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Climate change has marked effects on global weather patterns and oceanic systems, impacting animal behaviour and fitness in potentially profound ways. Despite this, we lack detailed information about species' responses to climatic variation. Using an 11‐year tracking dataset of over 300 individual birds, we explore the consequences of variation in the southern annular mode (SAM) and southern oscillation index (SOI) for individual behaviour and fitness in wandering albatrosses Diomedea exulans breeding in the Southern Indian Ocean. Our results reveal distinct responses between males and females to climatic variation that align with the impacts of each climatic index on the distinct foraging ranges of each sex. In positive SAM phases, linked to poorer foraging conditions in female ranges and better conditions in male ranges, females exhibited behaviour consistent with reduced foraging success: that is, fewer prey capture attempts and more movement between feeding patches. Males, on the other hand, showed no behavioural change. During positive SOI phases, associated with good foraging conditions in both male and female foraging ranges, both sexes showed evidence of more successful foraging, with birds engaging in more search behaviour, and taking shorter trips with fewer prey capture attempts, together indicating increased food intake per unit time. We found limited evidence for a role of individual variation, as measured through differences in personality, suggesting that plastic responses to climate are sufficiently important so as to obscure inter‐individual variation. Supporting this was the finding that individual breeding success was unaffected by climatic variation, suggesting that plastic foraging behaviour allows albatrosses to mitigate climate impacts and maintain reproductive output. [ABSTRACT FROM AUTHOR]

The current study investigates the modulation of the tropical cyclone (TC) frequency (TCF) over the Bay of Bengal (BoB) by the southern annular mode (SAM). The analysis reveals that the SAM–TCF relationship during October–November–December has undergone interdecadal changes from significant during 1971–1994 to insignificant during 1995–2021. This contrasting influence of the SAM on the TCF occurrence is also echoed in the large‐scale environmental variables conducive to forming tropical cyclones (TCs). Based on the possible mechanism, we found that the SAM can imprint tripole sea surface temperature (SST) patterns in the southern Indian Ocean via altering surface wind speed from 1971 to 1994. The SAM‐related tripole SST pattern induces the surface‐level anticyclone anomaly, which enhances the south easterlies towards the western equatorial Indian Ocean. Such intensified anomalous wind crosses the equator and diverts towards the east to form the cyclone anomaly in the BoB. Meanwhile, at 200 hPa, the anomalous anticyclone over western Australia induces divergent wind flows over the study region. Consequently, the ascending motion in BoB promotes the tropical cyclone generation. During 1995–2021, however, the SAM is associated with the dipole SST pattern in the southern Indian Ocean. Correspondingly, the SAM‐related dipole SST yields anomalous atmospheric circulations confined to the Southern Hemisphere and eventually fails to impact the formation of TCs in the northern Indian Ocean, where the study region is located. The findings of this research can be useful in advancing our knowledge of the interannual variability of TCs activity in the BoB based on the remote climate signal. [ABSTRACT FROM AUTHOR]

The Antarctic vortex of October–December 2020 was the strongest on record in the satellite era for the season in the mid‐ to lower stratosphere. However, it was poorly predicted by the Australian Bureau of Meteorology's operational seasonal climate forecast system of that time, ACCESS‐S1, even at a short lead time of a month. Using the current operational forecast system, ACCESS‐S2, we have, therefore, tried to find a primary cause of the limited predictability of this event and conducted forecast sensitivity experiments to understand the potential role of ozone in the event and its associated anomalies of the Southern Annular Mode (SAM) and rainfall over south–eastern Australia and western Patagonia. Here, we show that the 2020 strong vortex event did not follow the canonical dynamical evolution seen in previous strong vortex events in spring but suddenly appeared as a result of the record‐low upward propagating wave activity in September 2020. The ACCESS‐S2 forecasts significantly underestimated the negative wave forcing in September even at zero lead time, irrespective of the ozone configuration, therefore falling short in predicting the record strength of the polar vortex in late spring 2020. Nevertheless, ACCESS‐S2 with prescribed realistic ozone that had large anomalies in the Antarctic stratosphere significantly better predicted the strong vortex and the subsequent positive SAM and related rainfall anomalies over south–eastern Australia and western Patagonia in the austral summer of 2020–21. This highlights the potentially important role of ozone variations for seasonal climate forecasting as a source of long‐lead predictability. Plain Language Summary: The Antarctic vortex of October–December 2020 was the strongest on record in the satellite observation era for that season when monitored at 60°S in the mid‐ to lower stratosphere (altitudes of 15–30 km). However, this super vortex event was poorly predicted by the Australian Bureau of Meteorology (BoM)'s seasonal climate forecast system even at 1‐month lead time. We argue that the 2020 strong vortex was likely caused by an abrupt reduction in the upward propagating wave activity from the troposphere in September 2020, which left the stratospheric vortex undisturbed and strong. The BoM seasonal forecast system substantially underpredicted the negative wave forcing in September 2020, resulting in a poor forecast performance for the vortex strength in the following season. Forecast experiments prescribed with observed versus climatological ozone concentrations further show that using the observed ozone, characterized by a significant loss over Antarctica in spring 2020, improved the ensemble mean forecasts for the 2020 vortex strength by ∼10%–20% at different levels of the stratosphere and the associated surface climate features such as the poleward shift of the Southern Hemisphere midlatitude jet and anomalously high rainfall over south–eastern Australia and low rainfall over western Patagonia in the following summer. Key Points: The Antarctic vortex of 2020 was the strongest event in the satellite era for the October–December mean in the mid‐ to lower stratosphereSignificant lack of tropospheric wave forcing in September 2020 was responsible for the sudden appearance of the record strong polar vortexImposing realistic ozone concentrations significantly improved forecasts of the 2020 polar vortex strength and its downward impact [ABSTRACT FROM AUTHOR]

