Southern Hemisphere Atmospheric Circulation Research Articles

Abrupt ice-age shifts in southern westerly winds and Antarctic climate forced from the north.

The mid-latitude westerly winds of the Southern Hemisphere play a central role in the global climate system via Southern Ocean upwelling1, carbon exchange with the deep ocean2, Agulhas leakage (transport of Indian Ocean waters into the Atlantic)3 and possibly Antarctic ice-sheet stability4. Meridional shifts of the Southern Hemisphere westerly winds have been hypothesized to occur5,6 in parallel with the well-documented shifts of the intertropical convergence zone7 in response to Dansgaard-Oeschger (DO) events- abrupt North Atlantic climate change events of the last ice age. Shifting moisture pathways to West Antarctica8 are consistent with this view but may represent a Pacific teleconnection pattern forced from the tropics9. The full response of the Southern Hemisphere atmospheric circulation to the DO cycle and its impact on Antarctic temperature remain unclear10. Here we use five ice cores synchronized via volcanic markers to show that the Antarctic temperature response to the DO cycle can be understood as the superposition of two modes: a spatially homogeneous oceanic 'bipolar seesaw' mode that lags behind Northern Hemisphere climate by about 200 years, and a spatially heterogeneous atmospheric mode that is synchronous with abrupt events in the Northern Hemisphere. Temperature anomalies of the atmospheric mode are similar to those associated with present-day Southern Annular Mode variability, rather than the Pacific-South American pattern. Moreover, deuterium-excess records suggest a zonally coherent migration of the Southern Hemisphere westerly winds over all ocean basins in phase with Northern Hemisphere climate. Our work provides a simple conceptual framework for understanding circum-Antarctic temperature variations forced by abrupt Northern Hemisphere climate change. We provide observational evidence of abrupt shifts in the Southern Hemisphere westerly winds, which have previously documented1-3 ramifications for global ocean circulation and atmospheric carbon dioxide. These coupled changes highlight the necessity of a global, rather than a purely North Atlantic, perspective on the DO cycle.

Intense Winter Surface Melt on an Antarctic Ice Shelf

AbstractThe occurrence of surface melt in Antarctica has hitherto been associated with the austral summer season, when the dominant source of melt energy is provided by solar radiation. We use in situ and satellite observations from a previously unsurveyed region to show that events of intense surface melt on Larsen C Ice Shelf occur frequently throughout the dark Antarctic winter, with peak intensities sometimes exceeding summertime values. A regional atmospheric model confirms that in the absence of solar radiation, these multiday melt events are driven by outbreaks of warm and dry föhn wind descending down the leeside of the Antarctic Peninsula mountain range, resulting in downward turbulent fluxes of sensible heat that drive sustained surface melt fluxes in excess of 200 W/m2. From 2015 to 2017 (including the extreme melt winter of 2016), ∼23% of the annual melt flux was produced in winter, and spaceborne observations of surface melt since 2000 show that wintertime melt is widespread in some years. Winter melt heats the firn layer to the melting point up to a depth of ∼3 m, thereby facilitating the formation of impenetrable ice layers and retarding or reversing autumn and winter cooling of the firn. While the absence of a trend in winter melt is consistent with insignificant changes in the observed Southern Hemisphere atmospheric circulation during winter, we anticipate an increase in winter melt as a response to increasing greenhouse gas concentration.

Evaluation of ocean-atmospheric indices as predictors for summer streamflow of the Yangtze River based on ROC analysis

Antecedent anomalies of sea surface temperature and atmospheric circulation are important signals for making long-term streamflow forecasts. In this study, four groups of ocean-atmospheric indices, i.e, El Nino Southern Oscillation (ENSO), the Northern Hemisphere atmospheric circulation, the Southern Hemisphere atmospheric circulation (SAC), and the Western Pacific and Indian Ocean SST (WPI), are evaluated for forecasting summer streamflow of the Yangtze River. The gradient boosting regression tree (GBRT) is used to forecast streamflow based on each group of indices. The score based on receiver operating characteristics (ROC) curves, i.e., area under the ROC curve (AUC), is used to evaluate skills of models for identifying the high category and the low category of summer streamflow. It is found that the ENSO group and the SAC group show higher AUC values. Furthermore, both AUC values of GBRT models and individual indices show that the low flow years are easier to be identified than the high flow years. The result of this study highlights the skill from the Southern Hemisphere circulation systems for forecasting summer streamflow of the Yangtze River. Results of relative influences of predictors in GBRT models and AUC of individual indices indicate some key ocean-atmospheric indices, such as the Multivariate ENSO Index and the 500-hPa height of the east of Australia.

