El Nino Occurrences Research Articles

Investigation of the Indian summer in the state's popular capital and correlation between IMD and ERA5 dataset during the past five decades (1973–2022)

In this comprehensive study, spanning five decades from 1973 to 2022, the increasing prevalence and duration of heat waves in India, particularly in central and northwest regions, are examined. These heat waves are found to be associated with elevated pressures, anticyclonic flow patterns, clear skies, and diminishing soil moisture. Furthermore, variations in sea surface temperatures (SST) in the tropical Indian Ocean and the central Pacific significantly influence the occurrence of heat waves in India. The study predicts longer and more frequent heat waves as a consequence of the warming tropical Indian Ocean and an increase in El Nino occ-urrences, highlighting the growing heat-related challenges facing the country. Analyses of the present climate using climate models agree with the highest temperature zones that have been observed, emphasizing the importance of radiative heating. This study determines the areas that are most vulnerable to heat waves and regions with the highest temperatures, and it pinpoints the cause as wind flow from these areas, which is induced by favourable atmospheric circulations. The findings of this investigation would have broad applications in both vulnerability and risk evaluation as well as prediction. This study focused on the ERA-Interim and IMD gri-dded data sets in order to evaluate the validity of heatwave detection across several datasets. It looked at particular heatwave dates from March to June in several places and years, included Lucknow in 2016, Delhi in 2019, Jaipur in 2016, and Bhubaneswar in 1988. Among the two datasets, the research showed a statistically substantial agreement, especially during Lucknow's 2016 summer heatwave. However, Bhubaneswar had the lowest correlation, suggesting that the temperature profile in both datasets was identical. With a larger concentration of matched pixels at the mean temperature, Jaipur in 2019 had the best fit. The study's findings were summarized by pointing out the significance of the mid-temperature range from 30°C to 40°C in heatwave identification.

Satellite Oceanographic Data Processing and Analysis: Correlation Between Nino 3.4 Sea Surface Temperature & Sea Surface High and Wind

El Nino Southern Oscillation (ENSO) is an irregular climate oscillation induced by sea surface temperature anomalies (SSTA) in the Equatorial Pacific Ocean. An anomalous warming in this area is known as El Nino, while an anomalous cooling bears the name of La Nina. The objectives of this study are to: reproduce Oceanic Nino Index (ONI) based on MW OISST; produce Nino Region 3.4 wind and Sea Surface High (SSH); analyze the correlation between SST and Wind & SSH; discuss Typhoon Soudelor based on SST, Wind, and SSH; and analyze the correlation of El Nino and Precipitation in specific area. MWOI-SST was used to produce monthly mean SST over Nino 3.4 region from January 1998 – May 2020. Monthly wind data was obtained from QuickScat. Daily Sea Surface High (SSH) was obtained from Copernicus Marine Environment Monitoring Service (CMEMS). Daily precipitation from TRMM 3B42 over Bandung City (Indonesia) was used to assess the correlation between El Nino and precipitation in specific area. The results show that in Nino 3.4 region, 2015 is the hottest year during 1998-2020 period with average SST of 28.5oC, and 1999 is the coldest year with average SST of 25.7oC. The result shows that the MWOI-SST Ocean Nino Index has very strong correlation with ERSST.v5 with coefficient of correlation is 0.92 and RMSE is 0.36oC. the wind speed of Nino 3.4 region is range from 5.23 m/s to 7.97 m/s. Unlike Sea Surface Temperature (SST), annual average wind speed is more stable with monthly variation. The wind speed is observed high in the beginning and the end of years. Sea Surface Height (SSH) over Nino 3.4 region varied from 65.8 cm to 106.8 cm. 2015 is the highest SSH with annual average of 96 cm, whereas 1999 is the lowest SSH with annual average of 71.4 cm. It is observed that Sea Surface Temperature (SST) has negative correlation with wind speed with coefficient of correlation of 0.28. Conversely, Sea Surface Temperature (SST) over Nino 3.4 region has positive correlation with Sea Surface High (SSH) with coefficient of correlation of 0.30. which mean the higher temperature, the higher Sea Surface Height. During the passage of Typhoon Soudelor, there is evident cool trail along its track with rightward bias. We can assume that the decreasing precipitation in Bandung City might be affected by strong El Nino occurrence in 2015.