Accompanying global warming, Antarctic sea-ice extent shows a somewhat increasing trend from 1979 to 2014, followed by an abrupt decrease after 2016. Our previous study examined the change of Antarctic sea-ice extent in austral summer, autumn and spring. In this study, we turn our attention to the austral winter, relating the main modes of sea-ice variability to sea-ice extent in the Pacific, Atlantic and Indian sectors of the Southern Ocean. We find that the modes with the strongest correlation with the sea-ice extent are the third, first and first modes in the Pacific, Atlantic and Indian sectors, respectively. Atmospheric circulation anomalies of zonal wavenumber three over the Southern Ocean, related to planetary wave trains induced by the SST anomalies over the south-western Pacific and the southern Indian oceans, can explain sea-ice concentration anomalies of the third mode in the Pacific sector through thermodynamic and dynamic processes. Sea-ice anomalies of the first modes in the Atlantic and Indian sectors result from atmospheric circulation anomalies of a positive and negative phases of the Southern Annular Mode, respectively. The anomalous Southern Annular Mode is also associated with wave trains over the Southern Ocean excited by SST anomalies over the southern Indian Ocean and the south-western Pacific Ocean. The relationship between SST anomalies and Antarctic sea-ice anomalies can provide a reference for the prediction of Antarctic sea-ice anomalies in austral winter on interannual and decadal timescales.

Ensemble forecasts have been shown to better predict observed Atlantic climate variability than that of their own ensemble members. This phenomenon—termed the signal‐to‐noise paradox—is found to be widespread across models, timescales, and climate variables, and has wide implications. The signal‐to‐noise paradox can be interpreted as forecasts underestimating the amplitude of predictable signals on seasonal‐to‐decadal timescales. The cause of this remains unknown. Here, we examine sea level pressure variability from a very large multi‐model ensemble of uninitialized atmosphere‐only simulations, focusing on boreal winter. To assess signal‐to‐noise errors, the ratio of predictable components (RPC) is examined globally, as well as for regional climate indices: the North Atlantic Oscillation, Arctic Oscillation, Southern Annular Mode, and an Arctic index. Our analyses reveal significant correlations between the multi‐model ensemble‐mean and observations over large portions of the globe, particularly the tropics, North Atlantic, and North Pacific. However, RPC values greater than one are apparent over many extratropical regions and in all four climate indices. Higher‐resolution models produce greater observation‐model correlations and greater RPC values than lower‐resolution models in all four climate indices. We find that signal‐to‐noise errors emerge more clearly at higher resolution, but the amplitudes of predictable signals do not increase with resolution, at least across the range of resolutions considered here. Our results suggest that free‐running atmospheric models underestimate predictable signals in the absence of sea surface temperature biases, implying that signal‐to‐noise errors originate in the atmosphere or in ocean–atmosphere coupling. [ABSTRACT FROM AUTHOR]

Subantarctic Mode Water is a water mass with nearly vertically homogeneous physical properties in the Southern Ocean, which exhibit variability at various time scales. This study investigates the low-frequency variability of upper-ocean temperature in the Central Pacific Subantarctic Mode Water (CPSAMW) formation region since the 1980s using an eddy-resolving ocean model and two observation-based products. It is found that the CPSAMW core layer temperature has significant low-frequency variability, with an unusually cold period around 2000 and warm periods around 2005 and 2015, respectively. This low-frequency variability is closely related to the change in local mixed layer temperature, which in turn is mainly attributed to the change in surface latent heat flux resulting from the change in wind speed. Further analysis indicates that the low-frequency variability of wind speed in the CPSAMW formation region is dominated mainly by the Interdecadal Pacific Oscillation (IPO) and to a lesser extent by the Southern Annular Mode (SAM). This study reveals the relationship in the low-frequency variability of CPSAMW temperature with the IPO and SAM, and provides insight into the remote influence of Pacific decadal variability on SAMW variability. [ABSTRACT FROM AUTHOR]

