South Oscillation Research Articles

The Potential Link Between El Nino and Water Hyacinth Blooms in Winam Gulf of Lake Victoria, East Africa: Evidence from Satellite Imagery

This study evaluates the link between the occurrence of El Nino events in East Africa and water hyacinth blooms in Winam Gulf of Lake Victoria using remote sensing technology. A time-series of the Normalized Difference Vegetation Index (NDVI) analyzed from data acquired by the multispectral Aqua/Terra sensors aboard the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite are used to monitor areal extent and density of the aquatic plants. We related the NDVI derived from MODIS imagery to data on El Nino South Oscillation (ENSO) events that were obtained from NOAA and rainfall data from the study site. Our results from the 11-year time-series data show a statistically significant positive correlation (R = 0.6, P = 0.021) between the occurrence of El Nino events and water hyacinth blooms in Winam Gulf. The proliferation of water hyacinth rafts in Winam Gulf may be a response to dramatic environmental and water quality changes in Lake Victoria. The patterns of impact of ENSO events and rainfall show spatial and temporal variation patterns in the region, depending on the time and space evolution of each individual ENSO event that could explain the differences in general patterns of water hyacinth cover in Lake Victoria during different El Nino events. Although the problems eutrophication and water hyacinth are severe in the Winam Gulf of Lake Victoria some of the solutions to the problem are located several hundreds of kilometers away in the rich agricultural farmlands of the Lake Victoria catchment area. These include better land management practices and strategies aimed at limiting pollution and soil erosion within the lake’s drainage basin.

Climate change features along the Brahmaputra Valley in the past 26 years and possible causes

Through analyzing the changes of averaged temperature and precipitation along the Brahmaputra Valley from 1980 to 2005, and investigating the correlation between atmospheric circulation indices and these changes, the respondence of the Brahmaputra Valley to the global warming had been analyzed in this paper. It is found that the Brahmaputra Valley climate became warmer and wetter from 1980 to 2005, and the change magnitude is higher than that over the whole Tibetan Plateau. Therefore, the respondence of the Brahmaputra valley to the global warming is more evident than that of the whole plateau during the period. The relationship between atmospheric circulation indices and the regional climate change is significant. When North Atlantic Oscillation index is higher in summer, the climate of the Brahmaputra Valley becomes warmer and dryer; vice versa. When South Oscillation index is higher, it becomes warmer and wetter; vice versa.Worthy of note, the results in this study only emphasize some evidence of change in temperature and precipitation over the Brahmaputra Valley during 1980–2005.

Inter-cohort growth variability and its implication for fishery management of the common sardine ( Strangomera bentincki) stock off the coast of south-central Chile

Temporal and spatial variability in somatic growth of small pelagic fish populations has been recently acknowledged in a variety of stocks worldwide. We investigated the inter-cohort variability in length-at-age and somatic growth of the common sardine on the south-central coast of Chile. Using length frequency decomposition analysis of monthly samples from 1990 to 2006, we obtained the mean length-at-age and estimated 15 cohort specific asymptotic growth models (von Bertalanffy) with additional seasonal parameters. Results showed a conspicuous inter-cohort variability in the mean length and growth rate at different life stages throughout the first year of life. Striking anomalies (positive and negative) were observed during the 97/98 ENSO (El Niño South Oscillation), but the mechanisms behind these dynamics are unknown. Nevertheless, we investigated the impact of these variables on the optimal cohort yield. Simulations show that optimal age (month) to begin exploitation varies between cohorts, and a large portion of available cohort is lost by applying fishing mortality in a sub-optimal period. Therefore, monitoring size composition of each incoming cohort and use of an appropriate harvest strategy could help to better manage this resource and optimize fishery benefits.