Dynamics of basal area increment and carbon value of natural forest stands in response to the El Nino occurrence in East Kalimantan

Climate change will have an impact on ecosystems, both flora and fauna. Forest stands or vegetation will have different resilience. This is indicated by a varied growth response. This study aims to show the dynamics of vegetation increment and carbon value of natural forest stands in response to the occurrence of El Nino. The research was conducted on permanent sample plots of primary mixed Dipterocarps forest in Labanan, East Kalimantan, which was built as many as 12 plots (12 ha) which were monitored along for 30 years (measurement period 1990-2020). The approach to assessing the vegetation response is based on the parameters of the basal area increment level and the carbon value of stands which are divided into aboveground and total. The analysis of the dynamics of the response is arranged in terms of time, with the existence of long post-el Nino drought conditions that occurred in 1997/1998 and 2015 in East Kalimantan. Variations in growth dynamics will occur in species groups based on ecophysiology factors. Assessment of primary forest provides an overview of growth rates based on genetic characteristics of the vegetation composition. The existence of El Nino as a factor in this condition is possible to decrease the density and basal area increment of stand after fourth year. The El Nino effect will reduce the total carbon value of primary forest stands by around 7.7-20.3% from the initial reserve.

AN EVALUATION ON OUTCOME OF OIL PALM REPLANTING SCHEME (TSSPK) AND NEW PLANTING SCHEME (TBSPK)

The Oil Palm Assistance Scheme for Replanting (TSSPK) and the New Planting (TBSPK) for Independent Smallholders (ISH) were inaugurated in 2011 as part of the 10th Malaysia Plan. It is a subset of the National Key Economic Area (NKEA) Oil Palm Commodities Entry Point Project 1 (EPP1). Among the assistance included in these schemes are the high-quality seedlings, agricultural inputs such as fertilisers and pesticides along with the cash fund for land preparation and cultivation of the seedlings. The smallholders who participated in these schemes were also given extension services by the MPOB extension agent (TUNAS) on various aspects of oil palm management. A total of 382 participants were involved and responded to the survey. The proportion of respondents are from Sabah (38.5%), Sarawak (38%), and Johor (23.6%). The study found that the average age of the participants mostly is 60 years old and above (40.1%), and 57.4% of participants were the owner of the oil palm plantation. The range of fresh fruit bunch (FFB) production harvested for the first and second year is between 0 - 4.6t/ha/year, which is slightly low due to the El Nino occurrence in 2016. A profit in income was recorded from the FFB sales after participating in the scheme. The low-income category recorded a decrease of 30.11% while the higher income category showed an increased between 2.66% to 16.59% after they joined the schemes. Some participants also implemented the integrated cash crops alongside the oil palm to generate income while waiting for the immature oil palm to produce yield. This study shows that most of the respondents complied with the Good Agriculture Practice (GAP) after joining the scheme. Most of the participants were pleased with the implementation of the schemes and services done by the TUNAS Officers and gave them an excellent rating. Several improvements are suggested such as agriculture input distribution, clustering the smallholders into cooperatives, continuity of GAP implementation, and comprehensive research in the future.

Inter-annual variability and skill of tropical rainfall and SST in APCC seasonal forecast models