Subantarctic Mode Water (SAMW) is one of the most important water masses for the global ocean uptake and storage of heat and carbon. Based on Argo observations, this study focus on the Southeast Indian Subantarctic mode water (SEISAMW), and investigates the changes of SEISAMW spreading and associated mechanisms. SEISAMW is formed through air‐sea interaction as low potential vorticity water in late winter and subducts into permanent thermocline between outcrop lines of 26.6 σθ and 26.9 σθ in Southern Indian Ocean (SIO). After subduction, the SEISAMW spreads northwestward into subtropical gyre and southeastward into Antarctic Circumpolar Current (ACC) separately. During Argo period, the percentage of SEISAMW volume spreading into SIO subtropics decreases at light layer (26.6–26.7 σθ) while increases at medium (26.7–26.8 σθ) and dense (26.8–26.9 σθ) layer. These changes are attributed to the meridional shifts of outcrop lines. The outcrop lines of 26.6 σθ and 26.7 σθ in the central of SIO (75°–90°E), where light SEISAMW forms, shift poleward. The poleward shifts of outcrop lines result in less light SEISAMW spreading into subtropical gyre. In contrast, outcrop lines of 26.7 σθ and 26.8 σθ south of Australia shift equatorward and favor more medium and dense SEISAMWs spreading into subtropical gyre. The shifts of outcrop lines are closely related to the enhancement of Southern Annular Mode. Plain Language Summary: Subantarctic mode water (SAMW), a water mass with vertically homogeneous properties, forms at the base of deep mixed layer during austral winter in the Subantarctic Zone, providing subsurface oceanic reservoirs of carbon and heat that can affect the global climate significantly. After subduction, SAMW that forms in Southern Indian Ocean (called SEISAMW) spreads into subtropical gyre and Antarctic Circumpolar Current (ACC). We find that the spreading of SEISAMW changes in different isopycnal layers during Argo period. The percentage of light SEISAMW volume spreading into subtropical gyre decreases, while the percentage of medium and dense SEISAMW volume spreading into subtropical gyre increases. The meridional shift of mode water formation region controls the change in spreading of SEISAMW here. The mode water formation regions shift oppositely in the central of SIO (where light mode water forms) and south of Australia (where the medium and dense mode water forms), and the opposite shifts of the formation regions result in the opposite changes in spreading of SEISAMW in the two isopycnal layers. This study reveals that the change of SEISAMW spreading is layer‐dependent, which would possibly improve our understanding of the heat redistribution process in the Southern Ocean. Key Points: The spreading of Southeast Indian subantarctic mode water (SEISAMW) changes during Argo periodThe changes in the spreading of light, medium and dense SEISAMWs are differentThe change of SEISAMW spreading is associated with change of formation region due to meridional shift of outcrop line [ABSTRACT FROM AUTHOR]

The current study explores the linkage and possible mechanisms of the Southern Annular Mode (SAM) with rainfall variability over southeastern South America (SESA). The findings indicate that the preceding May SAM can modulate the subsequent rainfall over the SESA region in September‐October‐November (SON), independent of the El Niño‐Southern Oscillation (ENSO) signal. Further analysis suggests that the SAM‐rainfall relationship is mainly due to the response of sea surface temperature (SST) in the subtropical and extratropical Southern Hemisphere to SAM variability via air‐sea interactions. Such SST anomalies persist to the subsequent SON and stimulate an upstream wave train extending into the study region from the South Pacific. Such wave patterns form a cyclone anomaly over SESA, indicating strong subsidence and reduced convection over the region. Meanwhile, the low‐level anomalous cyclone and anticyclone located over the subtropical South Atlantic (on the coast of the study region) are associated with easterly winds to the South (North) of the anomalous cyclone (anticyclone), which advect colder and drier air into the study region due to the cold SST over the subtropical South Atlantic and leading to increased moisture scarcity and decreased rainfall over SESA. Besides, model results based on the joint climate indices (i.e., SAM, ENSO and Indian Ocean Dipole (IOD)) revealed a satisfactory estimate of the SON rainfall compared with either single index, indicating that the SAM can be one of the precursors of the SESA rainfall, besides ENSO and IOD. Plain Language Summary: Drivers of rainfall variability over the southeastern South America (SESA) region in September–October–November (SON) include the tropical sea surface temperature (SST) and climate modes of variability, among which El Niño‐Southern Oscillation (ENSO) exerts the greatest influence. Though the Southern Annular Mode (SAM) has a concurrent influence on rainfall during this season, whether or not the SAM has a lead impact on the variability of SON rainfall in SESA has yet to be uncovered. Using reanalysis and satellite data, we found that the preceding May SAM can modulate the subsequent rainfall over the SESA region in SON without the ENSO influence. The SAM‐related SST anomalies in the extratropical and subtropical Southern Hemisphere are found to be important in establishing the link between SAM and rainfall through stimulating an upstream wave train pattern associated with a cyclone anomaly over the SESA region, contributing to suppressed moisture convection and reduced rainfall. In addition, model results constituting the SAM, ENSO and Indian Ocean Dipole lead combined indices can replicate well the temporal variations of SON rainfall compared to a single index, suggesting that the May SAM can improve the predictability of SON rainfall over SESA. Key Points: The preceding May Southern Annular Mode modulates the subsequent September–October–November rainfall conditions over southeastern South AmericaThe Southern Annular Mode‐induced sea surface temperature over the subtropical and extratropical Southern Hemisphere plays a key mediating role in linking the Southern Annular Mode to rainfallConsidering May Southern Annular Mode as a precursory signal can advance September‐October‐November rainfall predictability over southeastern South America [ABSTRACT FROM AUTHOR]

