface temperatures in the Bay of Bengal. During post-Niño years (a total of 13 events) when coastal sea temperatures rise, spring epidemics with excess mortality (over 15 000 deaths on average) occur, resulting in a shift away from the usual seasonal pattern. Significant correlations (r = 0.58, p < 0.001) between sea temperatures in the Pacific (an El Niño index) and cholera's spring deaths, and a peak at a frequency of approximately 1 /4.2 years in the power spectrum, support the influence of this climatic forcing. Cholera's winter peak, dominant further away from the estuary, appears less consistently associated with water temperatures in the Bay of Bengal, and accounts for most of the interannual variation in the geographical spread of cholera in Bengal. The differences in our results for spring and winter suggest the possibility of different aquatic reservoirs for the pathogen. As sea water temperature can only explain part of the historical variability in cholera deaths, and the seasonality of temperature is similar to that of other environmental parameters, further studies to elucidate causal pathways are warranted. Here, we provide geographical and climatological support for the hypothesis that environmental factors are important in the dynamics of endemic cholera.

The western boundary of the tropical Pacific is not continuous, and leakage of low-frequency energy from the Pacific to the Indian Ocean is possible. At low frequencies, equatorial Kelvin and Rossby waves have very large east-west scales compared with the east-west scale of the land masses in the region. Consequently, these land masses may be treated as islands that are infinitesimally thin in the east-west direction. By generalizing previous theory for a single island, the leakage and multiple reflection of low-frequency energy through the seven major "islands" forming the boundary of the western Pacific can be studied. The results obtained depend on continuity of mass and large-scale balances and not on the details of nonlinear and/or frictional flow near island eastern boundaries. The major results are as follows: (1) When a mode 1 low-frequency Rossby wave is reflected at the discontinuous western Pacific boundary, the eastward reflected Kelvin wave energy flux is about one third of the incoming energy flux, or about two thirds of that expected for a solid meridional wall. In other words, the reflected Kelvin wave amplitude is 83% of that which would be reflected from a solid meridional wall. The reflection mainly occurs from the Indonesia/Borneo/Asia land mass and very little energy gets into the Indian Ocean. (2) Sea levels in the western equatorial Pacific and on the western boundaries of the major western Pacific land masses should be in phase and of a similar amplitude. In particular, in-phase interannual sea levels should occur along Australia's western coast and be highly correlated with sea levels in the western equatorial Pacific. Sea level data at Truk Island and on Australia's western coastline confirm this prediction. (3) The interannual exchange of water between the Pacific and Indian oceans due to interannual oscillations in the Pacific is about 6 Sv (1 Sv-10 6 m 3 s-•), is highly correlated with El Nifio/Southern Oscillation (ENSO) events, and bears definite phase relationships to sea level stations at locations in the western Pacific. For example, for a high sea level at Darwin, the transport is westward from the Pacific Ocean into the Indian Ocean. it seems that interannual transport may be approximately monitored using coastal sea level. (4) Strong narrow low-frequency currents are predicted to occur westward of some island tips. (5) Interannual indian Ocean Kelvin wave signals are largely blocked at the Indonesia/Borneo/Asia land mass. (6) In terms of net transport, reflection, and transmission properties, the seven island Pacific western boundary can be reduced to a simpler two-island problem, in which one island is the Indonesia/Borneo/Asia land mass and the other New Guinea/Australia. (7) The comparatively small Halmahera Sea between Halmahera and New Guinea is dynamically important. Closing this sea for the incident first meridional mode Rossby wave case reduces the interannual transport between the Pacific and Indian Oceans by 40%.

Observed changes in maternal investment due to an environmentally induced decrease in food supply (the 1983 El Niño-Southern Oscillation) are compared witha priori predictions for the California sea lion (Zalophus californianus). Changes in behavior, growth and mortality of off-spring were also examined. Data collected in the first two months postpartum for the years before (PRE), during (EN), and the two years after (POST1 and POST2) the 1983 El Niño indicate that females initiated postpartum feeding trips earlier during the food shortage, and spent more time away on individual feeding trips in both the El Niño year and the year after. Perinatal sex ratios (♀:♂) in the years PRE, EN, POST1 and POST2 were 1:1, 1.4:1, 1.1:1 and 1:1.4, respectively. Fewer copulations were observed during the El Niño year, but this difference was not statistically significant. Pups spent less time suckling in the food shortage year and the year following, but attempted to sneak suckle more. Pups were less active and played on land less in the El Niño and following year. Finally, maternal investment as measured by milk intake of offspring was decreased, pups grew more slowly, and suffered increased mortality during the food shortage year. Despite expected sex differences in maternal investment and pup behavior in response to food shortage, there were no sex-biased differences in response in either females or pups. As expected, the food shortage did not affect adult males since they migrate north during the non-breeding season where the environmental perturbation was less severe.