The present study explored the performance of the current coupled models obtained from the Asia Pacific Economic Cooperation (APEC) Climate Centre (APCC) in representing the tropical Indo-Pacific sea surface temperature (SST) and rainfall during boreal summer season (June through September; JJAS). We have used the retrospective/hindcast runs for 28 years from 1983 to 2010 initialized in May. The mean SST bias in the tropical Indo-Pacific Oceans showed large diversity among the models in JJAS. In the case of the rainfall, most of the models displayed a strong dry bias over the major continental regions and wet biases over the tropical oceans. The majority of the models simulated the Inter-annual variability (IAV) of JJAS rainfall and SST reasonably well over the equatorial Pacific region, where the models are close to observed IAV and maximum signal to noise ratio (SNR). It is found that the models display, low IAV of rainfall and SST over the Indian Ocean with low SNR values, resulting in less predictive skill as compared to the tropical Pacific region. Similarly, all models showed a higher skill in summer rainfall prediction over the oceanic regions compared to the Asian land region, where SNR is very low. Further analysis suggested that the models have greater skill in predicting El Nino-Southern Oscillation (ENSO). The category wise analysis showed that models could predict 60–70% of the extreme ENSO events, but the normal events are represented only by 50%. It is noted that the models predict many false alarms for El Nino resulting in a higher frequency of El Nino occurrence. This is mainly responsible for stronger ENSO and the Asian Monsoon teleconnections in the models than in the observations. Meanwhile, the category wise rainfall skill for extended Indian monsoon region (EMR) displayed 50–60% accuracy for the extreme monsoon years and is around 50% for normal years. However, models such as CCSM3, CFSV2, and CANCM3 have displayed higher rainfall skills over EMR as compared to the other models possibly due to better representation of teleconnections spatial patterns between EMR rainfall and SST anomalies over Indo-Pacific Oceans.

ENSO diversity and the recent appearance of Central Pacific ENSO

ENSO diversity refers to the appearance in recent decades of different El Nino types in the tropical Pacific: In addition to the canonical El Nino, the newly discovered type, called Central Pacific (CP) El Nino, has its center of warming shifted more to the central equatorial Pacific. Whether these ENSO types are really distinct or are different manifestations of a continuum is currently under debate. The mechanisms for the recent appearance of the additional type of ENSO have not been clarified. While previously it was claimed that the increased CP El Nino occurrence in recent decades were due to tropical trade winds weakened by global warming, the observed trade winds actually intensified. We systematically study the variability of the Pacific sea-surface temperature (SST) using the new method of Rotated Principal Component Analysis (RPCA). The essential statistical characteristics of these two El Nino types are found to be describable by only three fundamental modes of pan-Pacific SST with different proportions: the ENSO-cycle, the pan-Pacific counterpart of the regionally defined Pacific Decadal Oscillation (PDO), and a new climate mode we call the Central Pacific Variability (CPV). It is shown that CP El Nino can be described by the PDO and the CPV. The latter has a horseshoe-shaped warm SST pattern in the Central Pacific flanked by cold SST to the east, roughly similar to the original definition of ENSO Modoki by Ashok et al. (J Geophys Res Oceans 112:C11007, 2007) as the second Empirical Orthogonal Function in a narrow tropical domain decomposition. The Principal Component (PC) of this mode, called Modoki PC (MPC) was thought to characterize the occurrence of this new phenomenon, but it has been shown to be unable to separate it from the canonical ENSO. In contrast, we demonstrate that Central Pacific El Nino occurs when the CPV index is larger than 0.5. The intensity of the CPV mode has increased dramatically since 1970s, likely as a result of the intensification of the easterly trade winds in the tropical Pacific, which tilts the thermocline along the tropical Pacific and raises the SST in the central equatorial Pacific. Moderate El Ninos are more prone to stalling in the Central Pacific, becoming CP El Ninos.

Weather noise leading to El Niño diversity in an ocean general circulation model

The frequency of Central Pacific (CP) El Nino occurrences has increased since the late 1990s. In spite of a wealth of studies, however, the physical mechanisms that have caused the change remain unclear. We hypothesize that atmospheric weather noise plays a role in these occurrences. To test this hypothesis, we conduct four simulations using Modular Ocean Model version 4 (MOM4) forced by atmospheric weather noise. In this study, the atmospheric weather noise is defined as the random noise obtained from the European Centre for Medium-Range Weather Forecasts atmospheric datasets. In the first experiment, MOM4 is forced by atmospheric weather noise before 1999 along with the corresponding climatological mean state. In the second experiment, MOM4 is forced by atmospheric weather noise after 1999 along with the corresponding climatological mean state. The third and fourth experiments are similar to the first two experiments except the time periods of the climatological mean state are switched. The results show that atmospheric weather noise may play a more important role than the climatological mean state in the increase of CP El Nino occurrences. This implies that the El Nino diversity could be caused by the modulation of atmospheric weather noise. Therefore, it is important to explore how the atmospheric weather noise might change in light of global warming.

