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ENSO Events (enso + event)
Selected AbstractsENSO and the South China Sea summer monsoon onsetINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 2 2007Wen Zhou Abstract This paper investigates the relationship between the onset date of the South China Sea summer monsoon (SCSSM) and the El Niño/Southern Oscillation (ENSO). The monsoon onset date (MOD) is defined on the basis of the switch of the 850-hPa zonal winds over the South China Sea (SCS) from easterly to westerly for two consecutive pentads. The ENSO signal is represented by the ocean heat content (OHC), which is proportional to the depth of the 20 °C isotherm. It is found that, in years associated with a warm (cold) ENSO event or the year after, the monsoon tends to have a late (an early) onset and the intensity of the SCSSM also tends to be weaker (stronger). During a 2-year period prior to the onset, anomalies of OHC have an obvious eastward propagation. The 850-hPa flow east of the Philippines, specifically the strength of the subtropical high, is also found to be critical in determining the MOD. The link between these two results appears to be the propagation of cold (warm) subsurface water into the western North Pacific (WNP), which strengthens (weakens) the subtropical high, and hence a late (an early) SCSSM onset. Copyright © 2006 Royal Meteorological Society. [source] El Niño,southern oscillation events and associated European winter precipitation anomaliesINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 1 2005D. Pozo-Vázquez Abstract The winter precipitation anomalies in the European area have been analysed over the period 1900,98 based on the El Niño,Southern oscillation (ENSO) state. A set of winter and autumn ENSO events is first selected using the Sea-Surface temperature (SST) data of the Niño 3 region, with the constraint that the ENSO event is well developed during the winter and autumn of study, and that it is an extreme event. Cold and warm ENSO events and periods that can be regarded as normal are selected. For the selected winter ENSO events and for the winter following the selected autumn ENSO events, composites of European winter precipitation anomalies have been obtained and compared with each other. A study of the consistency among events of the relationship between ENSO and precipitation anomalies was also carried out. The analysis of the winter precipitation anomalies based on the selected winter ENSO events shows the existence, for the European area and during La Niña events, of a statistically significant precipitation anomaly pattern with positive precipitation anomalies north of the British Isles and in the Scandinavian area and negative anomalies in southern Europe, resembling the precipitation pattern associated with the positive phase of the North Atlantic oscillation (NAO). Particularly, for the southwestern area of the Iberian Peninsula, the negative anomaly reaches 20% of the winter average precipitation. The consistency analysis shows that this precipitation pattern is not the result of a few major events, but rather that it is stable and qualitatively similar to that found during the positive phase of the NAO. A non-linear response to ENSO is found in the eastern Mediterranean area: negative precipitation anomalies are found, having similar amplitude anomalies, both during El Niño and La Niña events. The analysis of the precipitation anomalies for the winter following the selected autumn ENSO events shows very similar results to those found for the previous analysis, thus suggesting the existence of a potential source of seasonal forecasting of European precipitation. An analysis of the sensitivity of the precipitation anomalies to the strength of the ENSO events shows that, when the strength of the ENSO increases, the magnitude of the rainfall anomalies does not change, but the area influenced and the coherence between events do increase slightly. Copyright © 2005 Royal Meteorological Society [source] Variable strength of top-down effects in Nothofagus forests: bird predation and insect herbivory during an ENSO eventAUSTRAL ECOLOGY, Issue 4 2009C. NOEMI MAZIA Abstract Predators are thought to play a key role in controlling herbivory, thus having positive indirect effects on plants. However, evidence for terrestrial trophic cascades is still fragmentary, perhaps due to variation in top-down forces created by environmental heterogeneity. We examined the magnitude of predation effects on foliar damage by chewing insects and mean leaf size, by excluding birds from saplings in ,dry' and ,wet'Nothofagus pumilio forests in the northern Patagonian Andes, Argentina. The experiment lasted 2 years encompassing a severe drought during the La Niña phase of a strong El Niño/Southern Oscillation event, which was followed by unusually high background folivory levels. Insect damage was consistently higher in wet than in dry forest saplings. In the drought year (1999), bird exclusion increased folivory rates in both forests but did not affect tree leaf size. In the ensuing season (2000), leaf damage was generally twice as high as in the drought year. As a result, bird exclusion not only increased the extent of folivory but also significantly decreased sapling leaf