Impact Of El Nino Southern Oscillation Research Articles

Austral Summer Teleconnections of Indo-Pacific Variability: Their Nonlinearity and Impacts on Australian Climate

Abstract In austral summer, El Niño–Southern Oscillation (ENSO) covaries with the Indian Ocean Basin Mode (IOBM) and with the southern annular mode (SAM). The present study addresses how the IOBM and the SAM modulate the impact of ENSO on Australia. The authors show that the modulating effect of the SAM is limited; in particular, the SAM does not modify the ENSO teleconnection pattern. However, the IOBM extends ENSO-induced convection anomalies westward over northern Australia and over the eastern Indian Ocean, whereby extending the ENSO tropical teleconnection to the northwest of Australia. The IOBM also generates an equivalent-barotropic Rossby wave train through convection anomalies over northern Australia. The wave train shares an anomaly center over the Tasman Sea latitudes with the Pacific–South American (PSA) pattern, shifting the anomaly center of the PSA pattern to within a closer proximity to Australia. There is a strong asymmetry in the IOBM modulating effect. During an IOBM negative phase, which tends to coincide with La Niña events, the rainfall increase is far greater than the reduction during a positive IOBM phase, which tends to coincide with El Niño events. This modulation asymmetry is consistent with an asymmetry in the ENSO–rainfall teleconnection over Australia, in which the La Niña–rainfall teleconnection is stronger than the El Niño–rainfall teleconnection. This asymmetric ENSO–rainfall teleconnection ensures a higher coherence of northern Australia convective anomalies with La Niña or with a negative phase of the IOBM, hence a greater modification of the PSA pattern, underpinning the asymmetric modulating role of the IOBM.

A Strengthened Influence of ENSO on August High Temperature Extremes over the Southern Yangtze River Valley since the Late 1980s

AbstractThe present study investigates the decadal change in the relationship between China high temperature extremes (HTEs) and El Niño–Southern Oscillation (ENSO). It is found that the relationship between the August HTEs in the southern Yangtze River valley (SYRV) and ENSO has strengthened since the late 1980s. Before the late 1980s, the relationship is weak, whereas, after the late 1980s, the August hot-day numbers in the SYRV region tend to be more than normal during El Niño decaying years. During 1988–2008, El Niño–induced August warm SST anomalies are mainly located in the eastern tropical and north Indian Ocean. As a response to the north Indian Ocean warming, the South Asia high extends eastward, and the SYRV is overlain by upper-level easterly anomalies. The cold horizontal temperature advection induced by upper-level easterly anomalies leads to anomalous descent, which is conducive to the occurrence of HTEs through adiabatic warming. During 1966–86, El Niño–induced August warm SST anomalies are mainly distributed in the equatorial central and southwest tropical Indian Ocean. Corresponding to the equatorial Indian Ocean warming, the ascending motion over the Arabian Sea is enhanced, which leads to an anomalous anticyclone over the Middle East through a Rossby wave–type response and in turn an anomalous cyclone over China through a midlatitude wave pattern. The SYRV is controlled by upper-level westerly anomalies, which is not conducive to the occurrence of HTEs since the corresponding horizontal temperature advection and anomalous vertical motion are weak. As such, the impact of ENSO on August SYRV HTEs is weak before the late 1980s.

Impactos do Fenômeno Enos Sobre a Temperatura no Brasil

The variability of Monthly maximum and minimum temperatures of 265 stations components of INMET’s Meteorological Database for Teaching and Research (BDMEP) in the last 50 years was related to variations in the Oceanic Nino Index from NOAA Climate Prediction Center by training an artificial neural network. The results showed that El Nino contributed to the increase of the maximum and minimum temperatures while the reverse occurs in La Nina events, except for the Amazon region. The impact of ENSO (El Nino-Southern Oscillation) in the country is more present in winter and spring. Some locations were chosen to demonstrate the search results: Manaus, Recife, Cuiaba, Brasilia, Sao Paulo and Porto Alegre. In La Nina years there is a decrease in air temperature in almost all regions of Brazil. The impact of ENSO in the country is more observed in winter and spring.

