And The Antarctic Oscillation Research Articles

Contributions of Initial Conditions and Meteorological Forecast to Subseasonal-to-Seasonal Hydrological Forecast Skill in Western Tropical South America

Abstract Hydrological predictions at subseasonal-to-seasonal (S2S) time scales can support improved decision-making in climate-dependent sectors like agriculture and hydropower. Here, we present an S2S hydrological forecasting system (S2S-HFS) for western tropical South America (WTSA). The system uses the global NASA Goddard Earth Observing System S2S meteorological forecast system (GEOS-S2S) in combination with the generalized analog regression downscaling algorithm and the NASA Land Information System (LIS). In this implementation study, we evaluate system performance for 3-month hydrological forecasts for the austral autumn season (March–May) using ensemble hindcasts for 2002–17. Results indicate that the S2S-HFS generally offers skill in predictions of monthly precipitation up to 1-month lead, evapotranspiration up to 2 months lead, and soil moisture content up to 3 months lead. Ecoregions with better hindcast performance are located either in the coastal lowlands or in the Amazon lowland forest. We perform dedicated analysis to understand how two important teleconnections affecting the region are represented in the S2S-HFS: El Niño–Southern Oscillation (ENSO) and the Antarctic Oscillation (AAO). We find that forecast skill for all variables at 1-month lead is enhanced during the positive phase of ENSO and the negative phase of AAO. Overall, this study indicates that there is meaningful skill in the S2S-HFS for many ecoregions in WTSA, particularly for long memory variables such as soil moisture. The skill of the precipitation forecast, however, decays rapidly after forecast initialization, a phenomenon that is consistent with S2S meteorological forecasts over much of the world.

The Relationship Between the Zonal Index and Annular Mode Index in Reanalysis and CMIP5 Models

The annular mode at the surface, referred to as the Arctic Oscillation (AO) in the Northern Hemisphere and the Antarctic Oscillation (AAO) in the Southern Hemisphere, is statistically defined by the leading mode of variability of sea level pressure (SLP) or geopotential height. Its principal component time series is set as the AO or AAO index. Although this metric is widely used, it needs an empirical orthogonal function analysis which introduces the complexity in the multi-model analysis. As an alternative measure, the zonal index (ZI), which is traditionally defined as the zonal-mean SLP difference between the two reference latitudes, has also been used. Here we re-evaluate the interannual and trend relationships between the ZI and the AO/AAO index using the two reanalysis datasets and 35 climate model simulations for both the present and future climate. For all datasets, the spatio-temporal variability of the Southern-Hemisphere ZI is almost identical to that of the AAO index. The ZI is still useful to examine the AO-related circulation variability and change in the Northern Hemisphere but mostly in the cold season. The data-dependent ZI, optimized for each data, exhibits a rather weak relationship with the AO index. This result suggests that the interannual variability and long-term trend of the midlatitude circulation can be concisely quantified by computing the fixed-latitude ZI in all seasons in the Southern Hemisphere and in the cold season in the Northern Hemisphere, not only for reanalysis data but also for climate model datasets which have significant biases varying from model to model.

Interhemispheric Synchronization Between the AO and the AAO

AbstractTeleconnections between lower and higher latitude regions are widely known in both the Northern and Southern Hemispheres. To broaden our view of these teleconnections, we searched a reanalysis data set for evidence of a teleconnection between the Arctic Oscillation (AO) and the Antarctic Oscillation (AAO), two widely separated circumpolar phenomena. Statistical analysis of the Japanese 55‐year reanalysis data set showed significant in‐phase synchronization between the AO and AAO, particularly in October and February, with a vertical structure extending from the troposphere to the stratosphere. This vertical structure may suggest a stratospheric control, and we did not find a significant signature indicating a tropical ocean control. We also observed decadal‐scale modulation of the synchronicity. Observational evidence implies that the stratospheric meridional circulation may be responsible for AO‐AAO synchronization.