Effect of Gravity Waves From Small Islands in the Southern Ocean on the Southern Hemisphere Atmospheric Circulation

AbstractThe effect of small islands in the Southern Ocean on the atmospheric circulation in the Southern Hemisphere is considered with a series of simulations using the NASA Goddard Earth Observing System Chemistry‐Climate Model in which the gravity wave stress generated by these islands is increased to resemble observed values. The enhanced gravity wave drag leads to a 2 K warming of the springtime polar stratosphere, partially ameliorating biases in this region. Resolved wave drag declines in the stratospheric region in which the added orographic gravity waves deposit their momentum, such that changes in gravity waves are partially compensated by changes in resolved waves, though resolved wave drag increases further poleward. The orographic drag from these islands has impacts for surface climate, as biases in tropospheric jet position are also partially ameliorated. These results suggest that these small islands are likely contributing to the missing drag near 60°S in the upper stratosphere evident in many data assimilation products.

Seasonal climate summary for the southern hemisphere (winter 2016): a strong negative Indian Ocean Dipole brings wet conditions to Australia

This is a summary of the southern hemisphere atmospheric circulation patterns and meteorological indices for winter 2016; an account of seasonal rainfall and temperature for the Australian region and the broader southern hemisphere is also provided. One of the strongest negative phases on record of the Indian Ocean Dipole (IOD) developed during the season, contributing to Australia's second wettest winter on record, with rainfall above average over the vast majority of the continent. Neutral conditions prevailed in the tropical Pacific following the end of a strong El Niño event in autumn 2016, but the continuing effect of the 2015-16 El Niño was still evident in southern hemisphere temperatures, which were at or near record high levels.

Seasonal climate summary for the southern hemisphere (autumn 2016): El Niño slips into neutral and a negative Indian Ocean Dipole develops

This is a summary of the southern hemisphere atmospheric circulation patterns and meteorological indices for autumn 2016; an account of seasonal rainfall and temperature for the Australian region is also provided. While autumn began with a weak El Niño signal in the Pacific, the decay of the El Niño was evident with subsurface temperatures in the central and eastern Pacific continuing to cool. Later in the season, the Indian Ocean Dipole (IOD) transitioned to a negative phase. The negative IOD combined with warm water to Australia’s north channeled warm, moisture-laden air over the continent; unseasonable rainfall ensued, over eastern and northern Australia and New Zealand’s western coastal areas during May.Temperatures averaged over the southern hemisphere were record warm for autumn, both for land and ocean areas; separately or combined. For Australia, autumn arrived during a significant and prolonged heatwave that contributed to the warmest autumn on record for Australia.The elevated sea surface temperatures (SSTs) recorded in the Australian region earlier in the year persisted, and were warmest on record for autumn. Warm SSTs led to a global coral bleaching event affecting reefs in tropical waters; while, in extra-tropical waters, diminished kelp forests were observed. In the Australian region, reefs off the northwestern coast and, in northern areas of the Great Barrier Reef, were bleached. The most severe marine heatwave since records began was recorded in the Great Barrier Reef lagoon.

The Signature of Southern Hemisphere Atmospheric Circulation Patterns in Antarctic Precipitation.

We provide the first comprehensive analysis of the relationships between large‐scale patterns of Southern Hemisphere climate variability and the detailed structure of Antarctic precipitation. We examine linkages between the high spatial resolution precipitation from a regional atmospheric model and four patterns of large‐scale Southern Hemisphere climate variability: the southern baroclinic annular mode, the southern annular mode, and the two Pacific‐South American teleconnection patterns. Variations in all four patterns influence the spatial configuration of precipitation over Antarctica, consistent with their signatures in high‐latitude meridional moisture fluxes. They impact not only the mean but also the incidence of extreme precipitation events. Current coupled‐climate models are able to reproduce all four patterns of atmospheric variability but struggle to correctly replicate their regional impacts on Antarctic climate. Thus, linking these patterns directly to Antarctic precipitation variability may allow a better estimate of future changes in precipitation than using model output alone.