Effect of El Niño on the diet of a specialist seabird, Sula nebouxii, in the warm eastern tropical Pacific

Reductions in the availability of energetically valuable prey associated with the El Nino Southern Oscillation (ENSO) may force seabirds to switch to low-energy prey or smaller prey, with consequent effects on their fitness. Impacts of ENSO on seabird diet have been docu- mented in several regions but remain unexplored in the warm eastern tropical Pacific. Analysis of 5 yr of data on the blue-footed booby Sula nebouxii, a seabird specialized on small pelagic fish, revealed that both sexes switch diet and capture fewer types of prey when warm El Nino condi- tions prevail during the breeding season. Moreover, ENSO-related alternations in the relative abundances of anchovies and herrings, the main prey of these boobies and important commercial fishes in the region, were associated with boobies feeding on more and larger anchovies and fewer and smaller herrings during warm El Nino events, and vice versa during cold La Nina episodes. Females consumed herrings more frequently than males across the 5 yr and consistently fed on larger anchovies and herrings than males, with these differences likely due to this booby's reversed sexual size-dimorphism. We conclude that diet composition and prey size of boobies may be sensitive to variation in relative availabilities of different prey species associated with the ENSO, making these birds robust indicators of environmental fluctuations in the warm eastern tropical Pacific. Inter-annual variations in the availability of herrings, probably the most energet- ically valuable prey for these boobies, may explain the large ENSO-related variations in booby reproduction documented previously.

Asian summer monsoon prediction in ECMWF System 4 and NCEP CFSv2 retrospective seasonal forecasts

The seasonal prediction skill of the Asian summer monsoon is assessed using retrospective predictions (1982–2009) from the ECMWF System 4 (SYS4) and NCEP CFS version 2 (CFSv2) seasonal prediction systems. In both SYS4 and CFSv2, a cold bias of sea-surface temperature (SST) is found over the equatorial Pacific, North Atlantic, Indian Oceans and over a broad region in the Southern Hemisphere relative to observations. In contrast, a warm bias is found over the northern part of North Pacific and North Atlantic. Excessive precipitation is found along the ITCZ, equatorial Atlantic, equatorial Indian Ocean and the maritime continent. The southwest monsoon flow and the Somali Jet are stronger in SYS4, while the south-easterly trade winds over the tropical Indian Ocean, the Somali Jet and the subtropical northwestern Pacific high are weaker in CFSv2 relative to the reanalysis. In both systems, the prediction of SST, precipitation and low-level zonal wind has greatest skill in the tropical belt, especially over the central and eastern Pacific where the influence of El Nino-Southern Oscillation (ENSO) is dominant. Both modeling systems capture the global monsoon and the large-scale monsoon wind variability well, while at the same time performing poorly in simulating monsoon precipitation. The Asian monsoon prediction skill increases with the ENSO amplitude, although the models simulate an overly strong impact of ENSO on the monsoon. Overall, the monsoon predictive skill is lower than the ENSO skill in both modeling systems but both systems show greater predictive skill compared to persistence.

An innovative tailored seasonal rainfall forecasting production in Zimbabwe

Farmers’ adaptation to climate change over southern Africa may become an elusive concept if adequate attention is not rendered to the most important adaptive tool, the regional seasonal forecasting system. Uptake of the convectional seasonal rainfall forecasts issued through the southern African regional climate outlook forum process in Zimbabwe is very low, most probably due to an inherent poor forecast skill and inadequate lead time. Zimbabwe’s recurrent droughts are never in forecast, and the bias towards near normal conditions is almost perpetual. Consequently, the forecasts are poorly valued by the farmers as benefits accrued from these forecasts are minimal. The dissemination process is also very complicated, resulting in the late and distorted reception. The probabilistic nature of the forecast renders it difficult to interpret by the farmers, hence the need to review the whole system. An innovative approach to a regional seasonal forecasting system developed through a participatory process so as to offer a practically possible remedial option is described in this paper. The main added advantage over the convectional forecast is that the new forecast system carries with it, predominantly binary forecast information desperately needed by local farmers—whether a drought will occur in a given season. Hence, the tailored forecast is easier for farmers to understand and act on compared to the conventional method of using tercile probabilities. It does not only provide a better forecasting skill, but gives additional indications of the intra-seasonal distribution of the rainfall including onsets, cessations, wet spell and dry spell locations for specific terciles. The lead time is more than 3 months, which is adequate for the farmers to prepare their land well before the onset of the rains. Its simplicity renders it relatively easy to use, with model inputs only requiring the states of El Nino Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) climate modes. The developed forecast system could be one way to enhance management of risks and opportunities in rain-fed agriculture among small-holder farmers not only in Zimbabwe but also throughout the SADC region where the impact of ENSO and/or IOD on a desired station rainfall is significant.