Archaeological research in the Australia's northeast Queensland rainforest and margins has revealed a human antiquity of at least 8000 cal year BP within the rainforest and at least 30,000 years on the western edge. Rainforest occupation before 2000 cal year BP was at generally very low levels, after which time settlement of this environment became intensive and probably permanent. Exploitation of toxic varieties of nuts began about 2500 cal year BP, peaking after 1500 cal year BP. This economic development appears crucial to successful human adaptation to rainforests in the area and was pivotal in facilitating the long-term permanent human settlement of the wet tropics. The role of fire, El Niño Southern Oscillation (ENSO) activity and shifting vegetation regimes were important catalysts in providing opportunities for permanent Australian rainforest Aboriginal occupation. The results have implications for global understandings of rainforest occupation by modern people. It demonstrates the wide temporal and spatial variability of human rainforest colonization processes worldwide.

Rainfall variability in the Amazon basin is studied in relation to sea-surface temperatures (SSTs) in the equatorial Pacific and the northern and southern tropical Atlantic during the 1977-99 period, using the HiBAm original rainfall data set and complementary cluster and composite analyses.

Considerable evidence has emerged of a substantial decade-long change in the north Pacific atmosphere and ocean lasting from about 1976 to 1988. Observed significant changes in the atmospheric circulation throughout the troposphere revealed a deeper and eastward shifted Aleutian low pressure system in the winter half year which advected warmer and moister air along the west coast of North America and into Alaska and colder air over the north Pacific. Consequently, there were increases in temperatures and sea surface temperatures (SSTs) along the west coast of North America and Alaska but decreases in SSTs over the central north Pacific, as well as changes in coastal rainfall and streamflow, and decreases in sea ice in the Bering Sea. Associated changes occurred in the surface wind stress, and, by inference, in the Sverdrup transport in the north Pacific Ocean. Changes in the monthly mean flow were accompanied by a southward shift in the storm tracks and associated synoptic eddy activity and in the surface ocean sensible and latent heat fluxes. In addition to the changes in the physical environment, the deeper Aleutian low increased the nutrient supply as seen through increases in total chlorophyll in the water column, phytoplankton and zooplankton. These changes, along with the altered ocean currents and temperatures, changed the migration patterns and increased the stock of many fish species. A north Pacific (NP) index is defined to measure the decadal variations, and the temporal variability of the index is explored on daily, annual, interannual and decadal time scales. The dominant atmosphere-ocean relation in the north Pacific is one where atmospheric changes lead SSTs by one to two months. However, strong ties are revealed with events in the tropical Pacific, with changes in tropical Pacific SSTs leading SSTs in the north Pacific by three months. Changes in the storm tracks in the north Pacific help to reinforce and maintain the anomalous circulation in the upper troposphere. A hypothesis is put forward outlining the tropical and extratropical realtionships which stresses the role of tropical forcing but with important feed-backs in the extratropics that serve to emphasize the decadal relative to interannual time scales. The Pacific decadal timescale variations are linked to recent changes in the frequency and intensity of El Niño versus La Nina events but whether climate change associated with “global warming” is a factor is an open question.

Forest fire is of both local and global concern. Large scale fires are not part of the natural disturbance of tropical rain forests but this threat has increased in the last few decades. Under global warming, Indonesia is projected to have higher temperatures and changes in rainfall patterns. Southern Indonesia is predicted to be drier whereas the north is likely to become wetter. Inter-annual climate variability associated with phenomena such as the El Niño Southern Oscillation may cause big decreases in rainfall. This paper reviews the nature and extent of fire problem and the effectiveness of the current policy and institutional provisions in Indonesia in addressing forest fires under projected future climate change. We then consider possible strategies for improving their effectiveness. The review results indicate that first, Indonesia has enacted a number of regulations and established various institutions to tackle forest and other wildfires, but these have proved ineffective. Second, under future climate change scenarios and current fire management practices, Indonesia's tropical rain forests could be more susceptible to fire. Third, effectiveness could be improved by addressing the underlying causes of fires, involving a wide range of stakeholders in formulating the regulations and enhancing law enforcement.► 2-methoxyestradiol as inhibitor of arthritis and osteoporosis.

The main purpose of this work is to provide a broad assessment of the influence of the El Niño–southern oscillation (ENSO) on the frequency of extreme temperature events throughout the year in Argentina. The cold and warm events, defined by the persistence of significant anomalies arising from the maximum and minimum temperatures, are more intense in the subtropical latitudes, north of Argentina (northeast for cold events and northwest for warm events), during the coldest months, and in the south (higher latitudes) in the warmest months. The persistence of the air masses is always greater in the north. The warm (cold) events have a preferential region of dissipation in the northwest (northeast) of Argentina, close to the Andes. The effect of the ENSO phases on the probability of occurrences of these events has a large inter-monthly variability. The different La Niña episodes are more homogeneous in relation to their effects and feasibility for the prediction of extreme temperatures within the region, especially for cold events. During La Niña episodes, all 2 month periods (except August–September) present a higher occurrence probability of very persistent and intense cold events, compared with Neutral months in different regions of the country. Conversely, the different El Niño episodes are more heterogeneous and, therefore, their effects on temperature are more varied and so less predictable. However, El Niño episodes exhibit a stronger signal, which is associated with the tropical air incursions that generate extreme warm events, particularly in winter. These events have a higher occurrence probability in the north and a lower one in the south during the months of June to November. Cold events have a lower occurrence probability in different regions, during the El Niño phase, in the period April to September. In some cases, the ENSO signal is stronger in daily temperature values than in monthly ones over Argentina. Copyright © 2002 Royal Meteorological Society