size. The latter effect was stronger in the wet forest, suggesting compensation of leaf area loss by dry forest saplings. Overall, the magnitude of predator indirect effects depended on the response variable measured. Insectivorous birds were more effective at reducing folivory than at facilitating leaf area growth. Our results indicate that bird-initiated trophic cascades protect N. pumilio saplings from insect damage even during years with above-normal herbivory, and also support the view that large-scale climatic events influence the strength of trophic cascades. [source] Long-term reproductive behaviour of woody plants across seven Bornean forest types in the Gunung Palung National Park (Indonesia): suprannual synchrony, temporal productivity and fruiting diversityECOLOGY LETTERS, Issue 10 2007Charles H. Cannon Abstract For 68 months, we observed the reproductive behaviour of 7288 woody plants (172 figs, 1457 climbers and 5659 trees) spanning major soil and elevational gradients. Two 2,3 month community-wide supra-annual fruiting events were synchronized across five forest types, coinciding with ENSO events. At least 27 genera in 24 families restricted their reproduction to these events, which involved a substantial proportion of tree diversity (> 80% of phylogenetic diversity). During these events, mean reproductive levels (8.5%) represented an almost four-fold increase compared with other months. These patterns indicate a strong behavioural advantage to this unusual reproductive behaviour. Montane forest experienced a single, separate fruiting peak while the peat swamp forest did not participate. Excluding these events, no temporal reproductive pattern was detectible, at either the landscape or forest type. These phenological patterns have major implications for the conservation of frugivore communities, with montane and swamp forests acting as ,keystone' forests. [source] El Niño, climate change, and Southern African climateENVIRONMETRICS, Issue 4 2001Simon J. Mason Abstract The El Niño phenomenon involves a large-scale warming of the equatorial eastern and central Pacific Ocean. Recent developments in the El Niño,Southern Oscillation (ENSO) phenomenon have raised concerns about climate change. In this review paper, these recent developments are critically assessed and forecasts of possible future changes are reviewed. Since the late-1970s, El Niño episodes have been unusually recurrent, while the frequency of strong La Niña events has been low. Prolonged/recurrent warm event conditions of the first half of the 1990s were the result of the persistence of an anomalously warm pool near the date line, which, in turn, may be part of an abrupt warming trend in tropical sea-surface temperatures that occurred in the late-1970s. The abrupt warming of tropical sea-surface temperatures has been attributed to the enhanced-greenhouse effect, but may be indicative of inter-decadal variability: earlier changes in the frequency of ENSO events and earlier persistent El Niño and La Niña sequences have occurred. Most forecasts of ENSO variability in a doubled-CO2 climate suggest that the recent changes in the tropical Pacific are anomalous. Of potential concern, however, is a possible reduction in the predictability of ENSO events given a warmer background climate. El Niño events usually are associated with below-normal rainfall over much of southern Africa. Mechanisms for this influence on southern African climate are discussed, and the implications of possible changes in ENSO variability on the climate of the region are assessed. Recent observed changes in southern African climate and their possible relationships with trends in ENSO variability are investigated. The El Niño influence on rainfall over southern Africa occurs largely because of a weakening of tropical convection over the subcontinent. A warming of the Indian Ocean during El Niño events appears to be important in providing a teleconnection from the equatorial Pacific Ocean. The abrupt warming of the tropical Pacific and Indian oceans in the late-1970s is probably partly responsible for increasing air temperatures over southern Africa, and may have contributed to a prolongation of predominantly dry conditions. A return to a wet phase appears to have occurred, despite the persistence of anomalously high sea-surface temperatures associated with the late-1970s warming, and a record-breaking El Niño in 1997/98. Copyright © 2001 John Wiley & Sons, Ltd. [source] Time series analyses reveal transient relationships between abundance of larval anchovy and environmental variables in the coastal waters southwest of TaiwanFISHERIES OCEANOGRAPHY, Issue 2 2009CHIH-HAO HSIEH Abstract We investigated environmental effects on larval anchovy fluctuations (based on CPUE from 1980 to 2000) in the waters off southwestern Taiwan using advanced time series analyses, including the state-space approach to remove seasonality, wavelet analysis to investigate transient relationships, and stationary bootstrap to test correlation between time series. For large-scale environmental effects, we used the Southern Oscillation Index (SOI) to represent the El Niño Southern Oscillation (ENSO); for local hydrographic conditions, we used sea surface temperature (SST), river runoff, and mixing