Temporal Variability of MODIS Phenological Indices in the Temperate Rainforest of Northern Patagonia

Western Patagonia harbors unique and sparsely studied terrestrial ecosystems that are threatened by land use changes and exposure to basin-scale climatic variability. We assessed the performance of two satellite vegetation indices derived from MODIS–Terra, EVI (Enhanced Vegetation Index) and NDVI (Normalized Difference Vegetation Index), over the northern and southern sectors of the Chiloé Island System (CIS) to advance our understanding of vegetation dynamics in the region. Then we examined their time-varying relationships with two climatic indices indicative of tropical and extratropical influence, the ENSO (El Niño–Southern Oscillation) and the Antarctic Oscillation (AAO) index, respectively. The 17-year time series showed that only EVI captured the seasonal pattern characteristic of temperate regions, with low (high) phenological activity during Autumn-Winter (Spring–Summer). NDVI saturated during the season of high productivity and failed to capture the seasonal cycle. Temporal patterns in productivity showed a weakened seasonal cycle during the past decade, particularly over the northern sector. We observed a non-stationary association between EVI and both climatic indices. Significant co-variation between EVI and the Niño–Southern Oscillation index in the annual band persisted from 2001 until 2008–2009; annual coherence with AAO prevailed from 2013 onwards and the 2009–2012 period was characterized by coherence between EVI and both climate indices over longer temporal scales. Our results suggest that the influence of large-scale climatic variability on local weather patterns drives phenological responses in the northern and southern regions of the CIS. The imprint of climatic variability on patterns of primary production across the CIS may be underpinned by spatial differences in the anthropogenic modification of this ecosystem, as the northern sector is strongly modified by forestry and agriculture. We highlight the need for field validation of satellite indices around areas of high biomass and high endemism, located in the southern sector of the island, in order to enhance the utility of satellite vegetation indices in the conservation and management of austral ecosystems.

Large scale climate drivers for wind resource in Southern South America

The relationship between the wind resource in Southern South America (SSA) and the Antarctic Oscillation (AAO) and El Niño/Southern Oscillation (ENSO) is analyzed in this paper. Daily, monthly, seasonal and annual correlations were calculated between wind speeds at 50 m height derived from MERRA reanalysis and the indices of the mentioned climate drivers. Our results shows that the AAO exerts a significant control over wind speeds on inter annual and seasonal timescales. This relation is stronger during spring and summer, with negative correlations over northern Patagonia, the Argentine and Uruguayan Pampas and Paraguay. ENSO shows weaker relations with wind speeds, mainly on the monthly timescale, with negative correlations over Central Argentina; and during spring, with negative correlations over Southern Patagonia. The relations between AAO and wind speeds are relevant in the context of projected climate changes in the region over the next decades. ENSO might be used as a predictor of wind energy production over monthly and seasonal timescales (mainly during spring) in central Chile and Argentina, and Southern Patagonia.

Atmospheric hydrological cycles in the Arctic and Antarctic during the past four decades

Atmospheric hydrological cycles over the Arctic and Antarctic have been investigated in the previous studies and there are some similarity and dissimilarity in the two polar regions. The Arctic and Antarctic are areas of moisture flux convergence through the year. So the precipitation (P) exceeds the evaporation (E) and the net precipitation (P-E) is positive. Therefore, the atmospheric moisture transport is a primary input of water into the polar regions. Meanwhile the climatological seasonal cycles of P-E over these regions are dominated by transient moisture flux associated with cyclone activities, the interannual variations are governed by the stationary flux associated with the Arctic Oscillation and the Antarctic Oscillation (AAO). In addition, recent climate changes influence the polar hydrological cycles. Our analyses using an atmospheric reanalysis up to recent years indicated that there were no significant long-term changes in the poleward moisture transport into both the Arctic and Antarctic during 1979-2016. On the other hand, the water vapor (precipitable water) were clearly increasing over the Arctic and gradually decreasing over the Antarctic during the same period. As expected, the increasing trend of water vapor was due to the large warming over the Arctic. There were two reasons for the gradually decreasing trend of water vapor over the Antarctic. The first one was the positive trend of AAO in summer and the second was deepening trend of the Amundsen low in autumn. The trends in water vapor and temperature during the past 38 years further suggest that both polar regions were getting dryer in several seasons. The trend, however, needs to be confirmed by follow-up climatological analyses.