The tropical Indian Ocean climate variability is investigated using an artificial neural network analysis called self-organizing map (SOM) for both observational data and coupled model outputs. The SOM successfully captures the dipole sea surface temperature anomaly (SSTA) pattern associated with the Indian Ocean Dipole (IOD) and basin-wide warming/cooling associated with ENSO. The dipole SSTA pattern appears only in boreal summer and fall, whereas the basin-wide warming/cooling appears mostly in boreal winter and spring owing to the phase-locking nature of these phenomena. Their occurrence also undergoes significant decadal variation. Composite diagrams constructed for nodes in the SOM array based on the simulated SSTA reveal interesting features. For the nodes with the basin-wide warming, a strong positive SSTA in the eastern equatorial Pacific, a negative Southern Oscillation, and a negative precipitation anomaly in East Africa are found. The nodes with the positive IOD are associated with a weak positive SSTA in the central equatorial Pacific or positive SSTA in the eastern equatorial Pacific, a positive (negative) sea level pressure anomaly in the eastern (western) tropical Indian Ocean, and a positive precipitation anomaly over East Africa. The warming in the central equatorial Pacific appears to correspond to El Niño Modoki discussed recently. These results suggest usefulness of SOM in studying large-scale ocean-atmosphere coupled phenomena.

A 2-year time series (∼ 17-d interval) of zooplankton, sampled from June 1996 through January 1998, along with oceanographic data, allowed the study of species abundances and diversity during non-El Niño and El Niño conditions at Mejillones (23° S) northern Chile. A total of 28 species was identified, of which the most abundant were the calanoids Paracalanus parvus, Calanus chilensis, Acartia tonsa, and Centropages brachiatus, the cyclopoid Oithona similis, and the poecilostomatoids Oncaea conifera and Corycaeus typicus. El Niño Southern Oscillation (El Niño) was first detected in the area in May 1997 and persisted until March 1998. We divided the time series into two parts: non-El Niño conditions. The number of species significantly increased during Eland El Niño conditions, but total abundance of copepods was greater during non-El Niño conditions. Although some expatriate species appeared during El Niño, such as the harpacticoid Microsetella norvegica and Eucalanus subtenuis, the diversity index of Hulburt was not significantly different between the two periods. Despite the dramatic alteration of oceanographic conditions during the El Niño period, we concluded that the community of pelagic copepods was not subject to drastic changes either in total abundance or in structure.

Large-scale coral bleaching was recorded as early as 1931, but severe bleaching on a regional or global scale was not documented until 1983. We use records from a global database of bleaching records to show that severe bleaching events occurred at a global level on four recent occasions and demonstrate that these events occurred in close temporal proximity to a strong negative deviation in the Southern Oscillation Index. While there was no clear increase in the frequency or intensity of major global bleaching events, the number of bleaching records clearly increased during the past three decades. However, increased vigilance and reporting of mild bleaching by an ever-increasing number of researchers and conservation-minded divers has confounded efforts to definitively separate changes in bleaching frequency from changes in reporting.

Tornadoes are a significant hazard in some parts of Canada, particularly in the southern Prairie provinces and southwestern Ontario, though they are not as common as in some parts of the US. Since the early 1980s, the regional weather offices in Canada have been recording tornado event information on a routine basis, and thus data exists that can be used to update older analyses of tornado frequencies. On average, about 60 tornadoes are reported each year, though many doubtless occur that are not observed or recorded in the Environment Canada records. An analysis of tornado frequencies with El Niñ o-Southern Oscillation (ENSO) events suggest that the cooler La Niñ a events tend to suppress tornadic activity, while El Niñ o events tend to enhance it (though there are exceptions to this trend).