conditions. Whereas the anchovy catch consisted of a northern species (Engraulis japonicus) and two southern species (Encrasicholina heteroloba and Encrasicholina punctifer), the magnitude of the anchovy catch appeared to be mainly determined by the strength of Eng. japonicus (Japanese anchovy). The main factor that caused the interannual variation of anchovy CPUE might change through time. The CPUE showed a negative correlation with combination of water temperature and river runoff before 1987 and a positive correlation with river runoff after 1988. Whereas a significant negative correlation between CPUE and ENSOs existed, this correlation was driven completely by the low-frequency ENSO events and explained only 10% of the variance. Several previous studies on this population emphasized that the fluctuations of larval anchovy abundance were determined by local SST. Our analyses indicated that such a correlation was transient and simply reflected ENSO signals. Recent advances in physical oceanography around Taiwan showed that the ENSOs reduced the strength of the Asian monsoon and thus weakened the China Coastal Current toward Taiwan. The decline of larval anchovy during ENSO may be due to reduced China Coastal Current, which is important in facilitating the spawning migration of the Japanese anchovy. [source] Modeling the influence of oceanic-climatic changes on the dynamics of Pacific saury in the northwestern Pacific using a life cycle modelFISHERIES OCEANOGRAPHY, Issue 2004YONGJUN TIAN Abstract A life cycle model for Pacific saury (Cololabis saira) was developed to clarify the possible causes of interannual and decadal variability in its abundance. In the model, the population of saury is composed of two spawning cohorts: one spawned in the Kuroshio region during autumn,winter and the other spawned in the Kuroshio-Oyashio Transition Zone during winter,spring. The life cycle of saury was divided into six stages: namely egg, larval, juvenile, young, immature and adult stages. The life cycle model combines growth, survival, fishing and reproductive processes, in which the effects of sea surface temperature (SST) in the Kuroshio region and El Niño-Southern Oscillation (ENSO) events on the winter-spawning cohorts, the effects of SST in the Oyashio region on the spring-spawning cohorts, and the effects of fishing on the two spawning cohorts are taken into account. Results of basic modeling, in which environments are assumed stable and the stock is affected by fishing only, shows that the interannual fluctuations in the abundance are small and could hardly explain the observed large annual changes in abundance. On the contrary, results of modeling incorporating the effects of oceanic-climatic changes corresponded well with actual interannual-decadal variations in abundance. These results suggest the following environmental effects: (1) SST in the Kuroshio region affects decadal changes in abundance; (2) ENSO events influence the survival of the winter spawning cohort and result in large interannual variations in the abundance. It is concluded that large-scale climatic and oceanic changes strongly affect the abundance of saury. [source] Implications of interannual variability in euphausiid population biology for fish production along the south-west coast of Vancouver Island: a synthesisFISHERIES OCEANOGRAPHY, Issue 1 2002R. W. Tanasichuk This is a synthesis of published and unpublished research on euphausiid and fish populations using the south-west coast of Vancouver Island. Overall, the studies covered 1985,98, when there were two ENSO events and considerable variation in upwelling. The population biology of the dominant euphausiids (Thysanoessa spinifera, Euphausiapacifica) was monitored during 1991,98. The species abundance trends differed. Results of simple correlation analyses suggested that variations in temperature, salinity and upwelling do not explain variations in the abundance of larval or adult euphausiids, or in the abundance of portions of euphausiid populations on which fish feed. I found significant interannual variations in daily ration of the dominant planktivorous fish species, but euphausiids remained the most important prey. Pacific hake (Merluccius productus), the dominant planktivore, fed on larger (>17 mm) T. spinifera, even though the biomass of this part of the euphausiid biomass decreased by 75% between 1991 and 1997, but Pacific herring (Clupea pallasi) may have begun feeding on smaller E. pacifica. Therefore, any study of the relationship between fish production and krill biology must consider that part of the euphausiid biomass exploited by fish. In addition, some fish species and/or life history stages appeared to adapt to changes in euphausiid availability, while others did not. Such variation in adaptations also has to be described and considered to understand how changes in euphausiid biology affect fish productivity. [source] Herbivory and plant growth rate determine the success of El Niño Southern Oscillation-driven tree establishment in semiarid South AmericaGLOBAL CHANGE BIOLOGY, Issue 12 2006MILENA HOLMGREN Abstract While climatic extremes are predicted to increase with global warming, we know little about the effect of climatic variability on biome distribution. Here, we show that