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1.
Meteorological impacts of El Niño events of 1982–1983 and 1997–1998 were observed in locations throughout the world. In southern Brazil, El Niño events are associated with increased rainfall and higher freshwater discharge into Patos Lagoon, a large coastal lagoon that empties into the Atlantic Ocean. Based on interdecadal meteorological and biological data sets encompassing the two strongest El Niño events of the last 50 yr, we evaluated the hypothesis that El Niño-induced hydrological changes are a major driving force controlling the interannual variation in the structure and dynamics of fishes in the Patos Lagoon estuary. High rainfall in the drainage basin of the lagoon coincided with low salinity in the estuarine area during both El Niño episodes. Total rainfall in the drainage basin was higher (767 versus 711 mm) and near-zero salinity conditions in the estuarine area lasted about 3 mo longer during the 1997–1998 El Niño event compared with the 1982–1983 event. Hydrological changes triggered by both El Niño events had similar relationships to fish species composition and diversity patterns, but the 1997–1998 event appeared to have stronger effects on the species assemblage. Although shifts in species composition were qualitatively similar during the two El Niño events, distance between El Niño and non-El Niño assemblage multivariate centroids was greater during the 1996–2000 sampling period compared with the 1979–1983 period. We provide a conceptual model of the principal mechanisms and processes connecting the atmospheric-oceanographic interactions triggered by the El Niño phenomena and their effect on the estuarine fish assemblage.  相似文献   

2.
Recent work on the beach ridges at Santa, Peru (9° s latitude) upholds an earlier hypothesis, based on sedimentary evidence, that the ridges were formed by massive sediment pulses during rains associated with major incursions of the warm water El Niño countercurrent. The ridges can therefore be used to date major El Niño events. The alternate hypothesis for the Santa ridge origin cited minor sequential uplift as the causal factor; this hypothesis has been disproven, though one previously unreported uplift event at about 4200 years B.P. has been identified at Santa. In general, landscape alteration processes such as El Niño floods and tectonic uplift affect human populations, and accurate chronologies of these events are necessary to interpret the archaeological record. Geoarchaeological research offers the key to constructing landscape alteration chronologies, which are also of use to geologists for studies of earthquake prediction, sedimentation processes, and paleoclimatology.  相似文献   

3.
The oceanographic phenomenon known as El Niño is the subject of intensive recent study. Any hypotheses regarding physical causes and predictability of El Niño should consider its geological history. New geoarchaeological evidence suggests that the El Niño phenomenon did not exist along the northern and central coasts of Peru before about 5000 years B.P. Molluscan faunas from archaeological sites at Pampa las Salinas and Salinas de Chao permit temporal bracketing of a major structural change in the East Pacific water mass. The boundary between the warm Panamic Province and the cold Peruvian Province, which today occurs at about 5 degrees south latitude, was some 500 km further south from at least 11,000 years B.P. to about 5000 years B.P. This conclusion is corroborated by many other lines of evidence including phosphorite distribution, timing of glacial retreat, sea level change, radiolarian, diatom and fish scale distributions, and beach ridge patterns. The present day arid coastal climate of north central Peru is probably a post-5000 year B.P. development. Hunter–gatherer populations of the area would most likely have exploited more land-based seasonal resources from grasslands and forests before 5000 years B.P., and relied less upon the diminished productivity of warm water maritime resources.  相似文献   