Fair Weather or Foul? The Macroeconomic Effects of El Niño

This paper employs a dynamic multi-country framework to analyze the international macroeconomic transmission of El Nino weather shocks. This framework comprises 21 country/region-specific models, estimated over the period 1979Q2 to 2013Q1, and accounts for not only direct exposures of countries to El Nino shocks but also indirect effects through thirdmarkets. We contribute to the climate-macroeconomy literature by exploiting exogenous variation in El Nino weather events over time, and their impact on different regions crosssectionally, to causatively identify the effects of El Nino shocks on growth, inflation, energy and non-fuel commodity prices. The results show that there are considerable heterogeneities in the responses of different countries to El Nino shocks. While Australia, Chile, Indonesia, India, Japan, New Zealand and South Africa face a short-lived fall in economic activity in response to an El Nino shock, for other countries (including the United States and European region), an El Nino occurrence has a growth-enhancing effect. Furthermore, most countries in our sample experience short-run inflationary pressures as both energy and non-fuel commodity prices increase. Given these findings, macroeconomic policy formulation should take into consideration the likelihood and effects of El Nino weather episodes.

Impact of the winter North Atlantic Oscillation (NAO) on the Western Pacific (WP) pattern in the following winter through Arctic sea ice and ENSO: part I—observational evidence

On the basis of a 51-year statistical analysis of reanalysis data, we propose for the first time that the positive phase of the Western Pacific (WP) pattern in the winter is linked to the negative phase of the North Atlantic Oscillation (NAO) in the previous winter, and vice versa. We show that there are two possible mechanisms responsible for this interannual remote linkage. One is an Arctic mechanism. Extensive Arctic sea ice in the summer after a negative NAO acts as a bridge to the positive phase of the WP in the next winter. The other mechanism involves the tropics. An El Nino occurrence after a negative winter NAO acts as another bridge to the positive phase of the WP in the following winter. The timescale of the Arctic route is nearly decadal, whereas that of the tropical route is about 3–5 years. The tropical mechanism indicates that the NAO remotely excites an El Nino in the second half of the following year. A process perhaps responsible for the El Nino occurrence was investigated statistically. A negative NAO in the winter increases Eurasian snow cover. This anomalous snow cover then intensifies the cold air outbreak from Asia to the western tropical Pacific. This outbreak can intensify the westerly wind burst and excite El Nino in the following year. We suggest that the phase of the NAO in the winter could be a predictor of the WP in the following year.

Early detection of drought impact on rice paddies in Indonesia by means of Niño 3.4 index

El Nino events have been frequently marked by drought occurrences with severe consequences for agricultural production in Indonesia. Paddy drought occurs almost every year and extends during El Nino phenomena. The Nino 3.4 index is commonly used as an important tool for managing a food security policy. However, there are no details regarding the impact of El Nino on drought-induced paddy damage. We developed the Paddy Drought Impact Index (PDII), which is the ratio of drought-induced paddy damaged area to the total paddy area planted in order to investigate the impact of drought on paddies among 335 districts in Indonesia. Unlike other agricultural drought indices, this index represents real-life percentage of drought-induced paddy damage to indicate each district’s relative severity to drought, which can be easily understood by practical users. The connection between the Nino 3.4 index and PDII was assessed using cross correlation analysis. Scatter plots of best lag time Nino 3.4 index against PDII were examined. The findings show that with 2 months lag of Nino 3.4 prior to PDII, March and June Nino 3.4 indices can be used to predict May–July and August–October PDII, respectively. Critical thresholds of the March Nino 3.4 index were found to range from 0.0 to 0.5 °C, which is associated with a 0.57 probability of weak El Nino occurrence during the subsequent 5 months. On the other hand, a higher probability of 0.67 for occurrences of moderate El Nino is associated with the critical thresholds of June Nino 3.4 index, which ranges from 0.5–1.0 °C. This study has found that the potential impact of drought due to the weak and moderate El Nino occurrences in Indonesia is such that yields are reduced by about 40 % in average. We also found that the most drought-prone areas are located in West Java for both May–July and August–October and in South Sulawesi for August–October.