rainy El Niño Southern Oscillation (ENSO) events can enhance tree recruitment in the arid and semiarid ecosystems of north-central Chile and northwest Peru. Tree-ring studies in natural populations revealed that rainy El Niño episodes have triggered forest regeneration in Peru. Field experiments indicate that tree seedling recruitment in Chile is much less successful than in Peru due mostly to larger mortality caused by herbivores. The dramatic impact of herbivores in Chile was derived from the combined result of slower plant growth and the presence of exotic herbivores (European rabbits and hares). The interplay of herbivory and climatic effects we demonstrated implies that rainy ENSO events may represent ,windows of opportunity' for forest recovery if herbivore pressure is minimized at the right moment. [source] Climatic signals in growth and its relation to ENSO events of two Prosopis species following a latitudinal gradient in South AmericaGLOBAL CHANGE BIOLOGY, Issue 5 2006BERNAT C. LÓPEZ Abstract Semiarid environments throughout the world have lost a major part of their woody vegetation and biodiversity due to the effects of wood cutting, cattle grazing and subsistence agriculture. The resulting state is typically used for cattle production, but the productivity of these systems is often very low, and erosion of the unprotected soil is a common problem. Such dry-land degradation is of great international concern, not only because the resulting state is hardly productive but also because it paves the way to desertification. The natural distribution of the genus Prosopis includes arid and semiarid zones of the Americas, Africa and Asia, but the majority of the Prosopis species are, however, native to the Americas. In order to assess a likely gradient in the response of tree species to precipitation, temperature and their connection to El Niño southern oscillation (ENSO) events, two Prosopis species were chosen along a latitudinal gradient in Latin America, from northern Peru to central Chile: Prosopis pallida from a semi-arid land in northern and southern Peru and P. chilensis from a semiarid land in central Chile. Growth rings of each species were crossdated at each sampling site using classical dendrochronological techniques. Chronologies were related with instrumental climatic records in each site, as well as with SOI and N34 series. Cross-correlation, spectral and wavelet analysis techniques were used to assess the relation of growth with precipitation and temperature. Despite the long distance among sites, the two Prosopis species presented similar responses. Thus, the two species' growth is positively correlated to precipitation, while with temperature it is not. In northern Peru, precipitation and growth of P. pallida present a similar cyclic pattern, with a period of around 3 years. On the other hand, P. pallida in southern Peru, and P. chilensis also present this cyclic pattern, but also another one with lower frequency, coinciding with the pattern of precipitation. Both cycles are within the range of the ENSO band. [source] El Niño Southern Oscillation link to the Blue Nile River Basin hydrologyHYDROLOGICAL PROCESSES, Issue 26 2009Wossenu Abtew Abstract The objective of this study is to evaluate the relationships of El Niño Southern Oscillation (ENSO) indices and the Blue Nile River Basin hydrology using a new approach that tracks cumulative ENSO indices. The results of this study can be applied for water resources management decision making to mitigate drought or flood impacts with a lead time of at least few months. ENSO tracking and forecasting is relatively easier than predicting hydrology. ENSO teleconnections to the Blue Nile River Basin hydrology were evaluated using spatial average basin rainfall and Blue Nile flows at Bahir Dar, Ethiopia. The ENSO indices were sea surface temperature (SST) anomalies in region Niño 3·4 and the Southern Oscillation Index (SOI). The analysis indicates that the Upper Blue Nile Basin rainfall and flows are teleconnected to the ENSO indices. Based on event correspondence and correlation analysis, high rainfall and high flows are likely to occur during La Niña years and dry years are likely to occur during El Niño years at a confidence level of 90%. Extreme dry and wet years are very likely to correspond with ENSO events as given above. The great Ethiopian famine of 1888,1892 corresponds to one of the strongest El Niño years, 1888. The recent drought years in Ethiopia correspond to strong El Niño years and wet years correspond to La Niña years. In this paper, a new approach is proposed on how to classify the strength of ENSO events by tracking consecutive monthly events through a year. A cumulative SST index value of ,5 and cumulative SOI value of , ,7 indicate strong El Niño. A cumulative SST index value of ,,5 and cumulative SOI index of ,7 indicate strong La Niña. Copyright © 2009 John Wiley & Sons, Ltd. [source] China's snow disaster in 2008, who is the principal player?INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 14 2009Gao Hui Abstract The unprecedented snow disaster in January 2008 brought serious human and economic losses to China. It has been suggested that the La Nina event is the principal cause. But analysis indicates that in December 