Impacto de sistemas meteorológicos no regime hídrico do Rio Grande do Sul em 2006

Neste trabalho foram realizadas a determinação e a análise sazonal do Balanço Hídrico (BH) e a análise do impacto dos Sistemas Meteorológicos (SM) no regime hídrico para o Rio Grande do Sul (RS) no ano de 2006. Utilizaram-se, para o cálculo dos BH, dados mensais de 2006 de temperatura média do ar e precipitação pluvial de 16 estações meteorológicas de superfície do Estado. Os métodos propostos por Thornthwaite & Mather (1955) e Thornthwaite (1948) foram usados para calcular os BH e a evapotranspiração, respectivamente. O impacto dos SM no regime hídrico do RS no ano de 2006 foi analisado com dados de ocorrência de Sistemas Frontais (SF), de Sistemas Convectivos de Mesoescala (SCM) e de Eventos com Condição de Tempo Severo (ECTS). A distribuição da precipitação pluvial no RS em 2006 foi uniforme nos quatro períodos do ano, com registro de maior volume pluviométrico na Metade Norte do Estado, onde não ocorreu falta de água em 2006. Na Metade Sul ocorreu falta de água em JFM (Jan, Fev, Mar) e o no litoral em OND (Out, Nov, Dez) neste ano. Os fatores que contribuíram para a disponibilidade d'água durante o ano de 2006 na Metade Norte e falta de água na Metade Sul do RS em JFM e no litoral em OND, foram: a maior frequência de SCM e de ECTS na Metade Norte do RS; a menor frequência de SF neste ano na Metade Sul do RS em relação à normal climatológica e a atuação do fenômeno ENOS (El Niño Oscilação Sul) cuja configuração em 2006 provocou estiagem na região Sul do Brasil.

The role of an extreme flood disturbance on macrophyte assemblages in a Neotropical floodplain

Aquatic macrophytes produce large amounts of organic matter and have an essential structuring role in floodplains. This process highlights the importance of this community to aquatic biodiversity maintenance. We investigated the role of a flood disturbance on the response of macrophyte assemblages in regional and local structuring in the Upper Parana River floodplain. Plant species were recorded before (November 2006) and after (March 2007) an uncommon increase in water level caused by the El Nino South Oscillation, which is considered a disturbance. Samples were taken in lakes and backwaters located in the floodplain and connected to three distinct rivers (that differentiate three sub-systems). Species richness and the assemblage structure of macrophyte patches underwent significant changes after the flood disturbance, depending on the specific sub-system (rivers) to which the lakes were connected. In addition, flood disturbance had a strong impact on community organization at the local scale. However, regionalization with respect to sub-systems remained significant after the flood disturbance. Our results emphasize the importance of connection to the river on macrophyte community composition and richness, and suggest that flood events in the Upper Parana River floodplain disrupt community organization only at fine (local) scales.

Pacific sardine ( Sardinops sagax, Jenyns 1842) landings prediction. A neural network ecosystemic approach

In this study the performances of computational neural networks (CNNs), multiple linear regressions (MLRs) and generalised additive models (GAMs) to predict Pacific sardine ( Sardinops sagax) landings and to analyse their relationships with environmental factors in the north area off Chile were studied. For this purpose several local and global environmental variables and indexes (sea surface temperature, sea level and Ekman transport index in the Chilean coast and, sea surface temperature in the area Niño 3 + 4 and Niño 1 + 2, and the south oscillation index) were considered as inputs or independent variables. Additionally, several CNNs were calibrated and validated adding the anchovy ( Engraulis ringens) landings in the same area as model inputs. The time lags of the variables considered were selected through analysis of the non-linear cross-correlation functions and an alternative form of sensitivity analysis based on the approach of the missing value problem. The analysis of error measures with validation data set showed that the best results were obtained when local and global variables were used separately and combined with anchovy landings. Globally, the best result was given by a CNN with 18 input variables (model CNN 6(II) which only considered global variables and anchovy landings) and 10 neurons in a hidden layer. For this configuration the explained variance was slightly higher to 86% which supposed a standard error of prediction of 7.66%. These results were significantly better than those obtained with MLRs and GAMs. The strong correlation between predicted and observed sardine landings suggests that CNNs captured the trend of the historical data. Also, the generalisation capacity together the sensitivity analysis allowed us to identify the variables with a high weight in the model and partially to interpret the statistical functional relationships between these environmental variables and sardine landings.