Multi-timescale variation of East Asian winter monsoon intensity and its relation with sea surface temperature during last millennium based on ECHO-G simulation

Based on the simulation results derived from ECHO-G global coupled climate model, several East Asian winter monsoon (EAWM) indices are compared in order to choose the most suitable one for signaling the intensity of winter monsoon in the last millennium. The index I_shi, which is defined with normalized sea level pressure difference between sea and land in mid and low latitudes, is selected to describe the winter monsoon intensity variation owing to its better capability for reflecting the variation of winter monsoon subsystems, such as the continental high pressure, Aleutian low, East Asian major trough, westerly jet stream, and surface air temperature than the other indices examined. Wavelet analysis on index I_shi shows that the EAWM intensity is characterized by multi-timescale variation with inter-annual, decadal, inter-decadal and inter-centennial oscillations on the background of a slight descending trend. Correlation analysis between the EAWM index and sea surface temperature (SST) at various timescales reveals that the SST in mid-latitudes might provide the background of the EAWM strength changes above decadal timescales, and a negative-feedback process lasting for about two years is found between the EAWM intensity and the SST in the eastern equatorial Pacific. According to the correlation, the El Nino occurrence in the second-half of the year leads to weaker EAWM than normal in the following winter and the weakened EAWM corresponds to lower SST in eastern equatorial Pacific after about half a year, which will then strengthen the EAWM intensity in the next winter. It is a stable feedback process and its mechanism is discussed.

Vertical structure variability and equatorial waves during central Pacific and eastern Pacific El Niños in a coupled general circulation model

Recent studies report that two types of El Nino events have been observed. One is the cold tongue El Nino or Eastern Pacific El Nino (EP El Nino), which is characterized by relatively large sea surface temperature (SST) anomalies in the eastern Pacific, and the other is the warm pool El Nino (a.k.a. ‘Central Pacific El Nino’ (CP El Nino) or ‘El Nino Modoki’), in which SST anomalies are confined to the central Pacific. Here the vertical structure variability of the periods during EP and CP is investigated based on the GFDL_CM2.1 model in order to explain the difference in equatorial wave dynamics and associated negative feedback mechanisms. It is shown that the mean stratification in the vicinity of the thermocline of the central Pacific is reduced during CP El Nino, which favours the contribution of the gravest baroclinic mode relatively to the higher-order slower baroclinic mode. Energetic Kelvin and first-meridional Rossby wave are evidenced during the CP El Nino with distinctive amplitude and propagating characteristics according to their vertical structure (mostly first and second baroclinic modes). In particular, the first baroclinic mode during CP El Nino is associated to the ocean basin mode and participates to the recharge process during the whole El Nino cycle, whereas the second baroclinic mode is mostly driving the discharge process through the delayed oscillator mechanism. This may explain that the phase transition from warm to neutral/cold conditions during the CP El Nino is delayed and/or disrupted compared to the EP El Nino. Our results have implications for the interpretation of the variability during periods of high CP El Nino occurrence like the last decade.

A record of the Southern Oscillation Index for the past 2,000 years from precipitation proxies

The El Nino-Southern Oscillation (ENSO) is a coupled ocean-atmosphere climate phenomenon in the tropical Pacific Ocean. The interannual climate variations have been shown to modify both the Hadley and Walker meridional and zonal atmospheric circulations, with strong impacts on global climate(1-3). Proxy-based reconstructions of the Southern Oscillation Index on a multi-decadal scale have shown that the strength and frequency of El Nino occurrences have varied over the past millennium(4-7). Here we compile reconstructions of precipitation(8-15) from regions that experience substantial ENSO variability to extend the multidecadal-scale Southern Oscillation Index to include the past 2,000 years. We find that the Medieval Warm Period (similar to AD 800-1300) was characterized by a negative index, which indicates more El Nino-dominated conditions, whereas during the Little Ice Age (similar to AD 1400-1850) more La Nina-dominated conditions prevailed. The Southern Oscillation Index we derive is significantly correlated with reconstructions of solar irradiance and mean Northern Hemisphere temperature fluctuations.