4.
The northern segment of the Peruvian Andes is affected by a twofold climate with measurable implications on landscapes and landscape dynamics. During ‘normal’ or ‘neutral’ years easterly winds bring rain from the Atlantic and the Amazon Basin to the Sierras, which results in a seasonal climate with rather low-intensity precipitations. In contrast, during the large-scale warm phase of the ENSO cycle, El Niños transfer moisture from the Pacific to the Peruvian coast by westerly winds and result in high-intensity precipitation. We investigate the effects of this twofold climate for the case of the Piura drainage basin at ca. 5°S latitude (northern Peru). In the headwaters that have been under the influence of the easterlies, the landscape is mantled by a thick regolith cover and dissected by a network of debris flow channels that are mostly covered by a thick layer of unconsolidated sediment. This implies that in the headwaters of the Piura River sediment discharge has been limited by the transport capacity of the sediment transfer system. In the lower segment that has been affected by high-intensity rainfall in relation to the westerlies (El Niños), the hillslopes are dissected by debris flow channels that expose the bedrock on the channel floor, implying a supply-limited sediment discharge. Interestingly, measurements at the Piura gauging station near the coast reveal that, during the last decades, sediment was transferred to the lower reaches only in response to the 1982–1983 and 1997–1998 El Niño periods. For the latter period, synthetic aperture radar (SAR) intensity images show that the locations of substantial erosion are mainly located in areas that were affected by higher-than-average precipitation rates. Most important, these locations are coupled with the network of debris flow channels. This implies that the seasonal easterlies are responsible for the production of sediment through weathering in the headwaters, and the highly episodic El Niños result in export of sediment through channelized sediment transport down to the coastal segment. Both systems overlap showing a partially coupled sediment production–delivery system.  相似文献   

5.
Spartina alterniflora and Spartina densiflora are native salt marsh plants from the Atlantic coast; their habitats in Patos Lagoon estuary (southern Brazil) are characterized by a microtidal regime (<0.5 m) and, during El Niño events, high estuarine water levels and prolonged flooding due to elevated freshwater discharge from a 200,000-km2 watershed. During and between El Niño events, the vegetative propagation of these two Spartina species in the largest estuary of southern Brazil (Patos Lagoon) was evaluated by monitoring transplanted plants for 10 years (short-term study) and interpreting aerial photos of natural stands for 56 years (long-term study). During the short-term study, S. alterniflora quickly occupied mud flats (up to 208 cm year?1) by elongation of rhizomes, whereas S. densiflora showed a modest lateral spread (up to 13 cm year?1) and generated dense circular-shaped stands. However, moderate and strong El Niño events can promote excessive flooding and positive anomalies in the estuarine water level that reduce the lateral spread and competitive ability of S. densiflora. During the long-term study, natural stands of S. alterniflora and S. densiflora had steady lateral spread rates of 152 and 5.2 cm year?1, respectively, over mud flats. In the microtidal marshes of the southwest Atlantic, the continuous long-term lateral expansion of both Spartina species embodies periods of intense flooding stress (moderate and strong El Niños), when there is a decrease of vegetative propagation and less stressful low water periods of fast spread over mud flats (non-El Niño periods and weak intensity El Niños).  相似文献   

6.
The importance of the El Niño-Southern Oscillation (ENSO) on regional-scale climate variability is well recognized although the associated effects on local weather patterns are poorly understood. Little work has addressed the ancillary impacts of climate variability at the community level, which require analysis at a local scale. In coastal communities water quality and public health effects are of particular interest. Here we describe the historical influence of ENSO events on coastal water quality in Tampa Bay, Florida (USA) as a test case. Using approximate randomized statistics, we show significant ENSO influences on water quality particularly during winter months, with significantly greater fecal pollution levels during strong El Niño winters and significantly lower levels during strong La Niña winters as compared to neutral conditions. Similar significant patterns were also noted for El Niño and La Niña fall periods. The success of the analysis demonstrates the feasibility of assessing local effects associated with large-scale climate variability. It also highlights the possibility of using ENSO forecasts to predict periods of poor coastal water quality in urban region which local agencies may use to make appropriate prepations.  相似文献   