Paleotemperature response to monsoon activity in the Japan Sea during the last 160 kyr

Paleo-sea-surface temperatures in the northeastern- and southeastern-parts of the Japan Sea were reconstructed for the last 160 kyr using alkenone temperatures (U K ′ 37-temperatures). U K ′ 37-temperatures at two sites show distinct glacial–interglacial changes during the last 160 kyr except for the interval corresponding to middle MIS 3 to MIS 2. On orbital-timescales, U K ′ 37-temperature tends to be high during MIS 5e, MIS 5c, and MIS 5a, which coincides with the intervals of stronger East Asian summer monsoon activity. The amplitude of temperature fluctuations in the Japan Sea is significantly higher than those in the neighboring seas. We suggest that the SST variation was amplified by the increasing source water (Kuroshio water) temperature and the changes in the volume transport of the Tsushima Warm Current (TWC) and/or the north–south oscillation of the sub-polar front position within the Japan Sea. Millennial-scale temperature fluctuations in the Japan Sea show that the temperature at the northern site was higher than that at the southern site during warmer periods of MIS 5, which is called “temperature reversal.” By analogy with modern oceanography, the temperature reversal could reflect the enhanced volume transport of the TWC and the spatial relationship between the studied site and the branches of the TWC, which is an essential factor in north–south temperature reversal around the eastern Japan Sea. Temperature drops were found at 114 ka, 111 ka, 93 ka, 87 ka, and 77 ka in MIS 5. Those events were associated with an increase in organic carbon and alkenone contents and can be correlated with the abundance peaks of ice-rafted debris (IRD) at Site GH05-1208 in the northern Japan Sea, suggesting that the surface water was cooled by enhanced mixing and consequent upwelling in a stronger winter monsoon regime.

Predominant modes of winter surface wind variability over the Gulf of Alaska

AbstractTwo distinct modes extracted from winter (Dec.–Mar.) monthly mean surface wind variability over the Gulf of Alaska (GOA) and part of the northeast Pacific Ocean have been identified along with their associations with sea surface temperature (SST), coastal downwelling, surface air temperature (SAT) and sea level pressure (SLP). The leading mode of surface wind variability, accounting for 45% of the variance, is characterized by two distinct and alternating modes or their linear combination, and shows strong interannual and interdecadal variations with the transition years in the mid‐1970s and the beginning and late of 1990s. One mode (M1) features a coherent cyclonic or anticyclonic surface wind anomaly in the GOA and part of the northeast Pacific Ocean, and reflects wind field variability related to the intensity of large scale atmosphere‐ocean interactions associated with the Aleutian Low, the Pacific/North American (PNA) pattern, the Pacific decadal oscillation (PDO), and the South Oscillation (SO). This mode significantly influences SAT over the GOA and the entire northeast Pacific and influences downwelling along the eastern and southeastern GOA. It does not significantly influence SST in the northern GOA. The other (M2) characterizes dominant southerly or northerly anomalies, and significantly influences coastal downwelling in the northern and southeastern GOA. It is also correlated with SAT over the GOA, the Bering Sea shelf, and much of Alaska. The impact of M2 on SST is greater than that of M1 in the GOA and the Bering Sea. M1 and M2, respectively, correspond to the PNA pattern and a dipole pattern, and the later is characterized by the third mode of the empirical orthogonal function (EOF) analysis of winter SLP variability over the domain 20° –70°N and 160°E–100°W, accounting for 13% of the variance. The dipole pattern is a new mode of winter atmospheric variability, with opposite anomalous centres over the southern Bering Sea and the west coast of the USA and part of the northeast Pacific Ocean. Copyright © 2009 Royal Meteorological Society