Relationship between ENSO phases with Northwest India winter precipitation

AbstractWinter (December, January, February and March—DJFM) precipitation variability over Northwestern India is examined in association with large scale global forcing of El Niño Southern Oscillation (ENSO). During winter, Northwestern India receives precipitation in the form of snow, by eastward moving synoptic weather systems—western disturbances (WDs). An attempt is made to define relationship between wintertime large scale atmospheric fields with different phases of ENSO. A composite set of El Niño (10 years) and La Niña (8 years) is prepared to analyse role of large scale fields followed by ENSO response with wintertime precipitation over Northwestern India. Significant correlation between the two indicates increased (decreased) precipitation over Northwestern India during warm (cold) phase of ENSO. Higher geopotential height, with stronger southwesterly to northwesterly wind flow suggests more moisture flux from the Caspian and Arabian Sea. Empirical orthogonal function analysis also suggests instance of ENSO impact on Northwest India winter precipitation. Copyright © 2012 Royal Meteorological Society

Quantification of El Nino Southern Oscillation impact on precipitation and streamflows for improved management of water resources in Alabama

<h3>Objective</h3> Kangaroo Mother Care (KMC) is a frugal innovation improving newborn health at a reduced cost compared with incubator use. KMC is widely recommended; however, in the UK, poor evidence exists on KMC, and its implementation remains inconsistent. <h3>Design</h3> This Systematic Review and Realist Synthesis explores the barriers and facilitators in the implementation of KMC in the UK. <h3>Data source</h3> OVID databases, Cumulative Index to Nursing and Allied Health Literature (CINAHL), Scopus and Google Scholar were searched. <h3>Eligibility criteria</h3> Studies were UK based, in maternity/neonatal units, for full-term/preterm children. First screening included studies on (1) KMC, Kangaroo Care (KC) or skin-to-skin contact (SSC) or (2) Baby Friendly Initiative, Small Wonders Change Program or family-centred care if in relation to KMC/KC/SSC. Full texts were reviewed for evidence regarding KMC/KC/SSC implementation. <h3>Results</h3> The paucity of KMC research in the UK did not permit a realist review. However, expanded review of available published studies on KC and SSC, used as a proxy to understand KMC implementation, demonstrated that the main barriers are the lack of training, knowledge, confidence and clear guidelines. <h3>Conclusion</h3> The lack of KMC implementation research in the UK stands in contrast to the already well-proven benefits of KMC for stable babies in low-income contexts and highlights the need for further research, especially in sick and small newborn population. Implementation of, and research into, KC/SSC is inconsistent and of low quality. Improvements are needed to enhance staff training and parental support, and to develop guidelines to properly implement KC/SSC. It should be used as an opportunity to emphasise the focus on KMC as a potential cost-effective alternative to reduce the need for incubator use in the UK.

Modeling the ENSO impact of orbitally induced mean state climate changes

The sensitivity of the El Niño–Southern Oscillation (ENSO) phenomenon to changes in the tropical Pacific mean climate is investigated with a coupled atmosphere‐ocean‐sea ice general circulation model (AOGCM), the Kiel Climate Model (KCM). Different mean climate states are generated by changing the orbital forcing that causes a redistribution of solar energy, which was a major driver of both the Holocene and the Eemian climates. We find that the ENSO amplitude is positively correlated with both the Equatorial Pacific sea surface temperature (SST) and the equatorial zonal SST contrast. The latter is controlled by the upwelling‐induced damping of the SST changes in the Eastern Equatorial Pacific (EEP), and by the vertical ocean dynamical heating and zonal heat transport convergence in the Western Equatorial Pacific. The ENSO amplitude also correlates positively with the seasonal SST amplitude in the EEP and negatively with the strength of the easterly Trades over the Equatorial Pacific. However, the ENSO period is rather stable and stays within 3–4 years. Enhanced ENSO amplitude is simulated during the late‐Holocene, in agreement with paleoproxy records. The tight positive correlation (r = 0.89) between the ENSO strength and the Western Pacific Warm Pool (WPWP) SST suggests that the latter may provide an indirect measure of the ENSO amplitude from proxy data that cannot explicitly resolve interannual variability.