7.
Chemical proxies are useful analogs for reconstructing physical properties of sea water, such as sea surface temperature (SST) and sea surface salinity (SSS). Time series of these inferred properties would allow for reconstructions of past El Niño–Southern Oscillation (ENSO) events, where no instrumental records exist. In this study, a monthly oxygen isotope record from a Porites coral is used to explain how past ENSO events are recorded in the coral skeletons. The sample covers a 12 year period and was collected from Nanwan Bay, Taiwan. During El Niño events the coral skeleton is shown to produce a δ18O–SST correlation with a slope of −0.12 ± 0.04‰ °C−1. During other times, this value is significantly different, with a slope of −0.21 ± 0.04‰ °C−1. Coral that grew during El Niño summers have δ18O values which are enriched by ∼0.2‰, relative to other times. A possible mechanism to explain this difference may be enhanced penetration of Kuroshio Current waters into the South China Sea during summer. The observed contrast in the correlation of δ18O–SST variability in this sample supports the influence of El Niño in eastern Asia.  相似文献   

8.
The objective of research done in this study is to examine the variability of the length of day (LOD) and to investigate its correlation with ENSO (El Niño-Southern oscillation) episodes. For this purpose, the LOD time series (1962–2015), from the International Earth Rotation and Reference Systems Service (IERS), is investigated using the Singular Spectrum Analysis (SSA) technique. The results show that the LOD time series is very complex and is composed of several components: the long-term trend explains 95.97% of the original series, the annual harmonic 1.76% and the semi-annual 1.35%. Considering sea surface temperature anomalies (SSTA) index over the Niño3, Niño4 and Niño3.4 regions, Southern Oscillation Index (SOI) and Multivariate ENSO Index (MEI), the residuals signal, that represents only 0.92% of the initial LOD series, indicate a significant correlation with ENSO occurred during 1965–66, 1972–73, 1982–83 and 1997–98 El Niño events and 1970–71, 1973–74, 1988–89, 2007–08, 2010–11 La Niña ones. This is a pertinent result that suggests that LOD variability is at least partly related to ENSO phenomena.  相似文献   

9.
This study evaluates impacts from tropical cyclone (TC) landfalls on populated areas located along the Pacific Ocean coast of Mexico. The period of interest is from 1970 through 2010 and an international disaster database is used to identify the impact from the landfalling TCs. More than 30 landfall events occurred during the period; we examined the top 25 TCs based on rainfall accumulation, as well as the top 10 TC-related disasters based on the affected population. Each event resulted in affected population from 20 000 to more than 800 000. Strong winds and heavy rainfall, during periods of one to three days, are associated with property damage and loss of lives. Our results indicate that excessive rainfall accumulations and daily rates, over highly populated areas, are important elements associated with the occurrence of disasters. Six of the top 10 TC-related disasters occurred during El Niño and three during neutral conditions; however, looking at the top 25 events, 10 occurred during El Niño and 10 during neutral conditions. Three case studies that occurred during El Niño events (Liza in 1976, Pauline in 1997, and Lane in 2006) are documented in more detail as they affected areas with different population densities in the southern and northwestern coasts of Mexico.  相似文献   

10.
Estuarine salinity distributions reflect a dynamic balance between the processes that control estuarine circulation. At seasonal and longer time scales, freshwater inputs into estuaries represent the primary control on salinity distribution and estuarine circulation. El Niño-Southern Oscillation (ENSO) conditions influence seasonal rainfall and stream discharge patterns in the Tampa Bay, Florida region. The resulting variability in freshwater input to Tampa Bay influences its seasonal salinity distribution. During El Niño events, ENSO sea surface temperature anomalies (SSTAs) are significantly and inversely correlated with salinity in the bay during winter and spring. These patterns reflect the elevated rainfall over the drainage basin and the resulting elevated stream discharge and runoff, which depress salinity levels. Spatially, the correlations are strongest at the head of the bay, especially in bay sections with long residence times. During La Niña conditions, significant inverse correlations between ENSO SSTAs and salinity occur during spring. Dry conditions and depressed stream discharge characterize La Niña winters and springs, and the higher salinity levels during La Niña springs reflect the lower freshwater input levels.  相似文献   