1] In this paper, we investigate the atmospheric excitation of polar motion (PM) associated with the El Niño-Southern Oscillation (ENSO) phenomenon. ENSO effects on length-ofday due to changes in the axial component of atmospheric angular momentum (AAM) have long been recognized, but identification of PM excitation with ENSO-induced equatorial AAM anomalies has proved more elusive. Here we use an appropriately modified form of the inverted barometer (IB) assumption to study ENSO-related atmospheric torques arising from pressure loading on the Earth's ellipsoidal bulge and mountains and from frictional wind stress over the Earth's land-and ocean-covered surface. The resulting dissipation torques, which accommodate adjustment of the oceanic mass distribution to time-variable atmospheric loading, are found to be small. The ellipsoidal torques have the largest amplitude, reflecting the order-of-magnitude discrepancy between the height departures of the Earth's bulge (∼20 km) and its surface orography (∼2 km). Because of relatively uniform pressure covariances with the Southern Oscillation Index over the continents for the largely land-based X component and the uniform IB response for the largely ocean-based Y component; however, the ENSO-related PM excitation arising from the ellipsoidal torques is reduced to an amplitude comparable with the sum of regional mountain torques from the individual continents. The largest of these are generated over Asia and Antarctica, arising from efficient coupling of ENSO-related surface pressure anomalies with large-scale orographic features. The geometrical mitigation of the ellipsoidal torques, classically expected to dominate equatorial AAM forcing, accounts for the lack of a detectable atmosphere-driven polar motion response to ENSO.

El Niño-Southern Oscillation (ENSO) plays an important role in the inter-annual variability of rainfall in most parts of southern Africa. The effects of ENSO on the rainy season characteristics and possible impacts on rain-fed maize production were investigated. The rainy season characteristics of concern are the onset of rains, cessation of rains, duration of rainy season and seasonal rainfall total. Rainfall data from 1950 to 2008 for 309 climate stations over the Free State Province were analysed. The rainy season indices for each agricultural year were further subdivided into El Niño and La Niña years. The differences between mean of the rainy season indices were determined for the negative phase of ENSO versus the overall mean and for the positive phase of ENSO versus the overall mean. The results of the onset of rains show no clear pattern in the Free State with some areas experiencing late onset and others early onset in both El Niño and La Niña years. However, the cessation of rains occurs early during the El Niño and later in La Niña years over most parts of the province. Consequently, the duration of the rainy season is shorter than normal in El Niño years and longer than normal in La Niña years. Seasonal rainfall is also lower than normal in El Niño years while in La Niña years more cumulative rainfall is mostly observed. As a result, maize production is favoured in La Niña years and reduction in production is normally observed during El Niño years.

1] The effect of the El Niño/Southern Oscillation (ENSO) on tropical rainfall variations of the past 2 millennia is largely unknown. High-resolution monsoon records are sparse, despite the role of ENSO in generating global hydrologic anomalies in modern climate. To investigate the relationship between ENSO and the Central American Monsoon, we generated a high-resolution ($2.9 years/sample) oxygen-isotope monsoon rainfall record from a U/Th-dated stalagmite (180 B.C. to 1310 A.D.) from the Isthmus of Panama. We present evidence for a weakened monsoon during the ''High Medieval'' (1100-1200 A.D.) and the Classic Maya Collapse (750-950 A.D.). Rainfall decreased and was more variable after 550 A.D., and the period 900-1310 A.D. was drier than the preceding millennium. A weaker monsoon corresponds with increased El Niño variability, and our data display statistical variance in the ENSO band. We conclude that ENSO variation has forced isthmian rainfall and may have contributed to hemispheric climatic anomalies at this time.

Interannual variability in the subsurface tropical Indian Ocean (TIO) is studied using three independent data sets: satellite derived sea level data, an ocean general circulation model simulation, and in situ upper ocean temperature data. It is found that significant interannual variability in the TIO is confined to the north of 15 o S. Unlike the Pacific Ocean, the dominant modes of interannual variability in the Indian Ocean, do not show co−variability between the surface and the subsurface. In contrast to the SST variability dominated by the El Niño and Southern Oscillation (ENSO), subsurface variability is governed by the Indian Ocean Dipole (IOD) in the TIO. The dominant mode of the interannual variability in the subsurface TIO is characterized by a dipole. Its evolution is controlled by equatorial ocean dynamics forced by zonal winds in the equatorial region. It is identified that the subsurface dipole provides the delayed time required to reverse the phase of the surface dipole in the following year. The second dominant mode of interannual variability shows the interesting quasi− biennial tendency. It is found that the turnabout of the phase of the subsurface dipole leads to the quasi−biennial behavior of the TIO. Analysis of in situ subsurface temperature data substantiates this finding. 2 1. Introduction.

Variability and possible teleconnections between annual maximum streamflow from the lower, the middle and the upper Yangtze River basin and El Niño/Southern Oscillation (ENSO) are detected by continuous wavelet transform (CWT), cross-wavelet and wavelet coherence methods. The results show that: (1) different phase relations are found between annual maximum streamflow of the Yangtze River and El Niño/Southern Oscillation (ENSO) in the lower, the middle and the upper Yangtze River basin. In-phase relations are detected between annual maximum streamflow of the lower Yangtze River and anti-phase relations are found in the upper Yangtze River. But ambiguous phase relations occur in the middle Yangtze River, showing that the middle Yangtze River basin is a transition zone. Different climatic systems control the upper and the lower Yangtze River. The upper Yangtze River is mainly influenced by the Indian summer monsoon and the lower Yangtze is mainly influenced by the East Asian summer monsoon; (2) as for the individual stations, different phase relations are found in the longer and the shorter periods, respectively. In the longer periods, the annual maximum streamflow is more influenced by climatic variabilities, while in the shorter periods, it is influenced by other factors, e.g. human activities. The results of the study provide valuable information for improving the long-term forecasting of the streamflow using its relationship with ENSO and the Indian Monsoon. ª