2007, the circulation patterns in the tropical regions are quite similar with those in January 2008. In contrast large differences existed at high latitudes, especially the Siberia high (SH) and the north polar vortex (NPV). The differences can also be found between other extreme heavy and light snow years. In the extreme heavy (light) snow years, the SH is stronger (weaker) and the NPV is deeper (shallower). But these extreme snow events don't correspond to ENSO events well. Statistical results also indicate that both the SH and the NPV are independent of ENSO. So, rather than the La Nina event, the abnormal circulations at the high latitudes may play a more crucial role in making this snow disaster. Copyright © 2009 Royal Meteorological Society [source] Multi-annual dry episodes in Australian climatic variabilityINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 12 2009B. G. Hunt Abstract The output from a 10 000-year simulation with the CSIRO Mark 2 coupled global climatic model has been analysed to investigate the occurrence of multi-year dry episodes for three selected regions of Australia, specifically, the northeast, southeast and southwest of the continent. Results are presented for dry episodes lasting for 8 or more years. An episode is defined as a time interval having consecutive negative rainfall anomalies, but not necessarily a major drought, for each year of the episode. The hydrological consequences of such an episode can persist for over a century. Typically about 30 episodes are found over the 10 000 years of the simulation for each of the three regions. There is little synchronicity between the regions in the occurrence of the dry episodes. While there is an El Nino/Southern Oscillation (ENSO) influence associated with these episodes, it is not continuous over the duration of an episode. Composites of sea surface temperature anomalies over an episode highlight the limited presence of ENSO events. The occurrence of the dry episodes for all three regions is essentially random, with multi-centennial periods without an episode, and episodes at multi-decadal frequency at other times. Following a discussion of possible mechanistic influences, it is concluded that stochastic forcing is responsible for the occurrence of dry episodes. This implies that there is no predictability associated with the initiation, duration or termination of individual dry episodes. This also suggests that the 2000,2007 dry episodes occurring over much of Australia may not be caused by the greenhouse effect. Such an episode has a return period of between 200 and 300 years based on the mean frequency of occurrence in the present simulation. Copyright © 2008 Royal Meteorological Society [source] On ENSO impacts on European wintertime rainfalls and their modulation by the NAO and the Pacific multi-decadal variability described through the PDO indexINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 8 2008Davide Zanchettin Abstract While strong relationships have previously been established between the El Niño/Southern Oscillation (ENSO) and climate variability in many parts of the world, previous analyses of ENSO impacts on European rainfalls have been variable and inconclusive. In this paper, the role and apparent interactions of a range of known teleconnections are assessed. It is shown that ENSO events do indeed appear to impact European rainfalls and that these impacts are likely to also depend on the concurrent state of the North Atlantic Oscillation (NAO) and the Pacific Decadal Oscillation (PDO). In particular, it is demonstrated that ENSO impacts most significantly on European wintertime rainfalls during positive (warm) phases of the PDO. Copyright © 2007 Royal Meteorological Society [source] Classification of synchronous oceanic and atmospheric El Niño-Southern Oscillation (ENSO) events for palaeoclimate reconstructionINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 12 2005Joëlle L. Gergis Abstract Since the mid-1970s, ENSO has changed in character to a predominance of El Niño conditions, the extreme phase of which appears coincidental with increases in global temperature records. Instrumental time series (<150 years) are too short to adequately address the significance of late twentieth-century ENSO variability, thus, multi-century palaeoclimate reconstructions derived from long proxy records are sought. Despite the global influence exerted by ENSO on society, limited consensus exists within the scientific community as to which index best defines the timing, duration and strength of events. Here we address issues associated with the complexity of ENSO characterisation by comparing the ,event capture' ability of two currently used indices of ENSO. It is suggested that the use of a sole ENSO index is undesirable as a given index is only indicative of one physical aspect of the phenomenon, and as such is unlikely to be representative of the wider interactions experienced in the coupled ocean-atmospheric system. In an attempt to describe more of the nature and evolution of ENSO events, the Coupled ENSO Index (CEI) classification scheme was devised to identify synchronous oceanic (Niño 3.4 SST) and atmospheric (Southern Oscillation Index) anomalies associated with ENSO for the instrumental period (1871,2003). The