The influence of the opposite phases of ENSO on the frequency of extreme rainfall events over South America is analyzed for each month of the ENSO cycle on the basis of a large set of daily station rainfall data and compared with the influence of ENSO on the monthly total rainfall. The analysis is carried out with station data and their gridded version and the results are consistent. Extreme events are defined as 3-day mean precipitation above the 90th percentile. The mean frequencies of extreme events are determined for each month and for each category of year (El Niñ o, La Niñ a, and neutral), and the differences between El Niñ o and neutral years and La Niñ a and neutral years are computed. Changes in the mean intensity of extreme events are also investigated. Significant ENSO signals in the frequency of extreme events are found over extensive regions of South America during different periods of the ENSO cycle. Although ENSO-related changes in intensity show less significance and spatial coherence, there are some robust changes in several regions, especially in southeastern South America.The ENSO-related changes in the frequency of extreme rainfall events are generally coherent with changes in total monthly rainfall quantities. However, significant changes in extremes are much more extensive than the corresponding changes in monthly rainfall because the highest sensitivity to ENSO seems to be in the extreme range of daily precipitation. This is important, since the most dramatic consequences of climate variability result from changes in extreme events.The pattern of frequency changes produced by El Niñ o and La Niñ a episodes with respect to neutral years is roughly symmetric, but there are several examples of nonlinearity in the ENSO regional teleconnections.

Sea surface temperature (SST) anomalies in the Pacific Ocean during El Niño-Southern Oscillation (ENSO) episodes exhibit different spatial patterns from year to year. In most ENSO studies, SST anomalies have been analysed in the 3.4 or 3.0 El Niño regions. Recent analyses have considered different SST anomalies areas in the Pacific, such as ENSO Modoki, which takes into account anomalies in the central Pacific which are bounded by opposite anomalies in the eastern and western Pacific. In order to analyse the influence of different Pacific spatial patterns on South American precipitation and on the Southern Hemisphere atmospheric circulation, composites obtained from Canonical ENSO were compared with those from ENSO Modoki in cases when strong anomalies were present in the Central Pacific. During the Canonical El Niño (La Niña), there tends to be a precipitation increase (decrease) in the La Plata Basin (LPB, 45°W-65°W, 15°S-35°S) and a decrease (increase) over northern South America during all seasons. In ENSO Modoki exhibiting strong anomalies in the Central Pacific, these typical patterns are not observed, and in some regions the anomalies even show opposite signs. Precipitation anomaly differences or similarities over South America between the two cases occur in different areas and different seasons. In both cases, differences in tropical South American precipitation during both ENSO types are related to differences in the Walker circulation. In extra-tropical South America, the precipitation differences are due to differences in the Pacific wavetrains and differences in moisture flux intensity over the continent.

Recent studies show that different types of ENSO influence the atmospheric fields differently. In this study, precipitation anomalies and extreme events over South America are analysed with relation to two types of ENSO [East (strong Sea Surface Temperature Anomalies (SSTA) on East Pacific) and Central (strong SSTA on Central Pacific)]. The composites of precipitation anomalies, during these two types of ENSO, show that there are different patterns, e.g. during austral summer of Central El Niño (CEN) there are negative precipitation anomalies in eastern Brazil that do not exist in East El Niño (EEN), whereas in southern Brazil there are positive precipitation anomalies during EEN that do not exist in CEN. Furthermore, the anomalies are mostly stronger and more extensive during EEN (Central La Niña -CLN) than in CEN (East La Niña -ELN), although there are some exceptions, such as during austral spring in southern Brazil, where anomalies during CEN (ELN) are stronger than during EEN (CLN). The anomalous frequency of extreme precipitation events shows generally patterns consistent with the anomalous precipitation behaviour, though the patterns are not always coincident, because the regions with significant increase of frequency of extreme events tend to be more extensive than those with increased seasonal precipitation. When the monthly or seasonal atmospheric anomalies associated with a type of ENSO episode are very similar (opposite) to the atmospheric anomalies associated with extreme precipitation in a certain region, then a significant enhancement (suppression) of the frequency of extreme events is observed in that region during this type of episode.

It is known that the El Niño -Southern Oscillation (ENSO) episodes have a great influence on South American precipitation and its extreme events during austral autumn (from March until May, MAM) and winter (from June until August, JJA) that occur after the ENSO peak (normally this happens on austral summer). Recent papers have studied the two types of ENSO and their influence on atmosphere-ocean system. This study analysed the influence of Central and East equatorial Pacific ENSO on South American seasonal/monthly mean precipitation and its extreme events during MAM and JJA. The composites of precipitation anomalies, during these two types of ENSO, show that there are different, even opposite patterns over South America. In MAM, there is an increased precipitation in southeastern South America and a decrease in the northeast South America during East El Niño (EEN) and an increased precipitation in central Brazil during Central El Niño (CEN). In JJA, the signs of anomaly precipitation are opposite between CEN (less precipitation) and EEN (more precipitation) over southeastern South America. The extreme precipitation events show patterns consistent with the precipitation anomaly patterns, but, normally, the changes in the frequency of extremes precipitation events affect more extensive areas than the total precipitation. If monthly or seasonal atmospheric anomalies in a certain region during one of the types of ENSO are similar (opposite) to the atmospheric anomalies associated with extreme precipitation events in this region, then there is enhancement (suppression) of the frequency of extreme events in this region during this type of ENSO.

South American precipitation is observed to respond differently to different types of El Niño Southern Oscillation (ENSO) events, such as those in which the main signal in sea surface temperature (SST) occurs either in the eastern equatorial Pacific or central equatorial Pacific. This study investigates how Coupled Model Intercomparison Project Phase 5 (CMIP5) models represent different types of ENSO and how they represent teleconnections to South American precipitation. It is found that the CMIP5 models can represent the basic structure of SST anomalies that occur during different types of ENSO events and these are described using simple SST indices. Most of the CMIP5 models can reproduce the correct sign of precipitation anomalies in northeast South America during austral summer and autumn, in cases where the observed teleconnections are relatively strong. The same is also true of north South America in austral summer. In the east and southeast regions of South America, many models fail to reproduce the correct sign during both Canonical and Modoki/Central Pacific/Warm Pool ENSO events. The precipitation composites in Atmospheric Model Intercomparison Project (AMIP) models tend to agree with their CMIP5 counterparts, so we conclude that the errors in teleconnections are not principally driven by mean SST biases. Precipitation teleconnections in the northern regions are shown to be linked to variations in the Walker circulation in models, with the exception of that in north South America during March-May. During March-May, composite precipitation in southeast South America is related to wave trains emanating from the equator.

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The teleconnections of different types of El Niño Southern Oscillation (ENSO) to the Indian summer monsoon are investigated in observations and models. We find that, not all regions in India are strongly affected by ENSO, so we focus on two regional teleconnections: (1) a negative rainfall signal around central north east (CNE) India and ‘hilly’ region during El Niño (and vice versa for La Niña) and (2) similar signal for parts of southern peninsular region. Using correlations, it is found that >50% of the fifth phase of the Coupled Model Inter‐comparison Project models capture these two regional teleconnections, with first captured by >80% of models. Furthermore, using a compositing technique that may better capture asymmetries in response to warm and cold events, the authors find that most models again agree on the sign of regional teleconnection around the CNE and hilly region, suggesting the robustness of ENSO signal in that region. The peninsular teleconnection is less well simulated in models. We find a clear connection between the Walker circulation and Indian summer monsoon rainfall around central India in models.

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