Extensive regions around the world are influenced by the El Niño Southern Oscillation (ENSO). El Niño events occur irregularly but typically once every three to six years 1 . Although the effects of global warming on ENSO oscillations are difficult to predict, recent high resolution climatic models suggest that the frequency of El Niño-like conditions are expected to increase over the coming decades 2 . During an El Niño episode, rainfall dramatically increases in certain areas of the world, whereas severe droughts occur in other regions . The rainfall during El Niño years can be four to ten times higher than average, and the phenomenon lasts approximately one year. The next phase, known as La Niña, produces roughly the opposite climate patterns to those found during an El Niño episode.

Urbanisation has burdened cities with many problems associated with growth and the physical environment. Some of the urban locations in India are becoming increasingly vulnerable to natural hazards related to precipitation and flooding. Thus it becomes increasingly important to study the characteristics of these events and their physical explanation. This work studies rainfall trends in Delhi and Mumbai, the two biggest Metropolitan cities of Republic of India, during the period from 1951 to 2004. Precipitation data was studied on basis of months, seasons and years, and the total period divided in the two different time periods of 1951-1980 and 1981-2004 for detailed analysis. Long-term trends in rainfall were determined by Man-Kendall rank statistics and linear regression. Further this study seeks for an explanation for precipitation trends during monsoon period by different global climate phenomena. Principal component analysis and Singular value decomposition were used to find relation between southwest monsoon precipitation and global climatic phenomena using climatic indices. Most of the rainfall at both the stations was found out to be taking place in Southwest monsoon season. The analysis revealed great degree of variability in precipitation at both stations. There is insignificant decrease in long term southwest monsoon rainfall over Delhi and slight significant decreasing trends for long term southwest monsoon rainfall in Mumbai. Decrease in average maximum rainfall in a day was also indicated by statistical analysis for both stations. Southwest monsoon precipitation in Delhi was found directly related to Scandinavian Pattern and East Atlantic/West Russia and inversely related to Pacific Decadal Oscillation, whereas precipitation in Mumbai was found inversely related to Indian ocean dipole, El Niño-Southern Oscillation and East Atlantic Pattern.

During strong El Niño events, rainfall anomalies and changes in wind patterns are observed in different regions of South America. Along the central Brazilian coast, during the 1983 El Niño year, the frontal systems were blocked to the south, provoking a reversal of the longshore sand transport. Long-duration reversals of longshore transport were also recorded in Holocene beach-ridge terraces from the Rio Doce coastal plain. This led to the formulation of a model relating these reversals of longshore transport to El Niño-like conditions. El Niño-like conditions are past average climate situations that generate the same perturbations as the strong El Niño events observed during the last decade. They are likely to correspond to the long-duration low phase of the Southern Oscillation. To confirm this hypothesis we compared the Holocene beach-ridge record with other palaeoenvironmental records from regions where strong El Niño events would have a substancial signal as well: (1) water-lev...

The three eastern boundary ecosystems comparable to the Benguela ecosystem (BCE) display differences and commonalities. The California (CalCE) and Humboldt Current (HCE) ecosystems are continuous topographically, whereas the Canary Current ecosystem (CanCE) is interrupted by the Gulf of Cadiz and the Canaries archipelago. All have similar regimes of equatorward flow over shelf and slope associated with upwelling and a subsurface poleward flow over the slope, though in the HCE multiple flows and counter-flows appear offshore. All systems exhibit year round upwelling in their centre and seasonal upwelling at their extremes as the trade wind systems that drive them migrate north and south, though the HCE is strongly skewed toward the equator. All systems vary on scales from the event or synoptic scale of a few days, through seasonal, to inter-decadal and long term. Productivity of each system follows the upwelling cycle, though intra-regional variations in nutrient content and forcing cause significant variability within regions. The CanCE is relatively unproductive compared to the CalCE and HCE as a result of differences in large scale circulation between the Pacific and Atlantic. The latter two systems are dominated by El Niño -Southern Oscillation (ENSO) variability on a scale of 4-7 years. Physical modeling with the Princeton Ocean Model and the Regional Oceanic Modeling System has advanced recently to the stage of reproducing realistic mesoscale features and energy levels with climatic wind forcing. Operational forecasting by these models with assimilation of sea surface temperature and other data is successfully implemented in CalCE. On longer time scales, the Lamont-Doherty Earth Observatory model is able to hindcast El Niño variability over the long term up to 2 years in advance. Empirical ecological models in all three systems have attempted prediction of permissible catch level (fractional Maximum Sustainable Yield), recruitment, catches or onset of migration with lack of continued success, partly because discontinuous or inadequate observations hamper model implementation and assessment. Moreover, empirical models tuned to particular environments fail when fundamental regime shifts occur. One of the most successful approaches is that of intensive monitoring of catch and 188 P. Fréon environmental parameters linked to an informal Operational Management Procedure (OMP) to inform fisheries management off Peru. This OMP contributed to preservation of anchovy stock during the 1997-8 El Niño but remains to be formalized or tested under varying conditions. Prediction on time scales of global warming are uncertain because physical climate models still disagree on whether upwelling will intensify or weaken. Possible scenarios on decadal scale based on warming or cooling of waters in the Eastern Boundary Current systems can be proffered, albeit with little confidence at present. Future approaches for all systems, including the BCE, will in the long run likely combine coupled atmospheric/ocean models with biological process models. Judicious application of purely statistical modeling based on inherent time series properties will assist, though such techniques are unable to cope with regime shifts.