CEI is of practical relevance to the ENSO community as it provides an amplitude preserving instrumental baseline for the calibration of proxy records to reconstruct both components of the ENSO system. Analysis of the nature of instrumental ENSO events from the CEI suggests that the frequency and intensity of post-1970 ENSO events (when 50% of all extreme events identified occur) appears the most anomalous in the context of at least the past century. It is hoped that the CEI will facilitate palaeo-ENSO research to systematically resolve the long-term context of past ENSO behaviour to assess whether the apparently anomalous nature of late twentieth-century variability is unprecedented within existing palaeoclimate archives. Copyright © 2005 Royal Meteorological Society. [source] El Niño,southern oscillation events and associated European winter precipitation anomaliesINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 1 2005D. Pozo-Vázquez Abstract The winter precipitation anomalies in the European area have been analysed over the period 1900,98 based on the El Niño,Southern oscillation (ENSO) state. A set of winter and autumn ENSO events is first selected using the Sea-Surface temperature (SST) data of the Niño 3 region, with the constraint that the ENSO event is well developed during the winter and autumn of study, and that it is an extreme event. Cold and warm ENSO events and periods that can be regarded as normal are selected. For the selected winter ENSO events and for the winter following the selected autumn ENSO events, composites of European winter precipitation anomalies have been obtained and compared with each other. A study of the consistency among events of the relationship between ENSO and precipitation anomalies was also carried out. The analysis of the winter precipitation anomalies based on the selected winter ENSO events shows the existence, for the European area and during La Niña events, of a statistically significant precipitation anomaly pattern with positive precipitation anomalies north of the British Isles and in the Scandinavian area and negative anomalies in southern Europe, resembling the precipitation pattern associated with the positive phase of the North Atlantic oscillation (NAO). Particularly, for the southwestern area of the Iberian Peninsula, the negative anomaly reaches 20% of the winter average precipitation. The consistency analysis shows that this precipitation pattern is not the result of a few major events, but rather that it is stable and qualitatively similar to that found during the positive phase of the NAO. A non-linear response to ENSO is found in the eastern Mediterranean area: negative precipitation anomalies are found, having similar amplitude anomalies, both during El Niño and La Niña events. The analysis of the precipitation anomalies for the winter following the selected autumn ENSO events shows very similar results to those found for the previous analysis, thus suggesting the existence of a potential source of seasonal forecasting of European precipitation. An analysis of the sensitivity of the precipitation anomalies to the strength of the ENSO events shows that, when the strength of the ENSO increases, the magnitude of the rainfall anomalies does not change, but the area influenced and the coherence between events do increase slightly. Copyright © 2005 Royal Meteorological Society [source] Variability of the recent climate of eastern AfricaINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 6 2004Carl J. Schreck III Abstract The primary objective of this study is to investigate the recent variability of the eastern African climate. The region of interest is also known as the Greater Horn of Africa (GHA), and comprises the countries of Burundi, Djibouti, Eritrea, Ethiopia, Kenya, Rwanda, Somalia, Sudan, Uganda, and Tanzania. The analysis was based primarily on the construction of empirical orthogonal functions (EOFs) of gauge rainfall data and on CPC Merged Analysis of Precipitation (CMAP) data, derived from a combination of rain-gauge observations and satellite estimates. The investigation is based on the period 1961,2001 for the ,short rains' season of eastern Africa of October through to December. The EOF analysis was supplemented by projection of National Centers for Environmental Prediction wind data onto the rainfall eigenmodes to understand the rainfall,circulation relationships. Furthermore, correlation and composite analyses have been performed with the Climatic Research Unit globally averaged surface-temperature time series to explore the potential relationship between the climate of eastern Africa and global warming. The most dominant mode of variability (EOF1) based on CMAP data over eastern Africa corresponds to El Niño,southern oscillation (ENSO) climate variability. It is associated with above-normal rainfall amounts during the short rains throughout the entire region, except for Sudan. The corresponding anomalous low-level circulation is dominated by easterly inflow from the Indian Ocean, and to a lesser extent the Congo tropical rain forest, into the positive rainfall anomaly region that extends across most of eastern Africa. The easterly inflow into eastern Africa is part of diffluent outflow from the maritime continent during