Long‐term predictability of soil moisture dynamics at the global scale: Persistence versus large‐scale drivers

AbstractHere we investigate factors that influence the long lead time predictability of soil moisture variability using standard statistical methods. As predictors we first consider soil moisture persistence only, using two independent global soil moisture data sets. In a second step we include three teleconnection indices indicative of the main northern, tropical, and southern atmospheric modes, i.e., the North Atlantic Oscillation (NAO), the Southern Oscillation Index (SOI), and the Antarctic Oscillation (AAO). For many regions results show significant skill in predicting soil moisture variability with lead times up to 5 months. Soil moisture persistence plays a key role at monthly to subseasonal time scales. With increasing lead times large‐scale atmospheric drivers become more important, and areas influenced by teleconnection indices show higher predictability. This long lead time predictability of soil moisture may help to improve early warning systems for important natural hazards, such as heat waves, droughts, wildfires, and floods.

Satellite-measured interannual variability of turbid river plumes off central-southern Chile: Spatial patterns and the influence of climate variability

Ocean color imagery from MODIS (Moderate Resolution Imaging Spectroradiometer) onboard the Aqua platform is used to characterize the interannual variability of turbid river plumes off central-southern Chile. Emphasis is placed on the influence of climate fluctuations, namely El Niño Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and the Antarctic Oscillation (AAO). Additional satellite data on wind, boat-based hydrographic profiles, and regional climate indices are used to identify the influence of climate variability on the generation of anomalous turbid river plumes. The evolution of salinity at a coastal station on the 90m isobath between the Itata and Biobío Rivers shows a freshwater surface layer with salinity <32.5 and 5–10m thick during major plume events in 2002, 2005 and 2006. Surface salinity minima are correlated with peaks in turbidy from the normalized water leaving radiance at 555nm (nLw(555)), both representing turbid river plumes. EOF analysis reveals that major turbid plume events occurred primarily during warm phases of the ENSO and PDO, and negative phases of the AAO, when storm tracks are further north. Anomalously large turbid plumes extend long distances offshore (∼70–80km), and individual plumes coalesce into a continuous plume along the coast that covers the entire continental shelf. Season-specific correlation analyses reveal an increased influence of the AAO on river plumes south of Punta Lavapié in spring-summer (negative correlation). North of this major cape, ENSO and PDO indices have a dominant influence on plumes with positive correlations with the nLw(555) signal in winter (and negative in summer). We discuss the biogeochemical implications of plume events and the importance of long-term and high-resolution ocean color observations for studying the temporal evolution of river plumes.

Analysis of spatio‐temporal changes in annual and seasonal precipitation variability in South America‐Chile and related ocean–atmosphere circulation patterns

ABSTRACTEstablishing relationships between coupled ocean–atmospheric patterns and precipitation accumulation is important to describe and predict spatio‐temporal variability on annual or seasonal scales, and also to evaluate how this variability is influenced by global warming. The objective of this study was to examine the leading modes of interannual and seasonal (summer, autumn, winter, and spring) precipitation variability in South America‐Chile, and their significant relationship to seasonally aggregated gridded data and climatic indices. Applying exhaustive data quality control measures to data from 238 rain gauges with different lengths of records between 1893 and 2013, a new data set was created with the objective of obtaining reliable records for further analysis. A comprehensive analysis through empirical orthogonal functions (EOF) allowed for determination of the leading modes of annual and seasonal precipitation and their main spatial patterns for the whole country. The percentage of explained variance in the relationship between seasonally aggregated indices and the leading modes of precipitation confirmed that most of the interannual and winter precipitation variability in Chile is linked to the seasonal aggregation of El Nino Southern Oscillation (ENSO). The leading modes of summer, autumn, and spring precipitation were mostly linked to seasonal aggregations of the Madden and Julian Oscillation (MJO), and the Antarctic Oscillation (AAO).