This study investigates the abrupt shift in the Southern Annular Mode (SAM), El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) and East Africa 'short rains' (EASR) during 1961, to understand the associated physical mechanisms. The mechanisms are examined through composite, correlation and regression analysis for the period 1901—2020, using multiple datasets. Findings show that in the pre-1961 period, SAM was associated with the EASR variability through its connection with the variability of the South Indian Ocean (SIO) sea surface temperature (SST) anomaly. The September SAM is related to a change in surface wind speed, which drive meridional oceanic Ekman transport and influence the surface heat exchange, redistributing heat near the surface. Warm SIO SST induces ascending motion throughout the atmosphere, favouring deep convection and Congo Basin westerlies, leading to enhanced EASR. The findings suggest that the September SAM provide an important forecasting signal for the EASR. However, post 1961, the SAM is decoupled from the EASR, and the IOD demonstrates a significant role in influencing the short rains. The anomalous Indian Ocean Walker circulation related to the IOD provides an essential driving process for anomalous moisture transport and convection in East Africa (EA), leading to EASR variability. The El Niño events predispose the Indian Ocean to positive IOD events, and thus, the absence of the former has ramifications to the EASR variability. The observational results show that prior to 1961, there was virtually no significant relation between the EASR and the zonal winds in the central equatorial Indian Ocean. The findings of this study have important implications for regional season climate prediction. [ABSTRACT FROM AUTHOR]

The present study investigates the lead relationship of the April–May (AM) Southern Annular Mode (SAM) with the northern Australia rainfall (NAR) variability in the subsequent December–February (DJF). The AM SAM was revealed to exhibit a considerable negative relationship with the NAR in the following DJF, which was still significant after removing the possible influence of El Niño–Southern Oscillation (ENSO). Further analysis revealed that the AM SAM can trigger the dipole sea surface temperature anomalies (SSTA) in the southern Indian Ocean through air-sea interactions. The dipole SSTA persists across the following months from June to September, and then it evolves to form the dipole SSTA at locations to the east of previous definitions of the Subtropical Indian Ocean Dipole from October to February of the following year. Based on the circulation anomalies, the AM SAM-related dipole SSTA in DJF is associated with an eastward shift of the Walker circulation between the tropical eastern Indian Ocean and the western Pacific Ocean, resulting in upward (downward) motion over the Indian (Pacific) Ocean and easterly surface wind anomalies across northern Australia. The anomalous easterlies are part of a localized anticyclonic circulation centred over the study region, which indicates diminished moisture influx into the northern parts of the continent, resulting in dry conditions over northern Australia. Besides, model results based on the preceding AM SAM and September ENSO indicate enhanced predictive skill of the NAR associated with combined indices compared to either single index. [ABSTRACT FROM AUTHOR]

The Southern Annular Mode (SAM) is the most dominant natural mode of variability in the mid‐latitudes of the Southern Hemisphere (SH). However, both the sign and magnitude of the feedbacks from the diabatic processes, especially those associated with clouds, onto the SAM remain elusive. By applying the cloud locking technique to the Energy Exascale Earth System Model (E3SM) atmosphere model, this study isolates the positive feedback from the cloud radiative effect (CRE) to the SAM. Feedback analysis based on a wave activity‐zonal momentum interaction framework corroborates this weak but positive feedback. While the magnitude of the CRE feedback appears to be secondary compared to the feedbacks from the dry and other diabatic processes, the indirect CRE effects through the interaction with other dynamical and thermodynamical processes appear to play as important a role as the direct CRE in the life cycle of the SAM. The cross‐EOF analysis further reveals the obstructive effect of the interactive CRE on the propagation mode of the SH zonal wind directly through the CRE wave source and/or indirectly through modulating other diabatic processes. As a result, the propagation mode becomes more persistent and the SAM it represents becomes more predictable when the interactive CRE is disabled by cloud locking. Future efforts on inter‐model comparisons of CRE‐denial experiments are important to build consensus on the dynamical feedback of CRE. Plain Language Summary: The annular mode is the most dominant mode of variability in the mid‐latitude atmospheric circulation system. Its origin, maintenance, and feedback mechanisms have long been the focus of atmospheric dynamics research. While its dry mechanisms are well understood, the role of the diabatic processes in the midlatitude storm tracks, especially the radiative effects of the cloud fields that evolve together with the storms, have not been quantified. Even the sign of the diabatic feedback to the annular mode remains a topic of debate. By disabling the cloud radiative feedback through a cloud‐locking technique that decorrelates the cloud fields with other dry and moist components in an atmospheric model, we are able to isolate the cloud radiative effect (CRE) throughout the life cycle of the Southern Annular Mode (SAM). Compared to the case with interactive CRE, the propagating SAM becomes more persistent and predictable in the cloud‐locking run, although the overall diabatic feedback to the standing dipole representation of the SAM is somewhat attenuated in this run. The diabatic and CRE feedbacks to the SAM identified here epitomize the sensitivity of the leading mode of the atmospheric variability to the model representation of the diabatic processes. Key Points: Cloud locking technique is used to isolate the interactive cloud radiative effect (CRE) on the Southern Annular Mode (SAM)Cloud radiative effect boosts the persistence of SAM as the leading EOF of the Southern Hemisphere zonal windThe interactive CRE feedback acts to weaken the cross‐EOF interaction and counter the poleward propagation of the zonal wind [ABSTRACT FROM AUTHOR]