Pollen-based temperature and precipitation records of the past 14,600 years in northern New Zealand (37°S) and their linkages with the Southern Hemisphere atmospheric circulation

Regional vegetation, climate history, and local water table fluctuations for the past 14,600 years are reconstructed from pollen and charcoal records of an ombrogenous peatbog in northern New Zealand (38°S). A long-term warming trend between 14,600 and 10,000 cal. yr BP is punctuated by two brief plateaux between 14,200–13,800 and 13,500–12,000 cal. yr BP. Periods of relatively drier conditions are inferred between 14,000–13,400 and 12,000–10,000 cal. yr BP, while a long-term wet period is observed between 10,000 and 6000 cal. yr BP. The last 7000 years feature relatively stable temperatures, a long-term drying trend that culminates with persistent drier conditions over the last 3000 years and cyclical fluctuations in the bog’s water table and fires. Present-day climate controls and comparisons with other climate reconstructions from New Zealand, the Southern Hemisphere mid-latitudes and the tropical Pacific suggest that complex and temporally variable teleconnections exist between northern New Zealand and the Southern Hemisphere low- and high-latitude circulation.

Glacial/interglacial changes of Southern Hemisphere wind circulation from the geochemistry of South American dust

The latitudinal displacement of the southern westerlies and associated climate systems is a key parameter for understanding the variations of Southern Hemisphere atmospheric circulation during the Late Quaternary Period. To increase understanding of past atmospheric circulation and of the paleo-environmental conditions associated with continental dust sources, we dig deeper into dust provenance in paleo-archives of the Southern Hemisphere. We present here a Sr–Nd isotopic and rare earth element study of surface sediments collected along a ∼4000 km latitudinal band from arid and semi-arid terrains in southern South America. Findings from terrains that served as paleo-dust suppliers are compared with modern dust collected from monitoring stations along the same latitudinal band, which affords a test on how actual present-day aeolian compositions compare to those of the past potential source areas. Moreover, the comparison between past and present-day datasets is useful for understanding present-day atmospheric circulation.Armed with a new comprehensive dataset, we revise previous interpretations of the provenance of dust trapped in the Antarctic ice and sediments deposited in the South Atlantic sector of the Southern Ocean. These comparisons support multiple source regions in southern South America that changed with climates. The findings reveal that, although Patagonia plays an important role in contributing dust to the higher latitudes, central Western Argentina and (to a lesser extent) the southern Puna region also emerge as potentially important dust sources during glacial times. The southern Altiplano appears to be a major contributor during interglacial periods as well. We rely in part on an understanding of modern wind–dust activities to conclude that the possible presence of southern South America source regions – other than Patagonia – in East Antarctic ice is consistent with an overall equatorward displacement during glacial times of both the mid-latitude westerlies and the subtropical jet stream.

Changes in El Niño – Southern Oscillation (ENSO) conditions during the Greenland Stadial 1 (GS-1) chronozone revealed by New Zealand tree-rings

The warming trend at the end of the last glacial was disrupted by rapid cooling clearly identified in Greenland (Greenland Stadial 1 or GS-1) and Europe (Younger Dryas Stadial or YD). This reversal to glacial-like conditions is one of the best known examples of abrupt change but the exact timing and global spatial extent remain uncertain. Whilst the wider Atlantic region has a network of high-resolution proxy records spanning GS-1, the Pacific Ocean suffers from a scarcity of sub-decadally resolved sequences. Here we report the results from an investigation into a tree-ring chronology from northern New Zealand aimed at addressing the paucity of data. The conifer tree species kauri (Agathis australis) is known from contemporary studies to be sensitive to regional climate changes. An analysis of a ‘historic’ 452-year kauri chronology confirms a tropical-Pacific teleconnection via the El Nino – Southern Oscillation (ENSO). We then focus our study on a 1010-year sub-fossil kauri chronology that has been precisely dated by comprehensive radiocarbon dating and contains a striking ring-width downturn between ∼12,500 and 12,380 cal BP within GS-1. Wavelet analysis shows a marked increase in ENSO-like periodicities occurring after the downturn event. Comparison to low- and mid-latitude Pacific records suggests a coherency with ENSO and Southern Hemisphere atmospheric circulation change during this period. The driver(s) for this climate event remain unclear but may be related to solar changes that subsequently led to establishment and/or increased expression of ENSO across the mid-latitudes of the Pacific, seemingly independent of the Atlantic and polar regions.