Relationships between climate variability and radial growth of Nothofagus pumilio near altitudinal treeline in the Andes of northern Patagonia, Chile

Global warming is expected to enhance radial tree growth at alpine treeline sites worldwide. We developed a well-replicated tree-ring chronology from Nothofagus pumilio near treeline in a high precipitation climate on Choshuenco Volcano (40°S) in Chile to examine: (a) variation in tree radial growth in relation to interannual climatic variability; and (b) relationships of radial growth to variability in El Niño Southern Oscillation (ENSO) and the Antarctic Oscillation (AAO) at interannual and decadal time scales. A tree-ring chronology based on 99 tree-ring series from 80 N. pumilio trees near treeline showed a high series intercorrelation (0.48) indicating a strong common environmental signal. Radial growth is negatively correlated with precipitation in late spring (November–December). Temperature and tree growth are positively correlated during late spring and early summer (November–January). Interannual variability in both seasonal climate and in tree growth is strongly teleconnected to ENSO and AAO variability. Radial growth of N. pumilio in this humid high-elevation forest does not show a positive trend over the past half century as predicted from global treeline theory and broadscale warming in the Patagonian-Andean region. Instead, tree growth increased sharply from the 1960s to a peak in the early 1980s but subsequently declined for c. 30years to its lowest level in >100years. The shift to higher radial growth after c. 1976 coincides with a shift towards warmer sea surface temperatures in the tropical Pacific which in turn are associated with warmer growing season temperatures. The decline in tree growth since the mid-1990s is coincident with the increasingly positive phase of the AAO and high spring precipitation periods associated with El Niño conditions. The recent shift towards reduced growth of N. pumilio at this humid high-elevation site coincident with rising AAO mirrors the reduced tree growth beginning in the 1960s for trees growing in relatively xeric, lower elevation sites throughout the Patagonian-Andean region. The current study indicates that N. pumilio growth response in humid high-elevation environments to recent broad-scale warming has been non-linear, and that AAO and ENSO are key climatic forcings of tree growth variability.

地球动力学扁率与南极涛动年际变化的小波相干分析

Variations in the Earths dynamic oblateness ( J 2) reflect large-scale interactions and dynamic changes in global layers. Previous research on the correlation between 4-6 year variations in J 2 and changes in global atmosphere, marine activity, and surface water, indicates that dominant interannual signals in J 2 arise from latitudes higher than 75°, and that variations in J 2 may be related to the ENSO (EI Nino-Southern Oscillation) phenomenon. This study, for the first time, uses a cross wavelet and wavelet coherence method to analyze the correlation between interannual variability in J 2 and the Antarctic Oscillation Index (AAOI)/Southern Oscillation Index (SOI), representing the ENSO phenomenon. The results demonstrate a strong correlation between J 2 signals and the Antarctic Oscillation (AAO) at 4-6 year time scales during 1986-2010 (correlation coefficient larger than 0.8), and show that J 2 signals lag the AAO by about 0-5 months. However, there is no significant or better correlation between variability in J 2 and other SOI signals over the same time period and scales, which may be related to differences in large scale air movement and its spatial distribution characteristics, that are reflected by the AAO and the SOI, respectively.