The eponym "Walker Circulation" refers to a concept used by atmospheric scientists and oceanographers in providing a physical explanation for the El Niño-Southern Oscillation phenomenon, whereas the eponym "Yule-Walker equations" refers to properties satisfied by the autocorrelations of an autoregressive process. But how many statisticians (or, for that matter, atmospheric scientists) are aware that the "Walker" in both terms refers to the same individual, Sir Gilbert Thomas Walker, and that these two appellations arose in conjunction with the same research on the statistical prediction of climate? Like George Udny Yule (the "Yule" in Yule-Walker), Walker's motivation was to devise a statistical model that exhibited quasiperiodic behavior. The original assessments of Walker's work, both in the meteorology and in statistics, were somewhat negative. With hindsight, it is argued that his research should be viewed as quite successful.

1] Using observed data sets mainly for the period 1979-2005, we find that anomalous warming events different from conventional El Niño events occur in the central equatorial Pacific. This unique warming in the central equatorial Pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly (SSTA) on both sides along the equator. empirical orthogonal function (EOF) analysis of monthly tropical Pacific SSTA shows that these events are represented by the second mode that explains 12% of the variance. Since a majority of such events are not part of El Niño evolution, the phenomenon is named as El Niño Modoki (pseudo-El Niño) (''Modoki'' is a classical Japanese word, which means ''a similar but different thing''). The El Niño Modoki involves ocean-atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution, analogous to the Southern Oscillation in the case of El Niño. Hence the total entity is named as El Niño-Southern Oscillation (ENSO) Modoki. The ENSO Modoki events significantly influence the temperature and precipitation over many parts of the globe. Depending on the season, the impacts over regions such as the Far East including Japan, New Zealand, western coast of United States, etc., are opposite to those of the conventional ENSO. The difference maps between the two periods of 1979-2004 and 1958-1978 for various oceanic/atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline. This appears to be a cause of more frequent and persistent occurrence of the ENSO Modoki event during recent decades.

This report documents the extent to which coral colonies show fluctuations in their associations with different endosymbiotic dinoflagellates. The genetic identity of Symbiodinium from six coral species [Acropora palmata (Lamarck), A. cervicornis (Lamarck), Siderastrea siderea (Ellis and Solander), Montastrea faveolata (Ellis and Solander), M. annularis (Ellis and Solander), and M. franksi (Gregory)] was examined seasonally over five years (1998 and 2000–2004) in the Bahamas and Florida Keys at shallow (1 to 4 m) fore-reef/patch reef sites and at deeper fore-reef (12–15 m) locations. Symbionts were identified genetically using denaturing gradient gel electrophoresis (DGGE) fingerprinting of the internal transcribed spacer region 2 (ITS2) of ribosomal RNA gene loci. Repetitive sampling from most labeled colonies from the Bahamas and the Florida Keys showed little to no change in their dominant symbiont. In contrast, certain colonies of M. annularis and M. franksi from the Florida Keys exhibited shifts in their associations attributed to recovery from the stresses of the 1997–1998 El Niño southern oscillation (ENSO) event. Over several years, a putatively stress-tolerant clade D type of Symbiodinium was progressively replaced in these colonies by symbionts typically found in M. annularis and M. franksi in Florida and at other Caribbean locations. Greater environmental fluctuations in Florida may explain the observed changes among some of the symbioses. Furthermore, symbiotic associations were more heterogeneous at shallow sites, relative to deep sites. The exposure to greater environmental variability near the surface may explain the higher symbiont diversity found within and between host colonies.

Summer monsoon rains are a critical factor in Thailand’s water resources and agricultural planning and management. In fact, they have a significant impact on the country’s economic health. Consequently, understanding the variability of the summer monsoon rains over Thailand is important for instituting effective mitigating strategies against extreme rainfall fluctuations. To this end, the authors systematically investigated the relationships between summer monsoon precipitation from the central and northern regions of Thailand and large-scale climate features. It was found that Pacific sea surface temperatures (SSTs), in particular, El Niño–Southern Oscillation (ENSO), have a negative relationship with the summer monsoon rainfall over Thailand in recent decades. However, the relationship between summer rainfall and ENSO was weak prior to 1980. It is hypothesized that the ENSO teleconnection depends on the SST configuration in the tropical Pacific Ocean, that is, an eastern Pacific–b...