Projections of Southern Hemisphere atmospheric circulation interannual variability

An analysis is made of the coherent patterns, or modes, of interannual variability of Southern Hemisphere 500 hPa geopotential height field under current and projected climate change scenarios. Using three separate multi-model ensembles (MMEs) of coupled model intercomparison project phase 5 (CMIP5) models, the interannual variability of the seasonal mean is separated into components related to (1) intraseasonal processes; (2) slowly-varying internal dynamics; and (3) the slowly-varying response to external changes in radiative forcing. In the CMIP5 RCP8.5 and RCP4.5 experiments, there is very little change in the twenty-first century in the intraseasonal component modes, related to the Southern annular mode (SAM) and mid-latitude wave processes. The leading three slowly-varying internal component modes are related to SAM, the El Nino–Southern oscillation (ENSO), and the South Pacific wave (SPW). Structural changes in the slow-internal SAM and ENSO modes do not exceed a qualitative estimate of the spatial sampling error, but there is a consistent increase in the ENSO-related variance. Changes in the SPW mode exceed the sampling error threshold, but cannot be further attributed. Changes in the dominant slowly-varying external mode are related to projected changes in radiative forcing. They reflect thermal expansion of the tropical troposphere and associated changes in the Hadley Cell circulation. Changes in the externally-forced associated variance in the RCP8.5 experiment are an order of magnitude greater than for the internal components, indicating that the SH seasonal mean circulation will be even more dominated by a SAM-like annular structure. Across the three MMEs, there is convergence in the projected response in the slow-external component.

Ideas and perspectives: Southwestern tropical Atlantic coral growth response to atmospheric circulation changes induced by ozone depletion in Antarctica

Abstract. Recent Southern Hemisphere (SH) atmospheric circulation, predominantly driven by stratospheric ozone depletion over Antarctica, has caused changes in climate across the extratropics. Here, we present evidence that the Brazilian coast (southwestern Atlantic) may have been impacted from both wind and sea-surface temperature changes derived from this process. Skeleton analysis of massive coral species living in shallow waters off Brazil are very sensitive to air–sea interactions, and seem to record this impact. Growth rates of Brazilian corals show a trend reversal that fits the ozone depletion evolution, confirming that ozone impacts are far reaching and potentially affect coastal ecosystems in tropical environments.

The signatures of large‐scale patterns of atmospheric variability in Antarctic surface temperatures

AbstractWe investigate the impact that the four principal large‐scale patterns of Southern Hemisphere (SH) atmospheric circulation variability have on Antarctic surface air temperature (SAT): (1) the southern baroclinic annular mode (BAM), which is associated with variations in extratropical storm amplitude; (2) the Southern Annular Mode (SAM), associated with latitudinal shifts in the midlatitude jet; and (3) the two Pacific‐South American patterns (PSA1 and PSA2), which are characterized by wave trains originating in the tropical Pacific that extend across the SH extratropics. A key aspect is the use of 35 years of daily observations and reanalysis data, which affords a sufficiently large sample size to assess the signatures of the circulation patterns in both the mean and variability of daily mean SAT anomalies. The BAM exerts the weakest influence on Antarctic SAT, albeit it is still important over select regions. Consistent with previous studies, the SAM is shown to influence SAT across most of the continent throughout the year. The PSA1 also affects SAT across almost all of Antarctica. Regionally, both PSA patterns can exert a greater impact on SAT than the SAM but also have a significantly weaker influence during summer, reflecting the seasonality of the SH response to El Niño–Southern Oscillation. The SAM and PSA patterns have distinct signatures in daily SAT variance that are physically consistent with their signatures in extratropical dynamic variability. The broad‐scale climate linkages identified here provide benchmarks for interpreting the Antarctic climate response to future changes in tropical sea surface temperatures, ozone recovery, and greenhouse gas increases.

A Linkage Observed between Austral Autumn Antarctic Oscillation and Preceding Southern Ocean SST Anomalies

Abstract In this study, the authors apply a lagged maximum covariance analysis (MCA) to capture the cross-seasonal coupled patterns between the Southern Ocean sea surface temperature (SOSST) and extratropical 500-hPa geopotential height anomalies in the Southern Hemisphere, from which Niño-3.4 signals and their linear trends are removed to a certain extent. Statistically significant results show that the dominant feature of ocean–atmosphere interaction is likely the effect of atmosphere on SOSST anomalies, with a peak occurring when the atmosphere leads the SOSST by 1 month. However, the most eye-capturing phenomenon is that the austral autumn atmospheric signal, characterized by a negatively polarized Antarctic Oscillation (AAO), is significantly related to the gradual evolution of preceding SOSST anomalies, suggesting that the SOSST anomalies tend to exert an effect on the Southern Hemisphere atmospheric circulation. A regression analysis based on SOSST anomaly centers confirms these features. It is also demonstrated that the gradual evolution of changes in SOSST is mainly driven by internal atmospheric variability via surface turbulent heat flux associated with cold or warm advection and that the atmospheric circulation experiences a change from a typical positive AAO to a negative phase in this process. These findings indicate that such a long lead cross-seasonal covariance could contribute to a successful prediction of AAO-related atmospheric circulation in austral autumn from the perspective of SOSST anomalies, with lead times up to 6–7 months.