Spatial-temporal variations of dominant drought/flood modes and the associated atmospheric circulation and ocean events in rainy season over the east of China

By using Season-reliant Empirical Orthogonal Function (S-EOF) analysis, three dominant modes of the spatial-temporal evolution of the drought/flood patterns in the rainy season over the east of China are revealed for the period of 1960–2004. The first two leading modes occur during the turnabout phase of El Nino-Southern Oscillation (ENSO) decaying year, but the drought/flood patterns in the rainy season over the east of China are different due to the role of the Indian Ocean (IO). The first leading mode appears closely correlated with the ENSO events. In the decaying year of El Nino, the associated western North Pacific (WNP) anticyclone located over the Philippine Sea persists from the previous winter to the next early summer, transports warm and moist air toward the southern Yangtze River in China, and leads to wet conditions over this entire region. Therefore, the precipitation anomaly in summer exhibits a ‘Southern Flood and Northern Drought’ pattern over East China. On the other hand, the basin-wide Indian Ocean sea surface temperature anomaly (SSTA) plays a crucial role in prolonging the impact of ENSO on the second mode during the ENSO decaying summer. The Indian Ocean basin mode (IOBM) warming persists through summer and unleashes its influence, which forces a Matsuno-Gill pattern in the upper troposphere. Over the subtropical western North Pacific, an anomalous anticyclone forms in the lower troposphere. The southerlies on the northwest flank of this anticyclone increase the moisture transport onto central China, leading to abundant rainfall over the middle and lower reaches of the Yangtze River and Huaihe River valleys. The anomalous anticyclone causes dry conditions over South China and the South China Sea (SCS). The precipitation anomaly in summer exhibits a ‘Northern Flood and Southern Drought’ pattern over East China. Therefore, besides the ENSO event the IOBM is an important factor to influence the drought/flood patterns in the rainy season over the east of China. The third mode is positively correlated with the tropical SSTA in the Indian Ocean from the spring of preceding year(-1) to the winter of following year(+1), but not related to the ENSO events. The positive SSTA in the South China Sea and the Philippine Sea persists from spring to autumn, leading to weak north-south and land-sea thermal contrasts, which may weaken the intensity of the East Asia summer monsoon. The weakened rainfall over the northern Indian monsoon region may link to the third spatial mode through the ‘Silk Road’ teleconnection or a part of circumglobal teleconnection (CGT). The physical mechanisms that reveal these linkages remain elusive and invite further investigation.

The Effect of ENSO and PDO on Three Airborne Pollutants in Phoenix, Arizona

ABSTRACT Previous research has suggested that the El Nino-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) teleconnections have a large impact on precipitation across the Desert Southwest. El Nino years, particularly those that occur in concert with the warm phase of the PDO, have been associated with increased precipitation while La Nina years have had the opposite effect. There has been very little research examining the impact of teleconnections on pollution in the Southwest. Here, we examine the impact of both ENSO and PDO on winter pollution levels in Phoenix. By first examining the impact of precipitation events on pollution, and then by determining the impact of ENSO and PDO on the number of precipitation events, we can estimate the role of these two teleconnections on winter pollution in Phoenix. We find that ENSO and PDO have a large impact on pollution, with some pollutants increasing over 10% during La Nina compared to years experiencing El Nino.