Influence of ENSO on multi‐annual temperature variations at Hongyuan, NE Qinghai‐Tibet plateau: evidence from δ13C of spruce tree rings

AbstractInfluence of ENSO on global temperature variations has aroused wide attention. However, little is known about this effect at regions where different monsoons prevail. In this study, we measured δ13C of spruce trees (picea likiangensis var. rubescens) and reconstructed temperature variations during the past 270 years at Hongyuan, the Zoige plateau where Indian summer monsoon (ISM) dominates. Temperature variation inferred from δ13Ctreering at the Zoige plateau shows anti‐teleconnection on multi‐annual timescales to the sea‐surface temperature (SST) anomaly in the Niño3 region (SSTANiño3 for short) which has been widely used as an indicator of the “El Niño–South Oscillation” (ENSO). We speculate that the ENSO may modulate the regional surface temperature by influencing the intensity of the ISM, which affects the influx of warm/moist air mass to the study region and subsequently changes the latent heating. On multi‐annual scales, when the SSTANiño3 is high (low), the ISM is weak (strong), monsoon precipitation decreases (increase), the latent heating is weakened (strengthened) and surface air temperature is lower (higher). Copyright © 2009 Royal Meteorological Society

Regional characteristics of temperature changes in China during the past 58 years and its probable correlation with abrupt temperature change

Based on recent studies of nonlinear science, we reconstruct dynamics of National Centre of Environment Prediction （NCEP） daily temperature series from 1948 to 2005 of grids located in China with the time-delay method and then analyse the dynamics structure by using dynamical correlation factor exponent Q.Eight significant temperature change regions are obtained. The characteristics of temperature changes and frequencies of extreme temperature in these regions are discussed, and the probable correlations between temperature changes and frequencies of extreme temperature are studied. Results indicate that, 1） the temperature and frequencies of extreme high temperature in ZhunGe’Er and North China both increased during the past 58 years, while frequencies of extreme low temperature in South China decreased. Furthermore, north oscillation, south oscillation, North Pacific oscillation and El Nio-south oscillation have distinct influence on temperature changes in North China, North-East China, west of West-South China and east of West-South China, while El Nio has distinct influence on South China and South East China. 2） The reason for warming during the past 58 years might be the increase of frequencies of extreme high temperature and the decrease of frequencies of extreme low temperature. 3） The abrupt change of extreme high/low temperature in the 1970s is 3—4 years later than that of abrupt temperature change. That is to say, the process of abrupt temperature change might be the inter-grade of extreme temperature from one stationary period to another stationary one.

Корреляционные связи аномалий температуры поверхности Тихого океана и индекса Южного колебания

On the base of monthly averaged archive data of Pacific SST (array British Atmospheric Data Centre HadISST) and South Oscillation Index (SOI) the cross-correlation functions between SSTanomalies and SOI are calculated for the period 1870-2002. It is shown, that spatial distributions of cross-correlation extremes and its lags are connected with the large-scale features of the surface water structure. The lags of the cross-correlation functions between SST and SOI increases in equatorial zone from east to west, in moderate and polar latitudes, vice versa, from west to east. The speed of propagation of the SST anomalies response on the SOI changes is estimated according to cross-correlation lag.

Large scale meteorological phenomena, ENSO and ITCZ, define the Paraná River isotope composition

Summary The Parana River, the second in discharge in South America after the Amazon River and the fifth all over the world, releases an average of more than 17 000 m 3 s −1 into the Del Plata Estuary. In order to assess the causes of variations in its stable isotope composition, 120 monthly grab samples of the Parana River, acquired on a period of 10 years at the river mouth, near Ciudad Universitaria, Buenos Aires, Argentina have been analysed for oxygen and hydrogen stable isotopes. Both, 2 H and 18 O showed periodic variations ( δ 18 O between −7‰ and −3‰; δ 2 H between −44‰ and −15‰) that follow, shifted in ca. 4 months (average transit time of the river), the southward excursions of the intertropical convergence zone (ITCZ). Deuterium excess values ( δ 2 H − 8 δ 18 O) also exhibited large variations (3–18‰) and showed a positive correlation with the El Nino South Oscillation Phenomenon (ENSO) index. ENSO affects the kinetic of the evaporation process of water and modifies the degree in which ITCZ shifts southwards capturing variable amounts of deuterium-rich recycled moisture from the Amazon’s basin, then precipitating on the catchment’s areas of the Parana River.