Systematic attribution of observed Southern Hemisphere circulation trends to external forcing and internal variability

Abstract. A critical question in the global warming debate concerns the causes of the observed trends of the Southern Hemisphere (SH) atmospheric circulation over recent decades. Secular trends have been identified in the frequency of occurrence of circulation regimes, namely the positive phase of the Southern Annular Mode (SAM) and the hemispheric wave-3 pattern which is associated with blocking. Previous studies into the causes of these secular trends have either been purely model based, have not included observational forcing data or have mixed external forcing with indices of internal climate variability impeding a systematic and unbiased attribution of the causes of the secular trends. Most model studies also focused mainly on the austral summer season. However, the changes to the storm tracks have occurred in all seasons and particularly in the austral winter and early spring when midlatitude blocking is most active and stratospheric ozone should not play a role. Here we systematically attribute the secular trends over the recent decades using a non-stationary clustering method applied to both reanalysis and observational forcing data from all seasons. While most previous studies emphasized the importance of stratospheric ozone depletion in causing austral summer SH circulation trends, we show observational evidence that anthropogenic greenhouse gas concentrations have been the major driver of these secular trends in the SAM and blocking when all seasons are considered. Our results suggest that the recovery of the ozone hole might delay the signal of global warming less strongly than previously thought and that effects from all seasons are likely crucial in understanding the causes of the secular trends.

A Decadal-Scale Teleconnection between the North Atlantic Oscillation and Subtropical Eastern Australian Rainfall

Abstract The time series of twentieth-century subtropical eastern Australian rainfall (SEAR) shows evident fluctuations over decadal to multidecadal time scales. Using observations from the period 1900–2013, it was found that SEAR is connected to the North Atlantic Oscillation (NAO) over decadal time scales, with the NAO leading by around 15 yr. The physical mechanism underlying this relationship was investigated. The NAO can have a delayed impact on sea surface temperature (SST) fluctuations in the subpolar Southern Ocean (SO), and these SST changes could in turn contribute to the decadal variability in SEAR through their impacts on the Southern Hemisphere atmospheric circulation. This observed lead of the NAO relative to SO SST and the interhemispheric SST seesaw mechanism are reasonably reproduced in a long-term control simulation of an ocean–atmosphere coupled model. The NAO exerts a delayed effect on the variation of Atlantic meridional overturning circulation that further induces seesaw SST anomalies in the subpolar North Atlantic and SO. With evidence that the NAO precedes SEAR decadal variability via a delayed SO bridge, a linear model for SEAR decadal variability was developed by combination of the NAO and Pacific decadal oscillation (PDO). The observed SEAR decadal variability is considerably well simulated by the linear model, and the relationship between the simulation and observation is stable. SEAR over the coming decade may increase slightly, because of the recent NAO weakening and the return of negative PDO phase.

Teleconnections between Tropical Pacific SST Anomalies and Extratropical Southern Hemisphere Climate

Abstract Teleconnections from tropical Pacific sea surface temperature (SST) anomalies to the high-latitude Southern Hemisphere (SH) are examined using observations and reanalysis. Analysis of tropical Pacific SST anomalies is conducted separately for the central Pacific (CP) and eastern Pacific (EP) regions. During the austral cold season, extratropical SH atmospheric Rossby wave train patterns are observed in association with both EP and CP SST variability. The primary difference between the patterns is the westward displacement of the CP-related atmospheric anomalies, consistent with the westward elongation of CP-related convective SST required for upper-level divergence and Rossby wave generation. Consequently, CP-related patterns of SH SST, Antarctic sea ice, and temperature anomalies also exhibit a westward displacement, but otherwise, the cold season extratropical SH teleconnections are largely similar. During the warm season, however, extratropical SH teleconnections associated with tropical CP and EP SST anomalies differ substantially. EP SST variability is linked to largely zonally symmetric structures in the extratropical atmospheric circulation, which projects onto the southern annular mode (SAM), and is strongly related to the SH temperature and sea ice fields. In contrast, CP SST variability is only weakly related to the SH atmospheric circulation, temperature, or sea ice fields and no longer exhibits any clear association with the SAM. One hypothesized mechanism suggests that the relatively weak CP-related SST anomalies are not able to substantially impact the background flow of the subtropical jet and its subsequent interaction with equatorward-propagating waves associated with variability in the SAM. However, there is currently no widely established mechanism that links tropical Pacific SST anomalies to the SAM.