11.
Thunderstorms are of much importance in tropics, as this region is considered to have central role in the convective overturn of the atmosphere and play an important role in rainfall activity. It is well known that El Niño and La Niña are well associated with significant climate anomalies at many places around the globe. Therefore, an attempt is made in this study to analyze variability in thunderstorm days and rainfall activity over Indian region and its association with El Niño and La Niña using data of thunderstorm day’s for 64 stations well distributed all over India for the period 1981–2005 (25 years). It is seen that thunderstorm activity is higher and much variable during pre-monsoon (MAM) and southwest monsoon (JJAS) than the rest of the year. Positive correlation coefficients (CCs) are seen between thunderstorms and rainfall except for the month of June during which the onset of the southwest monsoon sets over the country. CCs during winter months are highly correlated. Composite anomalies in thunderstorms during El Niño and La Niña years suggest that ENSO conditions altered the patterns of thunderstorm activity over the country. Positive anomalies are seen during pre-monsoon (MAM) and southwest monsoon months (JAS) during La Niña years. Opposite features are seen in southwest monsoon during El Niño periods, but El Niño favors thunderstorm activity during pre-monsoon months. There is a clear contrast between the role of ENSO during southwest monsoon and post-monsoon on thunderstorm activity over the country. Time series of thunderstorms and precipitation show strong association with similarities in their year-to-year variation over the country.  相似文献   

12.
Trends of pre-monsoon, monsoon and post-monsoon rainfall pattern were studied on decadal basis over different homogeneous monsoon regions in India for the period 1871–2008. It is attempted to understand the relation of monsoon rainfall with the global teleconnections of El Niño and La Niña, for which the correlation analysis has been carried out with Darwin pressure and Niño 3.4 sea surface temperature (Niño 3.4 SST). The correlation analysis inferred that the significant correlations were observed when monsoon rainfall is related to ENSO indices on decadal scale than on annual ones. The study also found that the north-west region is more affected by the moderate El Niño years compared to strong El Niño years. The regions Central North-East and North-East could not make any difference among weak, moderate and strong La Niña events. The authors also have carried out the extreme value analysis over different homogeneous monsoon regions of India as well as for whole India. The results show that the return values of rainfall are increasing with the return periods for the forthcoming 10, 20, 50 and 100 years. The heterogeneity in number of threshold years that were recorded for the extreme rainfall over north-east (humid climatic type) and north-west (arid climatic type) described the climate variability. The results of the present study may be useful for the policy makers in understanding the rainfall exceedance in different return periods for planning the risk management strategies.  相似文献   

13.
We present the results of sclerochronologically calibrated growth and stable isotope analyses of the freshwater bivalve Margaritifera falcata collected from an agricultural, suburban setting near Vancouver, BC. The oxygen isotope range of shell aragonite can be explained by the temperature range during the growing season, assuming the water δ 18O composition remained constant. However, shell growth is strongly influenced by local summer precipitation and potentially runoff of nutrient-rich stormwater. About 44% of the variability of annual shell growth can be explained by amounts of local summer (June–September) rainfall. Local winter precipitation and El Niño–Southern Oscillation (ENSO) strength during the preceding year exert a weak, but significant control on shell growth. In combination, summer and winter precipitation can explain up to 50% of the variability in annual shell growth. Spectral analyses substantiate the effect of precipitation on shell growth and demonstrate that shell growth and ENSO are coupled by precipitation. Common spectral density was found at periods of 6.5–9 years, particularly between 1985 and 2004. Higher frequency oscillation corresponding to periods of 3–5 years occurred during the early 1970s, early to mid 1980s, and later 1990s. These results suggest that skeletal records of bivalve mollusks provide suitable archives of ENSO-coupled precipitation in areas where other climate proxies such as tree-rings and speleothems may not be available.  相似文献   