Methanesulphonic acid (MSA) stratigraphy from a Talos Dome ice core as a tool in depicting sea ice changes and southern atmospheric circulation over the previous 140 years

Firn core methanesulphonic acid (MSA) stratigraphy from Talos Dome (East Antarctica) was compared with anomalies of the satellite-measured sea ice extent (1973–1995) in the Ross Sea and Wilkes Land oceanic sector. In spite of the sparseness of sea ice data, the MSA maxima fit with many positive sea ice anomalies in the Ross Sea. This evidence suggests that marine biogenic activity enhanced by large sea ice cover is an important, but not exclusive, factor in controlling MSA concentration in snow precipitation at Talos Dome. Other than source intensity, differences in regional atmospheric transport mechanisms affect the arrival of MSA-rich aerosol at Talos Dome. To clarify the role of transport processes in bringing biogenic aerosol to Talos Dome, a spectral analysis was applied to the MSA, SOI (South Oscillation Index), and SAM (Southern Annular Mode) record. Synchronicity or phase shift between the chemical signature and atmospheric circulation modes were tested. The variations in the MSA profile have a periodicity of 6.9, 4.9, 3.5, and 2.9 years. The 6.9 and 2.9 year periodicities show a strong positive correlation and are synchronous with corresponding SOI periodicity. This variability could be related to an increase in MSA source intensity (by dimethylsulphide from phytoplanktonic activity) linked to the sea ice extent in the Ross Sea area, but also to an increased strength in transport processes. Both of these factors are correlated with La Niña events (SOI positive values). Furthermore, SAM positive values are related to an increased sea ice extent in the Ross Sea sector and show two main periodicities 3.3 and 3.8 years. These periodicities determine the MSA variability at 3.5 years. However, the effect of intensification of the polar vortex and the consequent reduction in transport process intensity, which reduce the delivery of air masses enriched in MSA from oceanic areas to Talos Dome, make the effect of the SAM on the MSA concentration at Talos Dome less active than the SOI. In this way, snow deposition at the Talos Dome records larger MSA concentration by the combined effects of increased source emissions and more efficient transport processes. The MSA record from Talos Dome can therefore be considered a reliable proxy of sea ice extent when the effect of changes in transport processes in this region of Antarctica is considered. Over the previous 140 years, these conditions occur with a periodicity of 6.9 years.

Prediction model for spring dust weather frequency in North China

It is of great social and scientific importance and also very difficult to make reliable prediction for dust weather frequency (DWF) in North China. In this paper, the correlation between spring DWF in Beijing and Tianjin observation stations, taken as examples in North China, and seasonally averaged surface air temperature, precipitation, Arctic Oscillation, Antarctic Oscillation, South Oscillation, near surface meridional wind and Eurasian westerly index is respectively calculated so as to construct a prediction model for spring DWF in North China by using these climatic factors. Two prediction models, i.e. model-I and model-II, are then set up respectively based on observed climate data and the 32-year (1970–2001) extra-seasonal hindcast experiment data as reproduced by the nine-level Atmospheric General Circulation Model developed at the Institute of Atmospheric Physics (IAP9L-AGCM). It is indicated that the correlation coefficient between the observed and predicted DWF reaches 0.933 in the model-I, suggesting a high prediction skill one season ahead. The corresponding value is high up to 0.948 for the subsequent model-II, which involves synchronous spring climate data reproduced by the IAP9L-AGCM relative to the model-I. The model-II can not only make more precise prediction but also can bring forward the lead time of real-time prediction from the model-I’s one season to half year. At last, the real-time predictability of the two models is evaluated. It follows that both the models display high prediction skill for both the interannual variation and linear trend of spring DWF in North China, and each is also featured by different advantages. As for the model-II, the prediction skill is much higher than that of original approach by use of the IAP9L-AGCM alone. Therefore, the prediction idea put forward here should be popularized in other regions in China where dust weather occurs frequently.