Temporal and spatial variations in the ocean surface mixed layer are important for the climate and ecological systems. During 1980–2019, the Southern Indian Ocean (SIO) mixed layer depth (MLD) displays a basin‐wide shoaling trend that is absent in the other basins within 40°S–40°N. The SIO MLD shoaling is mostly prominent in austral winter with deep climatology MLD, substantially weakening the MLD seasonality. Moreover, the SIO MLD changes are primarily caused by a southward shift of the subtropical anticyclonic winds and hence ocean gyre, associated with a strengthening of the Southern Annular Mode, in recent decades for both winter and summer. However, the poleward‐shifted subtropical ocean circulation preferentially shoals the SIO MLD in winter when the meridional MLD gradient is sharp but not in summer when the gradient is flat. This highlights the distinct subtropical MLD response to meridional mitigation in winds due to different background oceanic conditions across seasons. Plain Language Summary: The ocean surface mixed layer (ML) is a well‐mixed layer with uniform physical and chemical properties and is key for the ocean in exchanging materials and energy with the atmosphere. The present study shows that during 1980–2019, the Southern Indian Ocean (SIO) ML depth (MLD) displays a basin‐wide decreasing trend, which is absent in the other basins within 40°S–40°N. The SIO MLD shoaling primarily appears in austral winter when the climatology ML is deep but is insignificant in summer, substantially weakening the MLD seasonality. The SIO MLD changes are primarily explained by the ocean dynamical adjustment driven by the surface zonal wind changes. Specifically, the strengthened Southern Annular Mode in recent decades drives southward shifts of the subtropical anticyclonic winds and ocean gyre year‐round. However, the poleward‐shifted ocean gyre preferentially decreases the SIO winter MLD as the meridional MLD gradient is sharp and thus efficiently reduces the deep ML water converging from the Southern Ocean into the SIO. In contrast, the SIO MLD displays negligible change in summer when its meridional gradient is flat. The results highlight that despite under nearly identical southward‐shifted subtropical winds, the winter and summer MLD responses are distinct due to different background oceanic conditions. Key Points: The seasonality of the Southern Indian Ocean surface mixed layer (ML) depth prominently weakens during 1980–2019The weakened seasonality mainly results from a pronounced winter ML shoalingThe southward shift of the subtropical ocean gyre driven by the strengthened Southern Annular Mode dominates the ML shoaling [ABSTRACT FROM AUTHOR]

The bimodal wave climate of the semi-protected shallow Gulf St Vincent in South Australia has been analyzed through a forty-year (1980-2020) wave hindcast and an investigation into the climatic drivers of wave climate anomalies is presented. The sea and swell partitions of the wave climate were modelled independently as well as using an integrated model with both partitions represented. The wave hindcast was validated against two wave buoys located off the coast of Adelaide’s metropolitan beaches and key wave parameter anomalies were calculated across the gulf. Teleconnections were investigated, and the Southern Annular Mode is found to have the strongest correlations to wave parameter anomalies while the Southern Oscillation Index and the Dipole Mode Index fluctuations are found to correlate seasonally with wave parameter anomalies. Projected future trends of these climate drivers from literature have been related to the teleconnections found in this study to inform future trends of bimodal wave conditions in the gulf. The Southern Annular Mode is projected to trend positive which will reduce wave height and the westerly component of waves in the gulf, while the Southern Oscillation Index is projected to become more variable in the future which will lead to more extreme winter and spring wave conditions. An understanding of these trends allows coastal managers to pre-emptively manage the impacts of waves on the coastline at a seasonal to annual basis and provides insight into future wave conditions beyond these time periods.