Modulation of Aleutian Low and Antarctic Oscillation co-variability by ENSO

We use both the National Centers for Environmental Prediction (NCEP)–National Center for Atmospheric Research (NCAR) reanalysis data (1979–2013) and the Community Atmospheric Model Version 3 to explore the modulation of El Nino–Southern Oscillation (ENSO) on the co-variability of the Aleutian Low (AL) and the Antarctic Oscillation (AAO). The empirical orthogonal function analysis on the NCEP–NCAR reanalysis data indicates that after the late-1990s the global sea level pressure (SLP) and 300-hPa geopotential height (Z300) in boreal January are characterized by the concurrence of the AL and the negative phase of the AAO (−AAO). Associated with this AL–AAO co-variation is a sea surface temperature anomaly that resembles the ENSO cycle. Further analyses reveal that the interdecadal change in ENSO signal (westward extension and more La Nina events) is responsible for the co-variability of AL and AAO after the late-1990s. Correspondingly, the El Nino-related anomalous heating and upward motion over the eastern–central equatorial Pacific can lead to the upper-tropospheric divergence in the western–central Pacific. This upper-tropospheric divergence plays an essential role in coupling the equatorial heat anomalies with the variation of the subtropical westerly jet of both hemispheres, and therefore results in the enhanced meridional circulation of the three cells. It thus implies that ENSO might act as a bridge linking AL and AAO after the late-1990s, causing their consistent co-variability. The numerical experiment also supports this hypothesis.

The relationship between the El Niño/La Niña cycle and the transition chains of four atmospheric oscillations. Part II: The relationship and a new approach to the prediction of El Niño

The authors explored the connection and transition chains of the Northern Oscillation (NO) and the North Pacific Oscillation (NPO), the Southern Oscillation (SO), and the Antarctic Oscillation (AAO) on the interannual timescale in a companion paper. In this study, the connection between the transition chains of the four oscillations (the NO and NPO, the SO and AAO) and the El Nino/La Nina cycle were examined. It was found that during the transitions of the four oscillations, alternate anticyclonic/cyclonic correlation centers propagated from the Western Pacific to the Eastern Pacific along both sides of the equator. Between the anticyclonic/cyclonic correlation centers, the zonal wind anomalies also moved eastwardly, favoring the advection of sea surface temperature anomalies from the tropical Western Pacific to the Eastern Pacific. When the anticyclonic anomalies arrived in the Eastern Pacific, the positive phase of NO/SO and La Nina were established and vice versa. Thus, in 4–6 years, with an entire transition chain of the four oscillations, an El Nino/La Nina cycle completed. The eastward propagation of the covarying anomalies of the sea level pressure, zonal wind, and sea surface temperature was critical to the transition chains of the four oscillations and the cycle of El Nino/La Nina.

The relationship between the El Niño/La Niña Cycle and the transition chains of four atmospheric oscillations. Part I: The four oscillations

The first leading modes of the interannual variations in low-level circulation over the North and South Pacific are the Northern Oscillation (NO) and Southern Oscillation (SO), which are oscillations in sea level pressure anomalies (SLPAs) between the eastern and western Pacific Ocean. The second leading modes are the North Pacific Oscillation (NPO) and the Antarctic Oscillation (AAO), which reflect oscillations between the subtropics and the high and middle latitudes. The transition chains of these four oscillations were investigated using the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis data. The general pattern of the transition chain between the NO and NPO was from the negative phase of the NO (NO−) to the positive phase of the NPO (NPO+), then from NO+ to NPO− to NO−. The whole transition chain took about 4–6 years. The general pattern and period of the transition between the SO and AAO were similar to those between the NO and NPO. In addition, the transition chains between the NO and NPO, and the SO and AAO, were almost simultaneous. The transition chains of the four oscillations were found to be closely connected, with the eastward propagations of SLPAs occurring along both sides of the Equator.

Interaction between the MJO and Polar Circulations

Abstract A tropical–polar connection and its seasonal dependence are examined using the real-time multivariate Madden–Julian oscillation (MJO) (RMM) index and daily indices for the annular modes, the Arctic Oscillation (AO) and the Antarctic Oscillation (AAO). On the intraseasonal time scale, the MJO appears to force the annular modes in both hemispheres. On this scale, during the cold season, the convection in the Indian Ocean precedes the increase of the AO/AAO. Interestingly, during the boreal winter (Southern Hemisphere warm season), strong MJOs in the Indian Ocean are related to a decrease of the AAO index, and AO/AAO tendencies are out of phase. On the longer time scales, a persistent AO/AAO anomaly appears to influence the convection in the tropical belt and impact the distribution of MJO-preferred phases. It is shown that this may be a result of the sea surface temperature (SST) changes related to a persistent AO, with cooling over the Indian Ocean and warming over Indonesia. In the Southern Hemisphere, the SST anomalies are to some extent also related to a persistent AAO pattern, but this relationship is much weaker and appears only during the Southern Hemisphere cold season. On the basis of these results, a mechanism involving the air–sea interaction in the tropics is suggested as a possible link between persistent AO and convective activity in the Indian Ocean and western Pacific.