14.
The study analyzes drought using Standardized Precipitation Index (SPI) and Mann-Kendall (MK) Trend Test in the context of the impacts of drought on groundwater table (GWT) during the period 1971-2011 in the Barind area, Bangladesh. The area experienced twelve moderate to extreme agricultural droughts in the years 1972, 1975, 1979, 1982, 1986, 1989, 1992, 1994, 2003, 2005, 2009 and 2010. Some of them coincide with El Niño events. Hydrological drought also occurred almost in the same years. However, relationship between all drought events and El Niño is not clear. Southern and central parts of the area frequently suffer from hydrological drought, northern part is affected by agricultural drought. Trends in SPI values indicate that the area has an insignificant trend towards drought, and numbers of mild and moderate drought are increasing. GWT depth shows strong correlation with rainy season SPI values such that GWT regaining corresponds with rising SPI values and vice versa. However, 2000 onwards, GWT depth is continuously increasing even with positive SPI values. This is due to over-exploitation of groundwater and changes in cropping patterns. Agricultural practice in Barind area based on groundwater irrigation is vulnerable to drought. Hence, adaptation measures to minimize effects of drought on groundwater ought to be taken.  相似文献   

15.
Since Holocene time, above-mean precipitations recorded during the El Niño warm ENSO phase have been linked to the occurrence of severe debris flows in the arid Central Andes. The 2015–2016 El Niño, for its unusual strength, began driving huge and dangerous landslides in the Central Andes (32°) in the recent South Hemisphere summer. The resulting damages negatively impacted the regional economy. Despite this, causes of these dangerous events were ambiguously reported. For this reason, a multidisciplinary study was carried out in the Mendoza River valley. Firstly, a geomorphological analysis of affected basins was conducted, estimating morphometric parameters of recorded events such as velocity, stream flow, and volume. Atmospheric conditions during such events were analyzed, considering precipitations, snow cover, temperature range, and the elevation of the zero isotherm. Based on our findings, the role of El Niño on the slope instability in the Central Andes is more complex in the climate change scenario. Even though some events were effectively triggered by intense summer rainstorm following expectations, the most dangerous events were caused by the progressive uplifting of the zero isotherm in smaller basins where headwaters are occupied by debris rock glaciers. Our research findings give light to the dynamic coupled system ENSO–climate change–landslides (ECCL) at least in this particular case study of the Mendoza River valley. Landslide activity in this Andean region is driven by wetter conditions linked to the ENSO warm phase, but also to progressive warming since the twentieth century in the region. This fact emphasizes the future impact of the natural hazards on Andean mountain communities.  相似文献   

16.
东亚冬季冷暖变化与El Ni?o事件   总被引：1，自引：0，他引：1       下载免费PDF全文
近十年来,东亚冬季气温明显升高。本文分析证明,东亚温度变化与赤道东太平洋和北太平洋重要洋流区的海表面温度(SST)有密切的遥相关。如果赤道东太平洋SST异常偏高(或异常偏低),即出现埃尔尼诺(或反埃尔尼诺)事件,则在其后7～24个月中,我国华北和东北将出现暖冬(或冷冬),渤海冰情将出现轻冰年(或重冰年)。据此建立的回归预报方程,对1988/1989年和1989/1990年冬季渤海海冰的预报结果完全正确。  相似文献   

17.
To reconstruct the palaeoproductivity evolution history of the centre of the western Pacific warm pool (WPWP) over the last 250 ka, multi‐proxies were analysed in sediment core WP7 recovered from the Ontong–Java Plateau. Palaeoproductivity evolution at the centre of the WPWP during the last 250 ka is closely related to glacial–interglacial cycles and the insolation controlled by precession. The glacial higher primary productivity relative to the interglacial conditions could have resulted from both thermocline shoaling associated with persistent El Niňo‐like conditions and the increased influx of dust resulting from intensified winter monsoon together with important changes in the thermocline. The minimum primary productivity values during the last three terminations could be resulted from deglacial thermocline deepening and intensified stratification associated with persistent La Niña‐like conditions, and the concurrent Neogloboquadrina dutertrei δ13C minimum events probably reflect the chemical signatures of Subantarctic Mode Water and Antarctic Intermediate Water. In addition, primary productivity values are also controlled by the thermocline variations resulting from El Niño/La Niña‐Southern Oscillation processes responding to precession forcing, and lead the δ18O by about 4 ka. The 33.1 ka, 19 ka and “half‐precession” periods are prominent in the palaeoproductivity records. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

