共查询到20条相似文献，搜索用时 406 毫秒
1.
Małgorzata Świerczyńska Tomasz Niedzielski Wiesław Kosek 《Studia Geophysica et Geodaetica》2014,58(2):302-325
The purpose of this paper is twofold. First, we demonstrate that the asymmetry between El Niño and La Niña events recorded in sea level variation occurs only during extreme episodes of El Niño/Southern Oscillation. Second, we explain that the asymmetry is controlled by certain regular cycles which have time-variable amplitudes. Gridded maps of sea level anomaly that form a spatial-temporal time series (spatial resolution: 1° × 1°, sampling interval: 1 week) spanning the time interval from 14/10/1993 to 18/04/2012 were used. We examined those time series and found that certain regular harmonic signals (periods: 365, 182, 120, 90 and 62 days) are dominant terms of their temporal variability. By subtracting those oscillations from sea level anomaly data, residuals were determined. Using skewness and kurtosis as measures of asymmetry and nonlinearity — after adopting 10-year moving window — we found that the extreme El Niño 1997/1998 has been a dominant driving force of the asymmetry and nonlinearity of El Niño/Southern Oscillation since the end of 1993. In order to detect residual signals that are responsible for the asymmetry, we applied the Fourier Transform Band Pass Filter and found that there are two important oscillations remaining in the residual sea level anomaly data, i.e. the annual and semiannual ones with time-varying amplitudes. We hypothesize that temporarily uneven amplitudes have meaningful impact on the aforementioned asymmetry. 相似文献
2.
The influence of the El Niño Southern Oscillation (ENSO) phenomenon on monthly mean river flows of 12 rivers in the extreme south of South America in the 20th century is analysed. The original dataset of each river is divided into two subsets, i.e. warm ENSO events or El Niño, and cold ENSO events or La Niña. The elements of the subsets are composites of 24 consecutive months, from January of the year when the ENSO event begins to December of the following year. The ENSO signal is analysed by comparing the monthly mean value of each subset to the long-term monthly mean. The results reveal that, in general, monthly mean El Niño (La Niña) river flows are predominantly larger (smaller) than the long-term monthly mean in the rivers studied. The anomalies are more evident during the second half of the year in which the event starts and the first months of the following year. 相似文献
3.
J. Kelman A. de M. Vieira J. E. Rodriguez-Amaya 《Stochastic Environmental Research and Risk Assessment (SERRA)》2000,14(2):123-138
Stochastic models are often fitted to historical data in order to produce streamflow scenarios. These scenarios are used
as input data for simulation/optimization models that support operational decisions for water resource systems. The streamflow
scenarios are sampled from probability distributions conditioned on the available information, such as recent streamflow data.
In this paper we introduce a procedure for further conditioning the probability distributions by considering the recent measurements
of climatic variables, such as sea temperatures, that are used to describe the occurrence of El Ni?o. We adopt an auto-regressive
model and use the “El Ni?o information” to refine the parameter estimation process for each time step. The corresponding methodology
is tested for the monthly energy time series, “inflowing” to the power plants of Colombia. This is a linear combination of
streamflow values for the 18 most important rivers of the country. 相似文献
4.
Influence of SOI, DMI and Niño3.4 on South Australian rainfall 总被引：1，自引：0，他引：1
Rezaul K. Chowdhury Simon Beecham 《Stochastic Environmental Research and Risk Assessment (SERRA)》2013,27(8):1909-1920
The influences of climate drivers (SOI, DMI and Niño3.4) on South Australian (SA) rainfall are investigated in this study. Recent records of monthly rainfall and climate driver index values from 1981 to 2010 were analysed for 53 rainfall stations, located across eight SA natural resources management (NRM) regions. The Pearson, Kendall and Spearman correlation tests were applied between rainfall and climate drivers and between the climate drivers themselves. Both SA summer (December to February) and autumn (March to May) rainfalls were found not significantly influenced by climate indices. Winter rainfall in the south and east parts of SA was found strongly influenced by both SOI and DMI, particularly in July and August. Both SOI and DMI are inter-correlated in winter. Spring rainfall was found significantly influenced by DMI in the south and east parts of SA, particularly in September and October. In terms of ENSO phenomena, whilst both SOI and Niño3.4 are correlated, SOI was found more to be influential than Niño3.4 for SA winter and spring rainfall. Outcomes of the study are useful for stochastic rainfall generation and for developing downscaling techniques to generate rainfall projections in the region. 相似文献
5.