The Influence of the Extratropical Atmospheric Disturbances on ENSO

AbstractThe composite analysis of the 5 major ENSO events since 1980s show that, through the meridional wind anomaly, the extratropical atmospheric disturbances play a role in triggering the occurrence as well as in the development and decay of ENSO. The extratropical atmospheric disturbances interact with ENSO although they are influenced by ENSO. Before the occurrence of ENSO, due to the anticyclonic anomaly in midlatitude of the South Indian Ocean, the anticyclonic anomaly over Australia tends to be enhanced through the dispersion of Rossby wave; In the meantime, the equatorial convergence of the southerly anomaly off the east of Australia and the northerly anomaly in the Philippine excite the onsets of the westerly anomaly in the equatorial western Pacific and the occurrence of ENSO. Afterwards, the cyclonic anomaly in the Southeast Pacific and the associated southerly anomaly further enhance the westerly anomaly in the equatorial middle and eastern Pacific and the development of ENSO. In the mature phase of ENSO, the cyclonic anomaly in the Southeast Pacific together with the South Oscillation is weakened due to the eastward movement of the anticyclonic anomaly to the east of Australia. Moreover, the cyclonic Aleutian anomaly, in particular the wind anomaly in the subtropical North Pacific, enhances the upwelling of sea water and decreases sea surface temperature in the equatorial middle and eastern Pacific, and therefore plays a role in the decay of ENSO.

Efeito dos eventos ENOS e das TSM na variação pluviométrica do semi-árido paraibano

Os efeitos dos eventos ENOS (El Niño Oscilação Sul) e das TSM (temperatura da superfície do mar) do Atlântico sobre a pluviometria do semi-árido paraibano foram avaliados utilizando-se o teste de Wilcoxom-Mann-Whitney, com base nos dados pluviométricos do período 1970/2000, cedidos pelo LMRS-PB (Laboratório de Meteorologia Recursos Hídricos e Sensoriamento Remoto do Estado da Paraíba). Os resultados mostraram haver uma diferença significativa a nível de 5% de probabilidade entre os períodos com e sem influência dos eventos ENOS e das TSM do Atlântico para o Estado. Para os municípios de Sousa (Alto Sertão) e Sumé (Cariri Ocidental) esta diferença também foi de 5%, porém para o município de Picuí (Seridó/Curimataú) ela foi de 10%, evidenciando que os eventos ENOS e as TSM do Atlântico têm influência direta sobre as variações dos valores médios dos índices de precipitação dos municípios avaliados.

Interannual Variation of Summer Subtropical Westerly Jet in East Asia and Its Impacts on the Climate Anomalies of East Asia Summer Monsoon

AbstractThe interannual variability of the subtropical westerly jet over East Asian (EAJS), its impacts on the climate anomalies of East Asian Summer Monsoon, and their possible mechanisms are investigated in this paper. The impacts of south‐north alternation of EAJS concentrate in the Asia‐Australian Monsoon region and the two sides of the climatological positions of EAJS, which is quite different with the atmospheric response to SO (South Oscillation) or ENSO (El Nino‐South Oscillation). The impacts of ENSO concentrate in the middle and east part of the tropical‐extratropical Pacific.There exist two dominant modes of the summer westerly jet in the north hemisphere. The first mode deals with the south‐north alternation of the westerly jet in the Asia‐Pacific area, esp. in the East Asia. The second mode appears in the mid‐east Pacific of 150°E~20°W. The two modes link with two significantly different SST patterns in the Pacific, but they can all influence the intensity of 200 hPa South Asian Anticyclone, esp. the intensity of east part of the South Asian Anticyclone, and which will contribute to the formation of summer floods and droughts in the east part of China.