the warm ENSO events. The second eastern African EOF (trend mode) is associated with decadal variability. In distinct contrast from the ENSO mode pattern, the trend mode is characterized by positive rainfall anomalies over the northern sector of eastern Africa and opposite conditions over the southern sector. This rainfall trend mode eluded detection in previous studies that did not include recent decades of data, because the signal was still relatively weak. The wind projection onto this mode indicates that the primary flow that feeds the positive anomaly region over the northern part of eastern Africa emanates primarily from the rainfall-deficient southern region of eastern Africa and Sudan. Although we do not assign attribution of the trend mode to global warming (in part because of the relatively short period of analysis), the evidence, based on our results and previous studies, strongly suggests a potential connection. Copyright © 2004 Royal Meteorological Society. [source] Decadal changes in the link between El Niño and springtime North Atlantic oscillation and European,North African rainfallINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 11 2003Peter Knippertz Abstract The link between El Niño,southern oscillation (ENSO) variability in boreal winter (represented by the NIÑO3 index, i.e. East Pacific sea-surface temperature anomalies) and the large-scale circulation and weather conditions over Europe,northwest Africa in spring is explored, considering station reports of precipitation, sea-level pressure (SLP) anomalies and two North Atlantic oscillation (NAO) indices. It is found that these relations have undergone consistent and simultaneous changes in the 20th century. Three characteristic periods can be identified. During 1900,25 and 1962,87, positive NIÑO3 index values are associated with enhanced precipitation over central Europe and reduced rainfall in southern Europe and northern Africa. The ENSO influence on precipitation over Scotland and Norway is small. The rainfall anomalies can be explained from the advective and dynamical implications of a north,south dipole in SLP correlations (warm ENSO events followed by low pressure in northern Europe and high pressure over the Mediterranean Sea,North Africa). This dipole hardly projects on the commonly used NAO centres (Iceland and Azores/Gibraltar) and thus ENSO,NAO correlations are insignificant. During 1931,56 the NIÑO3 index reveals little influence on precipitation over the Iberian Peninsula and Morocco, but there are large negative correlations with precipitation over Scotland and Norway. This is related to an alteration of the NIÑO3,SLP correlation pattern, which implies high pressure over northern Europe and low pressure over central Europe after warm events, and thus a virtually inverted dipole with respect to the other two periods. The large westward extension of the dipole leads to a significant NAO,NIÑO3 correlation of r = ,0.5. These alterations were accompanied by substantial large-scale circulation changes during the period 1931,56, as revealed by anomalously high pressure and dry conditions over central,western Europe, a change in precipitation-producing SLP patterns for Morocco and an anomalously low number of positive NAO and NIÑO3 index values. It is left for discussion as to whether the decadal variations described are due to a change in the physics of the teleconnection or to stochastic fluctuations. Copyright © 2003 Royal Meteorological Society [source] Seasonal modulation of the El Niño,southern oscillation relationship with sea level pressure anomalies over the North Atlantic in October,March 1873,1996INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 2 2003V. Moron Abstract The seasonal modulation of the relationship between the sea-level pressure anomalies (SLPAs) over the North Atlantic region (100°W,50°E; 20,70°N) and the sea surface temperature anomalies (SSTAs) in the tropical Pacific (120,290°E; 20°N,20°S) is investigated in the northern winter (October to March) from 1873 to 1996, using singular-value decomposition and composite analyses. Both methods show that the pattern of the North Atlantic SLPA associated with the tropical Pacific SSTA in November,December is different from that found in January,March. The surface covered by a significant SLPA is larger in November,December and February,March than in January. In November,December, the warm El Niño,southern oscillation (ENSO) events are associated with negative SLPAs extending from the Hudson Bay to Scandinavia and positive SLPAs over the Azores high. The cold ENSO events are associated with a positive SLPA between Greenland and western Europe. In January, and mainly in February,March, the warm ENSO events are associated with a positive SLPA north of 50°N and a negative SLPA extending from the southeastern USA toward western and central Europe. The cold ENSO events exhibit almost reversed SLPA patterns. The change between November,December and January,March is also observed at the hemispheric scale. In November,December, the SLPAs associated with the warm minus cold ENSO composite form a hemispheric north,south dipole pattern with positive (negative) anomalies south (north) of 40,45°N. In January,March, the SLPA pattern associated with the warm minus