The role of mean state on changes in El Niño’s flavor

Recently, many studies have argued for the existence of two types of El Nino phenomena based on different spatial distributions: the conventional El Nino [or Eastern Pacific (EP) El Nino], and the Central Pacific (CP) El Nino. Here, we investigate the decadal modulation of CP El Nino occurrences using a long-term coupled general circulation model simulation, focusing, in particular, on the role of climate state in the regime change between more and fewer CP El Nino events. The higher occurrence regime of the CP El Nino coincides with the lower occurrence regime of EP El Nino, and vice versa. The climate states associated with these two opposite regimes resemble the leading principal component analysis (PCA) modes of tropical Pacific decadal variability, indicating that decadal change in climate state may lead to regime change in terms of two different types of El Nino. In particular, the higher occurrence regime of CP El Nino is associated with a strong zonal gradient of mean surface temperature in the equatorial Pacific, along with a strong equatorial Trade wind over the area east of the dateline. In addition, the oceanic variables—the mixed layer depth and the thermocline depth—show values indicating increased depth over the western-to-central Pacific. The aforementioned climate states obviously intensify zonal advective feedback, which promotes increased generation of the CP El Nino. Frequent CP El Nino occurrences are not fully described by oceanic subsurface dynamics, and dynamical or thermodynamical processes in the ocean mixed layer and air–sea interaction are important contributors to the generation of the CP El Nino. Furthermore, the atmospheric response with respect to the SSTA tends to move toward the west, which leads to a weak air–sea coupling over the eastern Pacific. These features could be regarded as evidence that the climate state can provide a selection mechanism of the El Nino type.

Propagating Coupled Modes between the Tropical Indo-Pacific Ocean Heat Content and SST Anomalies in the Interannual Timescale

This study uses a time-mode extended singular value decomposition (TESVD) analysis to identify the propagating coupled modes between the upper ocean heat content (UOHC) and sea surface temperature (SST) anomalies in the tropical Indo-Pacific. Four dominant TESVD modes stand out in the interannual timescale. The TESVD1 and TESVD2 depict the thermocline-SST feedback process during ENSO’ persistence period and its turnabout, respectively. With an intrinsic 42-month periodicity, both modes together form an UOHCA pattern propagating counterclockwise around the circuit of equatorial-to-northern tropical Pacific followed by the SSTA propagating eastward in the equatorial waveguide. The leading role of UOHCA is mainly associated with El Nino occurrence. In contrast, the TESVD3 depicts the onset stage of ENSO that has the westward propagating SSTA lead the UOHCA in the cold tongue region. Suppressed equatorial upwelling directly through the positive feedback between the warmer SSTs and anomalous wind convergence from the northwestern Pacific and Caribbean Sea is another factor to trigger El Nino over the NINO3 region, in addition to the thermocline-SST feedback. The TESVD4 depicts the low-frequency evolution of SSTA when ENSO signal is absent. It has the westward migrating SSTA lead the UOHCA 4-month in the equatorial East Pacific. However, the pace of coupled UOHCA is nearly stagnant elsewhere due to the lack of thermocline adjustment mechanism when the zonal wind anomalies largely disappear over the equatorial Indian and West Pacific Oceans. In the Indian Ocean, while the ENSO-related SSTA evolution mainly displays an eastward basin-scale change in the first two TESVD modes, SSTA pattern depicted by the TESVD3 (TESVD4) resembles the double (single) polarity of the Indian Ocean dipole (IOD) event. It is mainly in its east pole region of southeastern Indian Ocean that the SSTA evolution tends to decouple with the underlying UOHCA.

Anomalías de la precipitación pluvial de São Paulo

El objetivo de este trabajo fue analizar la precipitación pluvial del Estado de São Paulo, basado en datos obtenidos junto a la Agencia Nacional de Agua (ANA). El período de análisis fue desde 1974 a 2003. Basado en estos cálculos se puede concluir que las lluvias en el Estado sufren variabilidad espacial, temporal y que la explicación de esta variabilidad espacial está, muchas veces, asociada a la ocurrencia de eventos como El Niño y La Niña.