Surface melt in East Antarctica is strongly correlated with the Southern Annular Mode (SAM) index, but the spatiotemporal variability of the relationship, and the physical processes responsible for it, have not been examined. Here, using melt flux estimates and climate variables from the RACMO2.3p3 regional climate model, we show that a decreasing SAM index is associated with increased melt in Dronning Maud Land primarily owing to reduced precipitation and greater absorption of solar radiation. Conversely, in Wilkes Land, a decreasing SAM index corresponds to increased melt because of greater incoming longwave radiation from a warmer atmosphere. We also demonstrate that SAM‐melt correlations are strongest in December as the melt season develops, and that the SAM's influence on peak melt intensities in January occurs indirectly through the snowmelt‐albedo feedback. Future work must account for such variability in the physical processes underlying the SAM‐melt relationship to reduce uncertainty in surface melt projections. Plain Language Summary: The Southern Annular Mode (SAM) index describes the strength and location of the westerly winds in the Southern Hemisphere. It has previously been linked to interannual variability in the number of satellite‐observed melt days on the surface of East Antarctica's floating ice shelves. Here, we use melt estimates from a regional climate model adapted for the polar regions to show that the SAM‐melt relationship is also observed for meltwater fluxes, and to identify the influence of the SAM on the different energy sources driving surface melt. We find that a more negative SAM index (weaker westerlies) is associated with higher air temperatures across most of East Antarctica, and leads to increased incoming longwave radiation and sensible heat fluxes in Wilkes Land. In contrast, in Dronning Maud Land (DML), incoming longwave radiation is unaffected by the SAM, leading to net longwave energy losses, and sensible heat fluxes are reduced because of weaker surface winds. Instead, greater melt in DML is driven through increased absorption of solar radiation, owing to reduced precipitation and a darker surface. We also find differences in the strength of the SAM‐melt relationship on both sub‐seasonal and decadal timescales. Key Points: Modeled surface meltwater fluxes on East Antarctic ice shelves are negatively correlated with the Southern Annular Mode (SAM) indexMelt fluxes increase for a decreasing SAM index owing to reduced precipitation in Dronning Maud Land, and a warmer atmosphere in Wilkes LandThe SAM‐melt relationship is stronger in December than January, highlighting the importance of the snowmelt‐albedo feedback [ABSTRACT FROM AUTHOR]

This study investigates the relationship between circulation patterns and austral summer temperature anomalies in southern Africa. The results show that the formation of continental lows tends to increase the thickness of the lower atmosphere. Further, the distinct variabilities of high and low pressure under the circulation types, influence air mass advection from the adjacent oceans, as well as atmospheric stability over land. Stronger anticyclonic circulation at the western branch of the Mascarene high-pressure system enhances the low-level cold air advection by southeast winds, decreases the thickness, and lowers the temperature over a majority of the land in southern Africa. Conversely, a weaker Mascarene High, coupled with enhanced cyclonic activity in the southwest Indian Ocean increases low-level warm air advection and increases temperature anomalies over vast regions in southern Africa. The ridging of a closed South Atlantic anticyclone at the southern coast of southern Africa results in colder temperatures near the tip of southern Africa due to enhanced low-level cold air advection by southeast winds. However, when the ridge is weak and westerly winds dominate the southern coast of southern Africa, these areas experience temperature increases. The northward track of the Southern Hemisphere mid-latitude cyclone, which can be linked to the negative Southern Annular Mode, reduces the temperature in the southwestern part of southern Africa. Also, during the analysis period, El Niño was associated with temperature increases over the central parts of southern Africa; while the positive Indian Ocean dipole was linked to a temperature increase over the northeastern, northwestern, and southwestern parts of southern Africa. [ABSTRACT FROM AUTHOR]

The impacts of large‐scale climate variability on the current system and meridional transport in the Cosmonauts Sea off East Antarctica are studied by employing the satellite‐observed absolute dynamic topography (ADT) data and reanalysis hydrographic data. Three currents converge in the Cosmonauts Sea: the Antarctic Circumpolar Current (ACC), the Weddell Gyre Eastern Branch (WGeb) and the Antarctic Slope Current (ASC) containing the Antarctic Slope Front (ASF) topographically locked in the slope region. Strong seasonal and interannual variations are associated with these currents. The ACC and ASC are both stronger in autumn and weaker in spring and summer, while the WGeb extends eastward in winter and retreats in summer. On the interannual timescale, the Southern Annular Mode (SAM) reinforces the westerlies during its positive phase, pushing the ACC southward and suppressing westward ASC, and vice versa. The results on related mechanisms suggest the significant barotropic modulations induced by the winds on ocean dynamics from both the sea surface and interior ocean. The westerlies could affect the meridional sea level gradient through Ekman transport convergence, inducing the geostrophic adjustment of currents. Moreover, the vorticity input from the wind field produces meridional water transport under the topographic and planetary β‐effects, potentially influencing the structure of the ASF and associated ASC. This frontal adjustment is superimposed on the background barotropic variations and causes strong local responses of the currents to the remote wind forcing, which indicates a propagation of variability signals from large‐scale barotropic circulations to frontal‐scale baroclinic currents in the ocean interior. Plain Language Summary: Seasonal and interannual variations in the large‐scale wind field can affect the strength and position of the current system in the region around the Cosmonauts Sea off East Antarctica. The Antarctic Circumpolar Current (ACC), the Weddell Gyre Eastern Branch (WGeb) and the Antarctic Slope Current (ASC) meet around the Cosmonauts Sea. The surface current velocities and variations based on satellite‐observed sea surface height (SSH) data are computed, and the potential forcing mechanisms are analyzed. The strengths of the ACC and ASC change similarly in different seasons but oppositely in different years, along with the changes in the wind belts over the Southern Ocean. The results from studies indicate that the wind field plays an important role in forcing water motions, not only at the sea surface to change the SSH but also at depth to influence the water mass structure. These processes could further regulate the ACC and the ASC, enabling the large‐scale wind field to force into the narrow current jets associated with water mass fronts and topographic slopes. Key Points: Three main currents converging in the Cosmonauts Sea form an integrated circulation system with interconnected variationsWinds exert critical barotropic modulations on water transport in both the surface and deep layersAdjustment of Antarctic Slope Front north of Cape Ann can be triggered by interior ocean transport variations driven by wind stress curl [ABSTRACT FROM AUTHOR]