cold ENSO composite is close to the tropical Northern-Hemisphere pattern. Copyright © 2003 Royal Meteorological Society. [source] Integrating climate forecasts and natural gas supply information into a natural gas purchasing decisionMETEOROLOGICAL APPLICATIONS, Issue 3 2000David Changnon This paper illustrates a key lesson related to most uses of long-range climate forecast information, namely that effective weather-related decision-making requires understanding and integration of weather information with other, often complex factors. Northern Illinois University's heating plant manager and staff meteorologist, along with a group of meteorology students, worked together to assess different types of available information that could be used in an autumn natural gas purchasing decision. Weather information assessed included the impact of ENSO events on winters in northern Illinois and the Climate Prediction Center's (CPC) long-range climate outlooks. Non-weather factors, such as the cost and available supplies of natural gas prior to the heating season, contribute to the complexity of the natural gas purchase decision. A decision tree was developed and it incorporated three parts: (a) natural gas supply levels, (b) the CPC long-lead climate outlooks for the region, and (c) an ENSO model developed for DeKalb. The results were used to decide in autumn whether to lock in a price or ride the market each winter. The decision tree was tested for the period 1995,99, and returned a cost-effective decision in three of the four winters. Copyright © 2000 Royal Meteorological Society [source] Satellite radar observation of tropical peat swamp forest as a tool for hydrological modelling and environmental protectionAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 3 2007Dirk H. Hoekman Abstract 1.Tropical peat swamp forests may contain as much as 20% of the global soil carbon stock. They are threatened by large-scale deforestation and canal drainage. Oxidation and forest fire cause enormous carbon emissions. Most remaining areas are located in Indonesia. These are becoming increasingly important for maintaining biodiversity. 2.Time series of historical JERS-1 SAR data reveal the extent and nature of recent disturbances, such as those caused by excess drainage and severe ENSO events. Examples are given for a number of peat swamp forest areas in Sumatra and Borneo. 3.Peat swamp hydrology is studied along a 23-km transect, which crosses a complete peat dome. First results show the relevance of surface runoff and peat soil roughness in the description of flooding events, and have been used to produce an improved hydrological description. 4.Since the dynamics of flooding events can potentially be observed by the ALOS PALSAR instrument (yet to be launched), this new hydrological model can be used to infer parameters relevant for detection of ecosystem disturbance and evaluation of restoration efforts. Copyright © 2007 John Wiley & Sons, Ltd. [source] Qualitative modelling for the development of a sustainable management strategy for the Peruvian scallop Argopecten purpuratus (Lamarck 1819)AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 3 2002Marco Ortiz Abstract 1.This study is the first attempt using Levins's Theory (loop analysis) in order to develop a sustainable management for the scallop, Argopecten purpuratus, fishery in Peru during El Niño-Southern Oscillation events (ENSO) and upwelling conditions. Based on this theoretical framework, it was possible to estimate the local stability for each of these model systems and to follow the qualitative changes of the variables in response to external factors. 2.Based on our results, we suggest the following management policies to be implemented: (1) during ENSO events the size at the first capture of the scallops should be >70 mm and (2) the increase in the number of fishermen during ENSO events must be prevented. Both measures increase the sustainability of fishery under ENSO and upwelling conditions. The ecological models predict that during ENSO and upwelling events, any management strategy to increase the recruitment of the scallop would not have a positive impact on the adult stock. 3.Finally, we suggest that more efforts must be focused on the development of extended eco-social models, which incorporate further social and economic variables, increasing realism of the abstractions for this fishery activity. Copyright © 2002 John Wiley & Sons, Ltd. [source] Retracted: ENSO-related modulation of coastal upwelling along the central east coast of IndiaATMOSPHERIC SCIENCE LETTERS, Issue 1 2009K. Muni Krishna Abstract An index of El Niño Southern Oscillation (ENSO) in the Pacific during February through April is shown to account for a significant part of the variability of coastal sea surface temperature (SST) anomalies measured a few months later within the central east coast of India (CEI). This ENSO-related modulation of coastal upwelling appears to contribute to the connection observed at the basin-scale between ENSO and SST in the Bay of Bengal. The ability to use this teleconnection to give warning of large changes in the CEI a few months in advance is exemplified using data 1998,1999 ENSO events. Copyright © 2008 Royal Meteorological Society [source] | ||||||||||||||||