ENSO connection with monsoon rainfall over Bangladesh

This paper investigates the variability and trends of summer monsoon rainfall over Bangladesh and its relation with ENSO (El Nino Southern Oscillation). The data of rainfall for 30 selected rain gauge stations of Bangladesh have been used over a period of 47 years (1961–2007) collected from Bangladesh Meteorological Department (BMD) and ENSO data have been downloaded from the website of Golden Gate Weather Services, Canada. The data are analyzed using different statistical parameters. The major findings of the study are that the mean monthly rainfall of Bangladesh shows a unimodal pattern throughout the year with highest in July (20%) whereas lowest in January (0.36%). Most of the rainfall occurs in the monsoon season (70.69%). However, the pre-monsoon and post-monsoon rainfall accounts 18.94% and 8.94% respectively. Moreover, the winter is very dry and has 1.53% of the annual rainfall. The coefficient of variation is high in the winter and low in the monsoon season. All Bangladesh mean summer monsoon rainfall is 1616 mm (70.6%) where annual country average rainfall is 2286 mm, and standard deviation and coefficient of variance is 208.9mm and 11.76% respectively. Summer monsoon rainfall widely varies over the geographical areas with lowest in central-western part conversely highest in southeastern part with moderate in northeastern part of the country. The short term variability of the scale 2–4 years is highly dominant. The plots using 5-year moving average data smooth out the high frequency oscillations and the variability of longer time scale are better discerned. The decadal scale variation with time period around 10–11 years and 14–16 years are found to be prominent in the filtered series. The higher time scales of around 20 years are also evident in the pre-monsoon and monsoon rainfall. The trend analysis results show that winter has the trend value of 0.56 mm/year against an annual rainfall of 34.9 mm. The relatively high trends of rainfall are obtained from pre-monsoon and post monsoon (2.14 and 2.12 mm/year). In case of ENSO connection, it is found that there have strong impact of ENSO on the monsoon system of subcontinent scale, though the relationship is weak in case of Bangladesh.

Impact of ENSO on the Atmospheric Variability over the North Atlantic in Late Winter—Role of Transient Eddies

Abstract The dynamical mechanism for the late-winter teleconnection between El Niño–Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO) is examined using the output from a 2000-yr integration of a coupled general circulation model (GCM). The coupled model captures many salient features of the observed behavior of both ENSO and NAO, as well as their impact on the surface climate in late winter. Both the observational and model data indicate more occurrences of negative phase of NAO in late winter during El Niño events, and positive NAO in La Niña episodes. The potential role of high-frequency transient eddies in the above teleconnection is diagnosed. During El Niño winters, the intensified transient disturbances along the equatorward-shifted North Pacific storm track extend their influences farther downstream. The eddy-induced negative height tendencies are found to be more coherent and stronger over North Atlantic than that over North Pacific. These negative height tendencies over the North Atlantic are coincident with the southern lobe of NAO, and thus favor more occurrences of negative NAO events. During those El Niño winters with relatively strong SST warming in eastern equatorial Pacific, the eastward extension of eddy activity is reinforced by the enhanced near-surface baroclinicity over the subtropical eastern Pacific. This flow environment supports a stronger linkage between the Pacific and Atlantic storm tracks, and is more conducive to a negative NAO phase. These model results are supported by a parallel analysis of various observational datasets. It is further demonstrated that these transient eddy effects can be reproduced in atmospheric GCM integrations subjected to ENSO-related SST forcing in the tropical Pacific.

Interannual variability of solar energy generation in Australia

Australia has an abundant solar energy resource that is likely to be used for energy generation on a large scale. Variable sources of electricity generation require knowledge of the nature of their variability at all time scales. This study examines the effect that El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) have on solar radiation in Australia, in order to establish the role for seasonal forecasting of solar power. Calendar years are classified into their ENSO state using a sea surface temperature index. The ERA-Interim and NCEP reanalysis products are then used to estimate the effect of ENSO on global horizontal solar irradiance over the continent. A bootstrap technique is used to obtain confidence regions for the effect in both winter and summer. The main impact of ENSO occurs during winter over a large part of eastern Australia. Little impact was observed over the continent during summer. A similar analysis is conducted for the Indian Ocean Dipole (IOD) to ensure that the observed ENSO effect is not a manifestation of the IOD. This study indicates that the ENSO phenomenon may account for solar energy changes of more than 10% in some locations on a seasonal basis. We show that the solar radiation analysis is directly applicable to solar energy yield. Knowledge of this variability may influence the location of large solar generation plants. Also, there is a potential to predict solar energy a few months ahead by means of seasonal forecasting systems, which would help to assist with planning for electricity grid.