Accompanying global warming, Antarctic sea-ice extent shows a somewhat increasing trend from 1979 to 2014, followed by an abrupt decrease after 2016. Our previous study examined the change of Antarctic sea-ice extent in austral summer, autumn and spring. In this study, we turn our attention to the austral winter, relating the main modes of sea-ice variability to sea-ice extent in the Pacific, Atlantic and Indian sectors of the Southern Ocean. We find that the modes with the strongest correlation with the sea-ice extent are the third, first and first modes in the Pacific, Atlantic and Indian sectors, respectively. Atmospheric circulation anomalies of zonal wavenumber three over the Southern Ocean, related to planetary wave trains induced by the SST anomalies over the south-western Pacific and the southern Indian oceans, can explain sea-ice concentration anomalies of the third mode in the Pacific sector through thermodynamic and dynamic processes. Sea-ice anomalies of the first modes in the Atlantic and Indian sectors result from atmospheric circulation anomalies of a positive and negative phases of the Southern Annular Mode, respectively. The anomalous Southern Annular Mode is also associated with wave trains over the Southern Ocean excited by SST anomalies over the southern Indian Ocean and the south-western Pacific Ocean. The relationship between SST anomalies and Antarctic sea-ice anomalies can provide a reference for the prediction of Antarctic sea-ice anomalies in austral winter on interannual and decadal timescales. [ABSTRACT FROM AUTHOR]

The subantarctic zone is an important region in the Southern Ocean with respect to its influence on air‐sea CO2 exchange and the global ocean carbon cycle. However, understanding of the magnitude and drivers of the flux are still being refined. Using observations from the Southern Ocean Time Series (SOTS) station (∼47°S, 142°E) and auxiliary data, we developed a multiple linear regression model to compute the sea surface partial pressure of CO2 (pCO2) over the past two decades. The mean amplitude of the pCO2 seasonal cycle between 2004 and 2021 was 44 μatm (range 30–54 μatm). Summer minima ranged from 310 to 370 μatm and winter maxima were near equilibrium with the atmosphere. The non‐thermal (i.e., biological processes and mixing) contribution to the seasonal variability in pCO2 was several times larger than the thermal contribution. The SOTS region acted as a net carbon sink at annual time scales, with mean magnitude of 6.0 mmol m−2 d−1. The positive phase of the Southern Annular Mode (SAM) increased ocean carbon uptake primarily through an increase in wind speed at zero time lag. Increased surface pCO2 was correlated with a positive SAM with a lag of 4 months, mainly due to reduced biological uptake and increased mixing. During the autotrophic season, pCO2 was predominantly impacted by primary productivity, whereas water mass movement, inferred by temperature and salinity anomalies, had a larger impact on the heterotrophic season. In general, mesoscale processes such as eddies and frontal movement impact the local biogeochemical features more than the SAM. Key Points: An MLR model was built based on Southern Ocean Time Series data, to simulate surface pCO2 in the Australian sector subantarctic zone over the last 20 yearsBiological productivity controls the seasonal variability of pCO2 and drives a net carbon sink over two decadesMesoscale processes, and to a lesser extent, the Southern Annular Mode, drive local air‐sea CO2 flux variability [ABSTRACT FROM AUTHOR]

Antarctic coastal polynyas are biological hotspots in the Southern Ocean that support the abundance of high-trophic-level predators and are important for carbon cycling in the high-latitude oceans. In this study, we examined the interannual variation of summertime phytoplankton biomass in the Marguerite Bay polynya (MBP) in the western Antarctic Peninsula area, and linked such variability to the Southern Annular Mode (SAM) that dominated the southern hemisphere extratropical climate variability. Combining satellite data, atmosphere reanalysis products and numerical simulations, we found that the interannual variation of summer chlorophyll-a (Chl-a) concentration in the MBP is significantly and negatively correlated with the spring SAM index, and weakly correlated with the summer SAM index. The negative relation between summer Chl-a and spring SAM is due to weaker spring vertical mixing under a more positive SAM condition, which would inhibit the supply of iron from deep layers into the surface euphotic layer. The negative relation between spring mixing and spring SAM results from greater precipitation rate over the MBP region in positive SAM phase, which leads to lower salinity in the ocean surface layer. The coupled physical-biological mechanisms between SAM and phytoplankton biomass revealed in this study is important for us to predict the future variations of phytoplankton biomasses in Antarctic polynyas under climate change. [ABSTRACT FROM AUTHOR]