We investigate the viability of using El Niño-Southern Oscillation (ENSO) and sea surface temperature (SST) data to predict seasonal streamflow for one of the major rivers in Sri Lanka, the Kelani, using correlation analysis, contingency tables, and principal component analysis. The agricultural seasons in Sri Lanka are Yala (April-September) and Maha (October-March). The correlation between the Kelani River streamflow during Yala and ENSO indices (r = À0.41) is significant at 99% level. In addition, the Kelani streamflow during Yala has a correlation with the Central Indian Ocean SST (r = À0.40) that is also significant at the 99% level. The first principal component of the Indo-Pacific Ocean SST is reminiscent of the SST associated with the ENSO mode. A prediction scheme based on this mode for the streamflow during Yala has a skill characterized by a correlation of 0.5 in a cross-validated mode.

An extensive outbreak of dengue fever and dengue hemorhagic fever occurred in the city of Palembang, South Sumatra, Indonesia from late 1997 through March/April 1998. All surveyed administrative areas (kelurahan) in Palembang were found to be &#39;permissive&#39; for dengue virus transmission; and all areas that had Aedes (subgenus Stegomyia) larval mosquitoes in abundance experienced increased cases of DHF during the epidemic. The Aedes House Index (HI) for combined Aedes aegypti and Aedes albopictus was recorded every 3 months before, during, and after the epidemic. Ten surveyed sentinel sites (October-December 1997) immediately preceding the epidemic peak had a combined HI of 25% (range 10-50.8%). Entomological surveys during the peak epidemic period (January-April) showed a combined HI of 23.7% (range: 7.6-43.8%). Kelurahans with the highest numbers of reported dengue cases had an HI exceeding 25%; however, there was no discernable relationship between elevated HI and increased ...

The Southern Hemisphere westerlies in the southwest Pacific are known to have waxed and waned numerous times during the last two glacial cycles, though even semi-continuous histories of the westerlies extend back no more than about 20,000 years. We have good evidence for at least three scales of events.

The climate of Labrador is uniquely influenced by Labrador Sea atmosphere-ocean dynamics and related sea surface temperature, sea ice and atmospheric fluctuations in the northwest Atlantic. Here we describe composite ring width and maximum latewood density white spruce records averaged over five (four for density) treeline sites in northern Labrador, spanning the past four centuries. These records correlate significantly with surface air and sea surface temperature records for the northwest Atlantic as well as with the North Atlantic Oscillation (NAO). Temperatures over Labrador appear to have been influenced by climate processes operating on interannual to multidecadal time scales over the length of the tree-ring record. The ring width composite reveals a significant (>99% level) mode of variation centered at around 40-60 years which appears to be robust over the full length of record and may correspond to multidecadal modes identified in model and instrumental studies of North Atlantic climate. The density composite indicates significant peaks at about 21-24, 9 and 2-3 years, which generally correspond to spectral modes identified for the NAO. This density series also shows a significant (>99% level) mode of variation at 3.6 years, which is statistically coherent with the winter (DJF) Southern Oscillation Index. This mode decreases in amplitude in the 1800s period of the Little Ice Age, one of the lowest growth periods in the Labrador tree-ring series as well as other northern temperature proxies. This period was also a time of diminished solar activity and several major volcanic events, including the eruption of Tambora in 1815. The ensuing summer of 1816 was the coldest over the past four centuries as inferred from the Labrador density composite. Hardships suffered by Labrador Inuit resulting from the extreme cold period of 1816-17 are mentioned in Moravian mission records. Archaeological and ethnohistorical data also document shifts in the subsistence practices and settlement patterns of Labrador Inuit throughout the 1800s. Many of the cultural changes have been attributed to the effects of European settlement of the region, but may also be a response to the severe climatic conditions during this time.