The influence of ENSO on winter rainfall in South Africa

AbstractWhereas the impact of ENSO on the African summer rainfall regions is largely documented and still regularly investigated, little is known about its impact on the winter rainfall regions located at the southwestern and northwestern tips of Africa. Yet, these regions are densely inhabited and are net exporters of high‐quality agricultural products. Here we analyze the relationship between El Niño Southern Oscillation (ENSO) and South Africa austral winter rainfall using a 682 raingauges daily rainfall database documenting the period 1950–1999. The May, June and July (MJJ) seasonal rainfall amount shows a positive correlation with the Niño3.4 index that becomes significant since the so‐called 1976/1977 climate regime shift. Wet spells properties (length, frequency and intensity) at the raingauge scale indicate that high (low) MJJ seasonal rainfall amounts recorded during El Niño (La Niña) events are the result of longer (shorter) wet spells in the Cape Town area and more (less) frequent wet spells north of 33°S. Wet spells with daily rainfall amounts ranging between 10 and 50 mm are also more (less) frequent. Atmospheric dynamics fields during wet spells feature lower (higher) pressure and northwesterly (southerly) wind anomalies in the troposphere over the region. This suggests that rain‐bearing systems are deeper (thinner) and larger (smaller) in extent, and located farther north (south) during El Niño (La Niña) events. Copyright © 2011 Royal Meteorological Society

A multiscalar global evaluation of the impact of ENSO on droughts

[1] In this study we analyzed the influence of the El Nino-Southern Oscillation (ENSO) phenomenon on drought severity at the global scale. A unique aspect of the analysis is that the ENSO influence was quantified using a multiscalar drought indicator, which allowed assessment of the role of the ENSO phases on drought types affecting various hydrological, agricultural and environmental systems. The study was based on ENSO composites corresponding to El Nino and La Nina phases, which were obtained from the winter El Nino 3.4 index for the period 1901–2006. Drought was identified in a multiscalar way using the Standardized Precipitation Evapotranspiration Index (SPEI) and the global SPEIbase data set. The study revealed the differing impacts of the El Nino and La Nina phases on drought severity, the time scales of droughts, and the period of the year when the ENSO phases explained drought variability worldwide. In large areas of America and eastern Europe the role of ENSO events were evident at the shortest time scales (1–3 months) at the beginning of events, but in areas of South Africa, Australia and Southeast Asia the effects were more obvious some months later, and at longer time scales. We also identified areas where severe drought conditions are associated with more than 70% of ENSO events. The persistence of the drought signal at longer time-scales (e.g., 6- or 12-months) is not directly determined by the atmospheric circulation response to the SST anomalies, since the SPEI anomalies will be caused by the cumulative dry conditions in some specific months. Knowledge of how these effects differ as a function of the El Nino and La Nina phases, and how they propagate throughout the drought time scales could aid in the prediction of the expected drought severity associated with the ENSO. Lags detected during the study may help forecasting of dry conditions in some regions up to one year before their occurrence.

Land use changes and impact on coral communities along the central Pacific coast of Mexico

The loss of coral coverage from environmental degradation is a progressive phenomenon that occurs in coral communities around the world. However, the consequences of land use changes and its impact on the state of conservation of coral communities are not yet understood. This study compares the impact of coastal land use changes on four coral communities near rural (Isla Faro and El Zapote) and suburban (Caleta de Chon and Playa Manzanillo) sites in the states of Michoacan and Guerrero, along the central Pacific coast of Mexico. Indicators of environmental degradation in coral communities (sediment deposition, water transparency, total suspended solids, and chlorophyll concentration) show that signs of eutrophication are absent from both rural sites in Michoacan. This absence suggests that human impact is not the main cause of the observed degradation (coral Mortality Index MI = 0.85, a high death coral coverage ~42% and the lowest species richness). Instead, the 1997–1998 El Nino-Southern Oscillation (ENSO) event (the strongest in the last decade) appears to be the major factor in this coral cover decline, as it occurred in the eastern Pacific and other regions of the world. In contrast, coral communities near the suburban sites in Guerrero are well developed, and their coral coverage and species richness (up to 67.7% and 7 species, respectively) are comparable to other major coral communities in this region. Nonetheless, indicators of human-derived degradation in the Guerrero coastal zone near Caleta de Chon and Playa Manzanillo, including high sediment deposition up to 1.2 kg m−2 d−1, low water transparency <5 m, presence of filamentous algae on dead corals and a coral Mortality Index of MI ~0.6 show that human impact is beginning to affect the conservation state of these coral communities, reducing their species richness and coral coverage. Although the ENSO impact on coral communities could be more drastic than the anthropogenic impact, the current study confirms that increased land use changes and coastal erosion are causing progressive coral community degradation. Therefore, land and coastal changes must be rigorously regulated.