6.
《Journal of Atmospheric and Solar》1999,61(18):1325-1346
The 1997–1998 El Niño was the strongest in known history. However, its effects on rainfall in different parts of the globe were not all as expected (floods were expected in some regions and droughts in others). The characteristics of this El Niño, and the expected and observed precipitation effects are described; the reasons for the expectations not coming true in some regions are discussed. This paper attempts to review the important scientific issues involved in El Niño phenomena for the general reader. 相似文献
7.
A Lagrangian analysis was applied to the outputs of a coupled physical-biogeochemical model to describe the redistribution of nitrate-rich and nitrate-poor surface water masses in the tropical Pacific throughout the major 1997 El Niño. The same tool was used to analyze the causes of nitrate changes along trajectories and to investigate the consequences of the slow nitrate uptake in the high nutrient low chlorophyll (HNLC) region during the growth phase of the event. Three patterns were identified during the drift of water masses. The first mechanism is well known along the equator: oligotrophic waters from the western Pacific are advected eastward and retain their oligotrophic properties along their drift. The second concerns the persistent upwelling in the eastern basin. Water parcels have complex trajectories within this retention zone and remain mesotrophic. This study draws attention to the third process which is very specific to the HNLC region and to the El Niño period. During the 1997 El Niño, horizontal and vertical inputs of nitrate decreased so dramatically that nitrate uptake by phytoplankton became the only mechanism driving nitrate changes along pathways. The study shows that because of the slow nitrate uptake characteristic of the tropical Pacific HNLC system, nitrate in the pre-El Niño photic layer can support biological production for a period of several months. As a consequence, the slow nitrate uptake delays the gradual onset of oligotrophic conditions over nearly all the area usually occupied by upwelled waters. Owing to this process, mesotrophic conditions persist in the tropical Pacific during El Niño events. 相似文献
8.
We analyzed the relationship between the earth’s rotational variation and sea-surface temperature anomaly. By means of using Fast Fourier Transform (FFT) bandpass filter on the change of length-of-day (ΔLOD) data, the interannual variation series having time periods greater than 1.5-year and less than 8-year was obtained. Time series analyses of the interannual variation, which corresponds to the El Niño period, reveal a close linkage between the earth’s rotation and El Niño. A detailed comparison suggests, that six of seven El Niño events are nearly synchronous with the interannual variation of the earth’s rotation, and all ΔLOD peak are in El Niño years except 1991–92, which means the interannual variation of the earth’s rotation in these years is relatively slow. The correlation between ΔLOD and sea-surface temperature is about 0.517 (1 month-lag), which far exceeds the 99% significance level. 相似文献
9.
J. S. Bailey 《Annales Geophysicae》1998,16(11):1523-1526
I report the discovery of a low frequency temperature oscillation in the eastern North Atlantic (NA), which was significantly correlated with the Southern Oscillation Index (SOI) in the tropical Pacific, but led the latter index by a number of months. This discovery is significant, because it demonstrates a link between the tropical Pacific and the high northerly latitudes which cannot readily be explained in terms of El Niño/Southern Oscillation (ENSO) feedbacks from the tropics, and opens up the possibility that ENSO and temperature anomalies in northerly climes, may actually have a common origin within, or even external to, the global climate system. 相似文献
10.
AbstractReservoir operation is studied for the Daule Peripa and Baba system in Ecuador, where El Niño events cause anomalously heavy precipitation. Reservoir inflow is modelled by a Markov-switching model using El Niño–Southern Oscillation (ENSO) indices as input. Inflow is forecast using 9-month lead time ENSO forecasts. Monthly reservoir releases are optimized with a genetic algorithm, maximizing hydropower production during the forecast period and minimizing deviations from storage targets. The method is applied to the existing Daule Peripa Reservoir and to a planned system including the Baba Reservoir. Optimized operation is compared to historical management of Daule Peripa. Hypothetical management scenarios are used as the benchmark for the planned system, for which no operation policy is known. Upper bounds for operational performance are found via dynamic programming by assuming perfect knowledge of future inflow. The results highlight the advantages of combining inflow forecasts and storage targets in reservoir operation.
Editor D. Koutsoyiannis; Associate editor I. Nalbantis 相似文献
11.