Assessment of Modes of Interannual Variability of Southern Hemisphere Atmospheric Circulation in CMIP5 Models

Abstract An assessment is made of the modes of interannual variability in the seasonal mean summer and winter Southern Hemisphere (SH) 500-hPa geopotential height in the twentieth century in models from the Coupled Model Intercomparison Project (CMIP) phase 5 (CMIP5) dataset. Modes of variability of both the slow (signal) and intraseasonal (noise) components in the CMIP5 models are evaluated against those estimated from reanalysis data. There is general improvement in the leading modes of the slow (signal) component in CMIP5 models compared with the CMIP phase 3 (CMIP3) dataset. The largest improvement is in the spatial structures of the modes related to El Niño–Southern Oscillation variability in SH summer. An overall score metric is significantly higher for CMIP5 over CMIP3 in both seasons. The leading modes in the intraseasonal noise component are generally well reproduced in CMIP5 models, and there are few differences from CMIP3. A new total overall score metric is used to rank the CMIP5 models over both seasons. Weighting the seasons by the relative spread of overall scores is shown to be suitable for generating multimodel ensembles for further analysis of interannual variability. In multimodel ensembles, it is found that an ensemble of size 5 or 6 is sufficient in SH summer to reproduce well the dominant modes. In contrast, about 13 models are typically are required in SH winter. It is shown that it is necessary that the selected models individually reproduce well the leading modes of the slow component.

Impacts of two types of El Niño on atmospheric circulation in the Southern Hemisphere

Based on NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis data from 1979 to 2010, the impacts of two types of El Nino on atmospheric circulation in the Southern Hemisphere (SH) are analyzed. It is shown that, when a warming event occurs in the equatorial eastern Pacific (EP El Nino), there is a negative sea level pressure (SLP) anomaly in the eastern Pacific and a positive one in the western Pacific. Besides, there exists a negative anomaly between 40°S and 60°S and a positive anomaly to the south of 60°S. When a warming event in the central Pacific (CP El Nino) occurs, there appears a negative SLP anomaly in the central Pacific and a positive SLP anomaly in the eastern and western Pacific, but the SLP anomalies are not so evident in the SH extratropics. In particular, the Pacific-South America (PSA) pattern induced by the CP El Nino is located more northwestward, with a weaker anomaly compared with the EP El Nino. This difference is directly related with the different position of heating centers associated with the two types of El Nino events. Because the SST anomaly associated with CP El Nino is located more westward than that associated with EP El Nino, the related heating center tends to move westward and the response of SH atmospheric circulation to the tropical heating changes accordingly, thus exciting a different position of the PSA pattern. It is also noted that the local meridional cell plays a role in the SH high latitudes during EP El Nino. The anomalous ascending motion due to the enhancement of convection over the eastern Pacific leads to an enhancement of the local Hadley cell and the meridional cell in the middle and high latitudes, which in turn induces an anomalous descending motion and the related positive anomaly of geopotential height over the Amundsen-Bellingshausen Sea.

Teleconnections and predictive characteristics of Australian seasonal rainfall

A new methodology is proposed that allows patterns of interannual covariability, or teleconnections, between the intraseasonal and slow components of seasonal mean Australian rainfall and the corresponding components in the Southern Hemisphere atmospheric circulation to be estimated. In all seasons, the dominant rainfall–circulation teleconnections in the intraseasonal component are shown to have the characteristic features associated with well-known intraseasonal dynamical and statistical atmospheric modes and their relationship with rainfall. Thus, for example, there are patterns of interannual covariability that reflect rainfall relationships with the intraseasonal Southern Annular Mode, the Madden-Julian Oscillation and wavenumber 3 and 4 intraseasonal modes of variability. The predictive characteristics of the atmospheric circulation–rainfall relationship are shown to reside with the slow components. In all seasons, we find rainfall–circulation teleconnections in the slow components related to the El Nino-Southern Oscillation. Each season also has a coupled mode, with a statistically significant trend in the time series of the atmospheric component that appears to be related to recent observed trends in rainfall. The slow Southern Annular Mode also features in association with southern Australian rainfall, especially during austral winter and spring. There is also evidence of an influence of Indian Ocean sea surface temperature variability on rainfall in southeast Australia during austral winter and spring.