Marquesas archipelago drowned reefs biological assemblages sea-level changes deglacial sea-level rise Bathymetric surveys of submarine platforms and terraces of the tropical Marquesas archipelago (French Polynesia), coupled with sedimentological and paleoecological analyses and radiometric dating of dredged rocks, reveal the occurrence of several distinct intervals of reef deposition during the last deglacial sea-level rise (i.e. the last 26,000 yr or 26 ky). Five facies related to reef, shallow-water and deeper depositional zones have been identified, on the basis of their respective biological assemblages. Facies 1, 2 and 3 consist of in situ scleractinian corals (mainly Porites) associated with thick crusts of coralline algae species, Hydrolithon onkodes, H. reinboldii, Lithophyllum pustulatum group, and widespread vermetids and victoriellinid foraminifers. These assemblages are typical of high-energy, shallow-water reef settings (i.e. upper forereef, reef crest and outer reef flat, and inner reef flat respectively). Facies 4 is characterized by the prevalence of Halimeda plates, mixed with debris of Amphiroa and Amphistegina spp.; these algae generally inhabit the inner parts of the reef flat and backreef zones but also the relatively protected, deeper parts of outer reef slopes. Facies 5 is composed of large broken mollusc shells (oysters), embedded in fine-grained sediments with significant numbers of deep-living coralline algae Mesophyllum sp., and planktonic foraminifers. Locally, mollusc shells are covered with microbialite crusts. The replacement of shallower assemblages by deeper ones is interpreted as an upward-deepening sequence. Identification of morphological and biological features combined with coral dating provide evidence of 4 reef generations (RG) between 26 and 9 ka, now ranging from 138 to 58 m in depth: 1) RG 0 from 26 to 19 ka in the 125-115 m depth interval; 2) RG 1 from 18 to 15 ka between 110 and 95 m; 3) RG 2 from 14 to 11.5 ka between 80 and 68 m; and 4) RG 3 younger than 11.5 ka, at around 55 to 60 m. The first three units exhibit clear zonation, from upper reef slope to reef flat. Their development was probably interrupted by abrupt rises in sea-level and/or drastic climate changes. Such a scenario is similar to observations reported in Barbados and Hawai'i where rapid rises in sea-level, interpreted as reflecting major melting events of continental ice, caused the drowning of reefs. The younger unit refers to coral banks similar to those in modern Marquesas environments. The replacement of typical coral reefs by coral banks may reflect an increase El Niño-Southern Oscillation (ENSO) frequency and intensity inimical to reef development in the last 12 ka.

This paper investigates the variability of sea surface salinity (SSS) in the western equatorial Pacific fresh pool. For this purpose, we processed data collected from thermosalinographs embarked on merchant ships. Two main cross-equatorial shipping lines that are representative of the oceanic conditions in the western tropical Pacific were selected: the Japan-Tarawa-Fiji line that crosses the equator near 173øE (eastern track) and the New-Caledonia-Japan line that crosses the equator near 156øE (western track). We show that there is a strong SSS variability in the region at monthly as well as interannual timescales. This high variability is attributed to the successive passages of a zonal salinity front, trapped in the (5øN-5øS) equatorial band and migrating in phase with the southern oscillation index. We also found the eastern track to be more variable in SSS because it is more exposed to these SSS front incursions. We carried out a detailed study of the mechanisms responsible for this variability; it revealed that the rainfall input acts as a source of freshwater responsible for the existence of a contrasted distribution of SSS (mainly high-salinity waters in the central Pacific and low-salinity waters in the western Pacific). However, the main mechanism responsible for the SSS variability is zonal advection that makes the two distinct masses of water converge, resulting in a salinity front which shifts back and forth in the equatorial band. 2Now at Laboratoire d'Oceanographie Dynamique et du Climat, Paper number 97JC01773. 0148-0227/98/97JC-01773509.00 contribution in E1 Nifio-Southern Oscillation (ENSO) dynamics. The thin surface lens of relatively fresh waters that we call Western Pacific Fresh Pool seems to behave as if it slides on top of the region, responding to wind changes within days [Lukas, 1988]. Close to the equator, horizontal distribution of sea surface salinity (SSS) is also potentially significant as it reveals a surface salinity front at the eastern edge of the warm pool. The front marks a boundary between western and central Pacific surface waters. The western equatorial and tropical waters are characterized by low surface salinity due to excess of precipitation over evaporation most of the time, while evaporation dominates east of the fresh pool leading to saltier waters in the central Pacific enhanced by equatorial upwelling processes. In climatologies, salinity data show evidence of the front [Levitus, 1982], but no such evidence can be derived from wind forcing, buoyancy, or temperature data. Under wind convergence zones, SSS distribution is mainly driven by the evaporation-minus-precipitation budget, with a time lag of a few months. This process does not prevail in the western equatorial Pacific [Delcroix et al., 1996]. Sprintall and McPhaden [1994] discussed the importance of zonal advection of salinity along the equator using long moored time series data from 0 ø, 165øE. The role of zonal advection was recently emphasized by Shinoda and Lukas [1995], H•nin et al. [1995] and Picaut et al. [1996]. Positive advection of low-salinity water from the western Pacific is a result of eastward currents in the equatorial band, due to eastward jets generated either by westerly wind bursts or by positive horizontal zonal salinity gradients, i.e., "fresh equatorial jets" which have already been observed near the date line in the western Pacific [Roemmich et al., 1994]. Several studies have emphasized the influence of salinity on tropical ocean model simulations [Cooper, 1988] and the influ-7523 10"S 1 J FHAMJ JASOND 0_ 1 178E Plate 2. Time-latitude sea surface salinity measured by thermosalinograph for the 1992-1995 period, along the (top) western track, (middle) along the eastern track. The different voyages are indicated by lines. (bottom) SOl filtered with a 6-month Hanning filter over the same period.