Tomasz Niedzielski 《Pure and Applied Geophysics》2011,168(5):871-886
The objective of the work discussed in this paper was to seek possible links between surface hydrology in Southwestern (SW) Poland and El Niño/Southern Oscillation (ENSO). Although the impact of ENSO on hydrology in Europe has been investigated by many researchers, no clear picture demonstrating spatial variability of such a teleconnection has yet been unequivocally reported. In particular, there is no comprehensive study on ENSO–streamflow links for Polish rivers. Herein, discharge time series from 15 sites located at lowland and mountain rivers in SW Poland and different ENSO indices are examined. They include atmospheric time series (axial component of atmospheric angular momentum, Southern Oscillation Index), oceanic indices (Niño 3.4 Index, Global SST Index), geodetic data (length-of-day), and the combined index (Multivariate ENSO Index). The data span the period from November 1971 to October 2006. On the basis of cross-correlation and wavelet analyses it was found that there is a weak but significant link between ENSO and surface hydrology in SW Poland. It is inferred that ENSO episodes may be among a few factors affecting winter and early spring discharges of rivers in SW Poland and may have a (probably limited) impact on snow-melt flood generation. 相似文献
12.
Science China Earth Sciences - The effects of spring soil moisture over the vast region from the lower and middle reaches of the Yangtze River valley to North China (YRNC) and El Niño on the... 相似文献
13.
We used climatological composite analysis to investigate El Ni?o-Southern Oscillation (ENSO) signals in long-term shallow ground water level observations from four wells in the lower Fraser Valley of British Columbia. Significance of differences between warm-phase, cold-phase, and neutral climate states was assessed with a Monte Carlo bootstrap technique. We also considered time series of local precipitation and streamflow for comparison. Composite annual hyetographs suggest that ENSO precipitation impacts are largely limited to winter and spring, with higher and lower rainfall occurring, respectively, under cold-phase and warm-phase episodes. This is consistent with prior work in the region and is found to be directly reflected in both streamflow and ground water level data. The mean magnitude of ENSO terrestrial hydrologic anomalies can be up to approximately 50% of the average seasonal cycle amplitude. ENSO does not appear to systematically affect annual hydrometeorological cycle timing in this study area. However, relative to the surface hydrologic systems considered, aquifers are observed to retain a stronger memory of seasonal ENSO-related precipitation anomalies, with changes potentially extending through the following summer, presumably reflecting storage effects. Most responses appear to be somewhat nonlinear. 相似文献
14.
15.
Takuya Hasegawa Kentaro Ando Keisuke Mizuno Roger Lukas Bunmei Taguchi Hideharu Sasaki 《Ocean Dynamics》2010,60(5):1255-1269
We investigate the relationship between sea surface temperature (SST) cooling and upwelling along Papua New Guinea’s (PNG) north coast before the onset of El Niño events using a hindcast experiment with a high-resolution ocean general circulation model. Coastal upwelling and related SST cooling appear along PNG north coast during the boreal winter before the onsets of six El Niño events occurring during 1981–2005. Relatively cool SSTs appear along PNG north coast during that time, when anomalous northwesterly surface wind stress, which can cause coastal upwelling by offshore Ekman transport appearing over the region. In addition, anomalous cooling tendencies of SST are observed, accompanying anomalous upward velocities at the base of the mixed layer and shallow anomalies of 27°C isotherm depth. It is also shown that entrainment cooling plays an important role in the cooling of the mixed layer temperature in this region. 相似文献
16.
《Journal of Atmospheric and Solar》1999,61(17):1307-1319
During the contemporaneous interval of 1796–1882 a number of significant decreases in temperature are found in the records of Central England and Northern Ireland. These decreases appear to be related to the occurrences of El Niño and/or cataclysmic volcanic eruptions. For example, a composite of residual Central England temperatures, centering temperatures on the yearly onsets of 20 El Niño events of moderate to stronger strengths, shows that, on average, the change in temperature varied by about ±0.3°C from normal, being warmer during the boreal fall–winter leading up to the El Niño year and cooler during the spring–summer of the El Niño year. Also, the influence of El Niño on Central England temperatures appears to have lasted about 1–2 years. Similarly, a composite of residual Central England temperatures, centering temperatures on the month of eruption for 26 cataclysmic volcanic eruptions, shows that, on average, the temperature decreased by about 0.1–0.2°C, typically, 1–2 years after the eruption; although for specific events, like Tambora, the decrease was considerably greater. Additionally, tropical eruptions appear to have produced greater cooling than extratropical eruptions, and eruptions occurring in boreal spring–summer appear to have produced greater cooling than those occurring in fall–winter. 相似文献
17.