ENSO teleconnection impacts on reference evapotranspiration variability in some warm climates of Iran

AbstractThe Southern Oscillation Index (SOI) is an acceptable scientific index for determining the strength of El Niño Southern Oscillation (ENSO) phenomenon. Because of the importance of reference evapotranspiration (ET0) in determining crop water demand, this study was conducted to assess the impacts of different ENSO phases on ET0 variability in some warm climates of Iran. For the estimation of ET0, the daily meteorological variables from a set of stations during a period of 50 years (1957–2006) were used in an aerodynamic energy balance approach and the correlation between SOI and the estimated ET0 values for two scenarios (with and without time lag) was constructed. Using Spearman, Pearson and Mann‐Whitney approaches, the correlation coefficients (r) and the statistically significant relative differences between the mean ET0 values and their corresponding variations in each phase were verified. The results of seasonal ET0 showed that in 54% of the study sites, significant (P &lt; 0.05) correlations between ENSO events and the ET0 variations exist. In the monthly timescale, 88% of the significant SOI‐ET0 correlations experienced positive signs. In most of the cases, the spring and winter ENSO events influenced the ET0 values one or two seasons after the occurrence of the ENSO. On average, the mean monthly ET0 values during El Niño phases were 10.1 and 9.3% lower than the corresponding ET0 values during La Niña and normal phases, respectively. On the contrary, the mean monthly ET0 values during La Niña were 8.4% higher than that in normal phase. It was found that the degree of impact of ENSO on ET0 variability is sensitive to the timescale of analyses. Furthermore, the ET0 variations in warm arid sites were more sensitive to teleconnection impact of ENSO than the humid sites. Copyright © 2010 Royal Meteorological Society

Teleconnection Pathways of ENSO and the IOD and the Mechanisms for Impacts on Australian Rainfall

Abstract Impacts of El Niño–Southern Oscillation (ENSO) and the Indian Ocean dipole (IOD) on Australian rainfall are diagnosed from the perspective of tropical and extratropical teleconnections triggered by tropical sea surface temperature (SST) variations. The tropical teleconnection is understood as the equatorially trapped, deep baroclinic response to the diabatic (convective) heating anomalies induced by the tropical SST anomalies. These diabatic heating anomalies also excite equivalent barotropic Rossby wave trains that propagate into the extratropics. The main direct tropical teleconnection during ENSO is the Southern Oscillation (SO), whose impact on Australian rainfall is argued to be mainly confined to near-tropical portions of eastern Australia. Rainfall is suppressed during El Niño because near-tropical eastern Australia directly experiences subsidence and higher surface pressure associated with the western pole of the SO. Impacts on extratropical Australian rainfall during El Niño are argued to stem primarily from the Rossby wave trains forced by convective variations in the Indian Ocean, for which the IOD is a primary source of variability. These equivalent-barotropic Rossby wave trains emanating from the Indian Ocean induce changes to the midlatitude westerlies across southern Australia, thereby affecting rainfall through changes in mean-state baroclinicity, west–east steering, and possibly orographic effects. Although the IOD does not mature until austral spring, its impact on Australian rainfall during winter is also ascribed to this mechanism. Because ENSO is largely unrelated to the IOD during austral winter, there is limited impact of ENSO on rainfall across southern latitudes of Australia in winter. A strong impact of ENSO on southern Australia rainfall in spring is ascribed to the strong covariation of ENSO and the IOD in this season. Implications of this pathway from the tropical Indian Ocean for impacts of both the IOD and ENSO on southern Australian climate are discussed with regard to the ability to make seasonal climate predictions and with regard to the role of trends in tropical SST for driving trends in Australian climate.

The impact of ENSO and the Arctic Oscillation on winter temperature extremes in the southeast United States

Interannual variations of the winter mean temperature and the number of days of warm and cold extremes were investigated for the southeast United States to identify the relative influence of El Niño‐Southern Oscillation (ENSO) and the Arctic Oscillation (AO). Generalized extreme value theory was used to estimate the probability distribution function (PDF) of warm and cold extremes and their return values for different phases of ENSO and the AO. An analysis of the temperature observations for the past 58 years (1951–2008) reveals that both the winter mean temperature anomalies and the number of days of extreme cold are most closely linked to variations in the AO especially in the recent past (1981–2008). In contrast, the number of days of extreme warmth are linked to both ENSO and the AO.