Late Quaternary climatic changes in southern Chile, as recorded in a diatom sequence of Lago Puyehue (40°40′ S)

A late Quaternary diatom stratigraphy of Lago Puyehue (40°40′ S, 72°28′ W) was examined in order to infer past limnological and climatic changes in the South-Chilean Lake District. The diatom assemblages were well preserved in a 1,122 cm long, 14C-dated sediment core spanning the last 17,900 years, and were in support of an early deglaciation of Lago Puyehue. The presence of a short cold spell in South Chile, equivalent to the Younger Dryas event in the Northern Hemisphere, the Antarctic Cold Reversal in Antarctica, or the Huelmo-Mascardi event in southern South America, was not clearly evidenced in the diatom data, although some climate instability may have occurred between 13,400 and 11,700 cal. yr. BP, and a relatively long period (between 16,850 and 12,810 cal. yr. BP) with low absolute abundances and biovolumes could be tentatively interpreted as a period of low rainfall and/or temperatures. An increase in the moisture supply to the lake was tentatively inferred at 12,810 cal. yr. BP. After 9,550 cal. yr. BP, inferred stronger and longer persisting summer stratification, may have been the result of the higher temperatures associated with an early-Holocene thermal optimum. The mid-Holocene appeared to be characterized by a decrease in precipitation, culminating around 5,000 cal. yr. BP, and rising again after 3,000 cal. yr. BP, likely associated with a previously documented lowered frequency and amplitude of El Nino events. An increase in precipitation during the late Holocene (3,000 cal. yr. BP–present) might have marked subsequent increased frequency of El Nino occurrences, leading to drier summers and slightly moister winters in the area.

Fractal Analysis of the Gray-Scale Intensity Data of Finely Laminated Sediments from Bainbridge Crater Lake, Galápagos

The gray-scale intensity data of finely laminated sediments from Bainbridge Crater Lake, Galapagos, were analyzed in terms of Hurst exponent and fractal dimension. The sediment record preserved in this volcanic maar provides a continuous history of past El Nino/Southern Oscillation (ENSO) events over the last 6200 years. Accelerator mass spectrometry radiocarbon data show that sedimentation rate was not constant for whole core. To take into consideration this fact gray-scale intensity data from analyses of X-radiography images of a 4.1 m long core from this basin were divided into Data 1 and Data 2. Data 1 corresponds to the more recent part of stratigraphic sequence, which was deposited since 3000 yr BP; Data 2 is from the earlier part of record between 6200 and 3000 yr BP. A persistent behavior with a Hurst exponent of H = 0.88 and H = 0.8 was found by power spectrum analysis method for Data 1 and Data 2, respectively. The width method of analysis shows that ENSO fluctuation before 3000 yr BP had a persistent behavior on a time-scale up to 26 years, while the more recent El Nino occurrences have a persistent behavior on a time-scale up to 5.6 years.

Haze in Southeast Asia: Needed Local Actions for a Regional Problem

SoutheastAsia experienced disastrous haze episodes in 1997 and 1998 as a result of natural factors such as the El-Nino occurrence and its attendant drought, which aided desiccation and facilitated high combustibility of forest resources, and human activities such as widespread burning of forests in the lush tropical environment. The human factors that caused the haze are presented in this paper, and the conclusion is that Nature is not guilty. A comprehensive approach that tackles the root causes of the haze problem is suggested. Particularly, socioeconomic problems of the poor who use fire as part of their land management, promulgation and effective enforcement of environmental laws are needed on the one hand to reduce the frequency and magnitude of haze episodes in the future. On the other hand, education of the public on `safe’ behavior during haze episodes is necessary to avert large scale haze-related disasters or to prevent haze from becoming instantly synonymous with disaster in the region.

Manifestations historiques du phénomène El Niño en Amérique du Sud depuis le XVIe siècle

A compilation of documentary data available for almost the last five centuries on climatic anomalies associated to El Nino in South America produced the reference sequence for the study of the ENSO system variability. Revisions of documentary information from Peru and Chile, as well as historical studies in northwestern Argentina and northeastern Brazil, indicate that this sequence of El Nino occurrences is less well-constrained that previously envisioned. The lack of synchronicity observed between manifestations of this phenomenon in several areas of the continent is puzzling and suggests that the teleconnection system varied through time. Actually, the reconstruction of the historical sequence of ENSO events should not yet be viewed as consolidated, and still requires a better understanding of the variability in space and time of the impacts of the phenomenon.