《水文科学杂志》2013,58(6):1006-1020
AbstractThis paper aims to compare the shift in frequency distribution and skill of seasonal climate forecasting of both streamflow and rainfall in eastern Australia based on the Southern Oscillation Index (SOI) Phase system. Recent advances in seasonal forecasting of climate variables have highlighted opportunities for improving decision making in natural resources management. Forecasting of rainfall probabilities for different regions in Australia is available, but the use of similar forecasts for water resource supply has not been developed. The use of streamflow forecasts may provide better information for decision-making in irrigation supply and flow management for improved ecological outcomes. To examine the relative efficacy of seasonal forecasting of streamflow and rainfall, the shift in probability distributions and the forecast skill were evaluated using the Wilcoxon rank-sum test and the linear error in probability space (LEPS) skill score, respectively, at three river gauging stations in the Border Rivers Catchment of the Murray-Darling Basin in eastern Australia. A comparison of rainfall and streamflow distributions confirms higher statistical significance in the shift of streamflow distribution than that in rainfall distribution. Moreover, streamflow distribution showed greater skill of forecasting with 0–3 month lead time, compared to rainfall distribution. 相似文献
18.
Fuchs R Dupouy C Douillet P Caillaud M Mangin A Pinazo C 《Marine pollution bulletin》2012,64(8):1596-1613
In view of increasing environmental awareness and biodiversity conservation, understanding the main forcing mechanism driving biogeochemical cycles in coral reefs and lagoon coastal areas is a priority. La Ni?a events cause unbalanced situations in the Equatorial Pacific and result in enhanced precipitation in South West Pacific coastal areas. We investigated the impact of heavy rainfalls during the 2008 La Ni?a event on the New Caledonia lagoon using a 3D coupled on-line hydrodynamic-biogeochemical model. Simulations and data showed that the whole lagoon was impacted by river inputs and stronger hydrodynamics, enhancing chlorophyll-a concentration by a factor between 1.7 and 1.9. The coupled model provided new insights into plume transport, highlighting that eastern plumes can be advected northwards or can reach the South West Lagoon, depending on the balance between regional, tide-induced, and wind-induced surface currents. It also provided a synoptic view of lagoon biogeochemical-hydrodynamic response, when remote sensing data are not available due to cloud coverage. 相似文献
19.
Simulation outputs were used to contrast the distinct evolution patterns between two types of El Niño. The modeled isotherm depth anomalies closely matched satellite sea surface height anomalies. Results for the El Niño Modoki (central Pacific El Niño) corresponded well with previous studies which suggested that thermocline variations in the equatorial Pacific contain an east–west oscillation. The eastern Pacific El Niño experienced an additional north–south seesaw oscillation between approximately 15° N and 15° S. The wind stress curl pattern over the west-central Pacific was responsible for the unusual manifestation of the eastern Pacific El Niño. The reason why the 1982/1983 El Niño was followed by a normal state whereas a La Niña phase developed from the 1997/1998 El Niño is also discussed. In 1997/1998, the Intertropical Convergence Zone (ITCZ) retreated faster and easterly trade winds appeared immediately after the mature El Niño, cooling the sea surface temperature in the equatorial Pacific and generating the La Niña event. The slow retreat of the ITCZ in 1982/1983 terminated the warm event at a much slower rate and ultimately resulted in a normal phase. 相似文献
20.
Tropical cyclone activity in the northwestern Pacific associated with decaying Central Pacific El Niños 总被引：1，自引：1，他引：0
Jong-Suk Kim Seon Tae Kim Lei Wang Xin Wang Young-Il Moon 《Stochastic Environmental Research and Risk Assessment (SERRA)》2016,30(5):1335-1345
In this study, a comparative analysis was performed to reveal the relationship between the three types of temporal evolution of the Central Pacific (CP) El Niño (prolonged, abrupt, and symmetric decay) in the tropical Pacific Ocean and tropical cyclone (TC) activity in the Western North Pacific (WNP). TCs in the WNP were found to be sensitive to the different types of temporal evolution of the CP El Niño. During years of prolonged and symmetric decay, TCs were more frequent over East Asia with relatively strong TCs. In contrast, during years of abrupt decay, weak TCs with a relatively short lifespan more likely formed at slightly higher latitudes. The historical record of CP El Niño events is limited, but this study is expected to improve the understanding of complex natural systems and provide fundamental information for the scientific understanding and forecasting of TCs. 相似文献