Trends and ENSO/AAO Driven Variability in NDVI Derived Productivity and Phenology alongside the Andes Mountains

Increasing water use and droughts, along with climate variability and land use change, have seriously altered vegetation growth patterns and ecosystem response in several regions alongside the Andes Mountains. Thirty years of the new generation biweekly normalized difference vegetation index (NDVI3g) time series data show significant land cover specific trends and variability in annual productivity and land surface phenological response. Productivity is represented by the growing season mean NDVI values (July to June). Arid and semi-arid and sub humid vegetation types (Atacama desert, Chaco and Patagonia) across Argentina, northern Chile, northwest Uruguay and southeast Bolivia show negative trends in productivity, while some temperate forest and agricultural areas in Chile and sub humid and humid areas in Brazil, Bolivia and Peru show positive trends in productivity. The start (SOS) and length (LOS) of the growing season results show large variability and regional hot spots where later SOS often coincides with reduced productivity. A longer growing season is generally found for some locations in the south of Chile (sub-antarctic forest) and Argentina (Patagonia steppe), while central Argentina (Pampa-mixed grasslands and agriculture) has a shorter LOS. Some of the areas have significant shifts in SOS and LOS of one to several months. The seasonal Multivariate ENSO Indicator (MEI) and the Antarctic Oscillation (AAO) index have a significant impact on vegetation productivity and phenology in southeastern and northeastern Argentina (Patagonia and Pampa), central and southern Chile (mixed shrubland, temperate and sub-antarctic forest), and Paraguay (Chaco).

Ecological and climatic controls of modern wildfire activity patterns across southwestern South America

Understanding how patterns of wildfire activity across biomes are shaped by heterogeneity in biomass resources to burn and atmospheric conditions conducive to burning is a high research priority in the context of global environmental change. Along a latitudinal gradient (25 to 56° S) from semi‐arid scrublands through Mediterranean‐type vegetation to wet forests in southwestern South America (SSA) we analyzed influences of mean climate and interannual climate variability on fire activity using documentary fire records from 1984 to 2008. We identified large regions with common temporal variability in annual area burned, related this variability to local interannual climate variability and in turn to modes of the major tropical and extratropical climate drivers of the southern hemisphere—El Niño‐Southern Oscillation (ENSO) and the Antarctic Oscillation (AAO). Differences in fire activity response to interannual climate variability were related to the relative influences of available biomass to burn, and to weather effects on amounts of fine fuels and fuel moisture conditions. The pattern of average fire activity along this latitudinal moisture/productivity gradient corresponds well with the varying constraints model. This model predicts low fire activity towards the arid extreme due to reduced burnable biomass and again towards the humid extreme due to infrequent weather suitable for drying fuels, and predicts a broad zone of high fire activity at intermediate locations where resources to burn are abundant in all years and fuel moisture dries under reliably dry summer conditions. The dominant influence on interannual climate variability is AAO, which explained most of the variability in fire activity both by reducing seasonal precipitation in mesic and wet forests where fire is dependent on infrequent drought and by enhancing fine fuel production in Mediterranean‐type vegetation where fuel amount and continuity constrain fire activity. In the context of the drying and warming trends in SSA related to the continued positive anomaly in AAO, our results underscore the importance of the varying constraints on fire activity and modulation of fire‐climate relationships by different vegetation types, which is a much needed step toward developing fire projections under future climate.