Interannual variability of Mascarene high and Australian high and their influences on summer rainfall over East Asia

Based on the reanalysis data from NCEP/NCAR and other observational data, interannual variability of Mascarene high (MH) and Australian high (AH) from 1970 to 1999 is examined. It is shown that interannual variability of MH is dominated by the Antarctic oscillation (AAO), when the circumpolar low in the high southern latitudes deepens, the intensity of MH will be intensified. On the other hand, AH is correlated by AAO as well as El Nino and South Oscillation (ENSO), the intensity of AH will be intensified when El Nino occurs. Both correlation analysis and case study demonstrate that summer rainfall over East Asia is closely related to MH and AH. When MH intensifies from boreal spring to summer (i.e. from austral autumn to winter), there is more rainfall over regions from the Yangtze River valley to Japan, in contrast, less rainfall is found over southern China and western Pacific to the east of Taiwan, and most of regions in mid-latitudes of East Asia. Compared with MH, the effect of AH on summer rainfall in East Asia is limited to localized regions, there is more rainfall over southern China with the intensification of AH. The results in this study show that AAO is a strong signal on interannual timescale, which plays an important role in summer rainfall over East Asia. This discovery is of real importance to revealing the physical mechanism of interannual variability of East Asian summer monsoon and prediction of summer precipitation in China.

Influence of Interannual Variability of Antarctic Sea-Ice on Summer Rainfall in Eastern China

Based on the Antarctic sea-ice coverage reanalysis data from the Hadlcy Center and other observational data during the 30-year period from 1969 to 1998, it is shown that Antarctic sea-ice coverage exhibits considerable interannual variability with a complex relation to El Nino and the South Oscillation (ENSO). Besides this, the ice maintains the seasonal persistence of the atmospheric circulation in high latitudes of the Southern Hemisphere. Thus it can be used as a predictor in short-term climate prediction. Both correlation and time series analyses demonstrate that summer rainfall in eastern China is closely related to Antarctic sea-ice coverage. When it is extended during boreal spring through summer, there is more rainfall in the lower reaches of the Yellow River of North China, and in contrast, less rainfall is found in the Zhujiang River basin of South China and Northeast China. A further analysis indicates that this rainfall pattern is related to the intensity of the East Asian summer monsoon caused by interannual variability of Antarctic sea-ice coverage.

Relationship between El Niño /South Oscillation (ENSO) and population outbreaks of some lemmings and voles in Europe

Ecologists have been puzzled by population cycles of lemmings and voles for the over 70 years. At present, our understanding and explanation to this phenomenon remain controversial. Recently, El Nino/South Oscillation has attracted attention of ecologists on its links with population outbreaks of terrestrial animals. This paper aims to investigate the statistical relationship between outbreaks of microtine rodents and ENSO events by scanning available literature. During 1862–1894, outbreaks of Norway lemmings in Norway tended to occur in the Southern Oscillation Index (SOI) peak years or 1 year after the SOI peak years with an approximate significance level (p = 0.057). During 1885–1931, outbreaks of voles in France tended to occur 1 year before the SOI peak years (p = 0.01). During 1946–1993, outbreaks of lemmings and voles in North Finland tended to occur 1 year before the SOI peak years with a significant level (p = 0.022); the peaks of population abundance corresponded well to the SOI trough years (equal to 1 year before the SOI peak years). Outbreaks of common voles in Poland during 1946–1975 tended to occur in the SOI peak years or 1 year before the SOI peak years (p = 0.011), and also tended to occur 1 year before the SOI peak years (p = 0.030). It was also found that the rodent outbreaks in Norway and France, rodent outbreaks in Finland and Poland synchronized well. It was suggested that the ENSO-related climate or food were key factors in causing outbreaks of microtine rodents in Europe.