18.
《Atmósfera》2014,27(2):103-115
This study examined precipitation in southern Brazil based on a data set provided by the Brazilian National Water Agency, covering the period from 1976 to 2010. Data were homogenized using the R software and the Climatol subroutine, which allow completing missing data. Isohyets were drawn using the Geostatistics software to obtain a semivariogram for each analysis. There was a remarkable interannual variability in this region, with positive anomalies in the warm phase (El Niño) and negative anomalies in the cold phase (La Niña) of ENSO. Also, the responses of this variability were not uniform in the entire region, since there was variability from year to year and from event to event.  相似文献   

19.
On the basis of model calculations, mutually fitted fields were obtained for the key hydrophysical properties in the vicinity of the hydrological sections executed in the Barents Sea during 1997–1998. Integrated analysis of these data allowed us to evaluate the variability of crucial hydrodynamic conditions: the decrease of supply of relatively warm and saline North Atlantic waters with compensatory inflow of Arctic waters; the decrease of total heat content and increase of thermal convection; the weakening of water dynamics in the system of general cyclone circulation; and the abnormally cold winter in 1997–1998 with the increase in the ice covering of the Barents Sea. With a high confidence probability, it was found that considerable deviations from the mean weather conditions took place in response to the El Niño global disturbance of the same period, with the maximum southern oscillation index (SOI) in January–March 1998. The El Niño signal in the baric field of the Arctic basin, noted even in November–December 1997 as a crest of increased pressure, reached its maximum development in April–June 1998 in the form of a well-pronounced atmospheric anticyclone. Recognizing the natural correlation of this phenomenon and the maximum SOI value, one may state that the Barents Sea responds to an El Niño event in about three months. This circumstance should be used as an important parameter for climate forecasting.  相似文献   

20.

Traditional undergraduate education in earth sciences does not emphasize data acquisition, analysis, or assessment. However, arrival of the information age dictates that earth sciences graduates be imbued with fundamental skills to organize, evaluate and process large data sets. Fortunately, the proliferation of remotely sensed data and its availability via the Internet provides many opportunities for earth science educators to meet these needs. Exercises to introduce students to data analysis have been designed utilizing data from the Tropical Atmosphere–Ocean (TAO) Array and the 1997–1998 El Niño episode in the tropical Pacific Ocean. The TAO Array is a grid of 69 buoys moored across the equatorial Pacific Ocean (8°N to 8°S and 95°W to 143°E) recording environmental data relevant to El Niño—Southern Oscillation (ENSO) processes. Data from the TAO Array is available in near-real-time (http://www.pmel.noaa.gov/toga-tao/realtime.html) or as archived ASCII files (http://www.pmel.noaa.gov/toga-tao/data-delivery.html) providing daily (sometimes hourly) records of environmental parameters for each buoy in the grid. Student exercises in data analysis begin with downloading data from buoy locations, parsing the data into spreadsheets, and organizing data by environmental parameter into yearly and monthly data sets. Analyses of reconstructed data include calculations of long-term averages of environmental parameters, seasonal climatologies, monthly climatologies and calculation of long-term, seasonal, and monthly anomalies. Finally, monthly anomaly maps produced by students are loaded sequentially into GIF-animation software to create time-series images illustrating the progress and development of the 1997–1998 El Niño event.

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