Propagation of planetary-scale zonal mean wind anomalies and polar oscillations

Global atmospheric variables can be physically decomposed into four components: (1) the zonal time averaged climate symmetric component, (2) the time averaged climate asymmetric, (3) the zonal-mean transient symmetric anomaly, and (4) the transient asymmetric anomaly. This study analyzes the relationships between the intra-seasonal and inter-annual variability of planetary scale decomposed zonal and meridional winds in the tropopause, and oscillations such as those from the El Nino-Southern Oscillation (ENSO), the Arctic Oscillation (AO) and the Antarctic Oscillation (AAO). The tropical inter-annual zonal mean wind anomalies in the tropopause are linked with the ENSO cycle and can propagate into the subtropics, mid-latitudes, and polar front regions via abnormal meridional vertical cells. Similarly, tropical intra-seasonal (40–60-d) zonal wind anomalies can reach the subtropics and mid-latitudes. The polar intra-seasonal zonal wind anomalies in the tropopause can propagate toward high-latitude areas. Thus, the AO and the AAO are the result of the interaction and propagation of these planetary scale zonal wind anomalies.

Southern Patagonia’s Perito Moreno Glacier, Lake Argentino, and Santa Cruz River hydrological system: An overview

► The hydrology of Patagonia’s Moreno Glacier system suggests the influence of ENSO and AAO over the snout dynamics. ► The incidence of interannual climatic anomalies appears embedded in decadal or quasi bidecadal damming periods. ► There is no significant trend in the Santa Cruz River’s discharge with the exception of the southern spring melt periods. ► The glacier’s stability looks like a complex multivariate process and we do not rule out the occasional role of ENSO/AAO. An overview of the hydrological data from Patagonia’s Perito Moreno Glacier–Lake Argentino- and Santa Cruz River system reinforces our previous assertion that the El Niño Southern Oscillation (ENSO) and the Antarctic Oscillation (AAO) are teleconnected with the rupture sequence when the glacier’s snout harmonically dams (during certain interannual periods) the Rico branch of Lake Argentino. It is clear, however, that the incidence of interannual climatic anomalies is not uniform in time and appears embedded in decadal or quasi bidecadal periods of relative damming inactivity. The use of nonparametric tests shows that there are no significant positive trends in the river’s annual discharge with the only exception of the yearly snowmelt/ice melt periods (September–October), when riverine flow appears to increase with statistical significance. The question of the glacier’s stability looks like a complex multivariate process, although we do not rule out the occasional role of ENSO/AAO. A longer hydrological data series (i.e., 100 years) would prove useful in casting some light on this intriguing process, surely accounting for the glacier’s response time.

The relationship between the canonical ENSO and the phase transition of the Antarctic oscillation at the quasi-quadrennial timescale

A correlation analysis is performed to investigate the relationship between El Nino-Southern Oscillation (ENSO) and the Antarctic oscillation (AAO) at the quasi-quadrennial (QQ) timescale. It is found that the cold tongue index (CTI) and the AAO index (AAOI) are negatively correlated with about a 7-month lead-time, while they are positively correlated with about a 15-month lag-time. To further explore this relationship, complex empirical orthogonal function analysis is employed in the QQ sea level pressure (SLP) anomalies from 1951 to 2002. The results indicate that, during the ENSO cycle, there exists one kind of global tropical wave of wavenumber 1 (GTW1) propagating eastward. With the traveling of GTW1, the tropical SLP anomaly tends to intrude into the southern mid-latitudes. Accordingly, three strong signals travel synchronously along the circum-South-Pacific path, and a relatively weak signal extends eastward and poleward over the South Ocean in the Atlantic-Indian Ocean sector. Following the propagation of these signals, the AAO phase tends to be reversed progressively. As a result, there exists an evident lead-lag correlation between CTI and AAOI. It can be concluded that ENSO plays a key role in the phase transition of AAO at the QQ timescale. It is also noticed that this regular relationship is only evident in the canonical ENSO events, for which sea surface temperature (SST) anomalies extend westward from the tropical eastern Pacific. On the other hand, the similar relationships are not found among those atypical ENSO events for which SST anomalies spread eastward from the central Pacific, such as the 1982–1983 ENSO event.