Aims: We investigate the associations between major Australian climate drivers and extreme weekly fire danger throughout the year. Methods: We use a composite-based approach, relating the probability of top-decile observed potential fire intensity to the positive and negative modes of the El Niño Southern Oscillation, Indian Ocean Dipole, Madden–Julian Oscillation, Southern Annular Mode, split-flow blocking and Subtropical Ridge Tasman Highs, both concurrently and at a variety of lag times. Key results: The chance of extreme fire danger increases over broad regions of the continent in response to El Niño and positive Indian Ocean Dipole events, the negative mode of the Southern Annular Mode, split-flow Blocking Index and Subtropical Ridge Tasman High, and Madden–Julian Oscillation phases 5, 6, 2 and 8 in Austral summer, autumn, winter and spring respectively. These relationships exist not only concurrently, but also when a climate event occurs up to 6 months ahead of the season of interest. Conclusions: These findings highlight the importance of considering the influence of diverse climate drivers, at a range of temporal lag periods, in understanding and predicting extreme fire danger. Implications: The results of this study may aid in the development of effective fire management strategies and decision-making processes to mitigate the impacts of fire events in Australia. This paper explores the relationships between the major forces influencing Australian weather and climate, and the chance of severe fire seasons. The findings could be valuable in decision making and preparation for upcoming fire seasons to avoid more seasons with devastating outcomes such as the 2019–2020 Black Summer. This article belongs to the Collection Fire and Climate. [ABSTRACT FROM AUTHOR]

This study investigates the interannual cross‐seasonal association between the winter energetic particle precipitation, which is related to the geomagnetic activity (GA), and the southern annular mode (SAM) in the following summer by employing the ERA5 reanalysis dataset. The results reveal a marked negative correlation between these variables on an interannual timescale. Therefore, we analyse the GA signatures in the southern atmosphere and find that the evolution of SAM to the negative phase driven by GA may be caused by the following two mechanisms: First, for high GA levels, the middle and lower stratospheric polar vortex becomes weaker from October to November, with considerable changes in the stratospheric thermal structure and more anomalous planetary wave upwelling, accompanied by weakening of the circumpolar westerly. Over time, the anomalous signal from the upper layer can be transmitted downward and is conducive to inducing and strengthening the negative SAM in the following summer, which may serve as the stratospheric pathway for the geomagnetic impact on the SAM and Southern Hemisphere (SH) climate. Second, another possible way is that the preceding GA also appreciably regulates negative anomalies in the Ferrel circulation in SH, implying poleward anomalies in the direction of the pressure gradient, which promotes the development and enhancement of the negative phase of the SAM. In addition, easterly quasi‐biennial oscillation conditioning plays a positive role in the response of the southern atmosphere to geomagnetic forcing, thereby strengthening the connection between them. [ABSTRACT FROM AUTHOR]

Interannual climate modes, especially the southern annular mode (SAM), significantly influence the wave climate modulation of the Indian Ocean (IO). The present study, aligned with previous research, identifies two crucial swell generation regions in the IO: the extratropical southern Indian Ocean (ETSI) and the tropical southern Indian Ocean (TSIO). The SAM, governing Southern Ocean surface winds, significantly shapes wave generation in these zones, thereby dominantly regulating IO wave conditions. Positive SAM phases shifts the westerlies poleward creating significant negative anomalies in the northern ETSI, reducing wave generation and swell propagation into the northern IO (NIO) basins, while the positive wind anomalies in the western TSIO creates a new swell generation area that directs swells towards the Arabian Sea, elevating wave heights there during monsoons. Conversely, negative SAM phases enhance TSIO easterlies, making it the primary IO swell source, increasing swell activity in the Bay of Bengal, notably during premonsoon and monsoon seasons. SAM impact expands beyond swells, influencing NIO wave climate by altering wind seas through Hadley cell (HC) circulation shifts. Positive SAM phases trigger NIO and midlatitude anomalous warming, intensifying HC and NIO surface winds in the next season, thereby affecting convection and subsequent sea surface temperature (SST) anomaly changes. The "SAM positive anomaly wind‐SST oscillations (SPAWSO)" pattern emerges, where warm SST anomalies in DJF and JJA precede increased surface winds in MAM and SON, thus increasing the wind‐sea conditions in the NIO. SPAWSO, hence, acts as a delayed mode, season‐dependent positive air–sea interaction cycle linked to positive SAM phases, significantly impacting NIO's wind‐sea dynamics. Thus the present study provides better insights into the long‐term wave prediction accuracy in the IO by considering the direct swell influence and SPAWSO‐driven wind‐sea changes, aiding preparations for changing wave dynamics and their impacts. [ABSTRACT FROM AUTHOR]

The large-scale extratropical circulation in the Southern Hemisphere is much more zonally symmetric than that of the Northern Hemisphere, but its zonal departures, albeit highly relevant for regional impacts, have been less studied. In this study we analyse the joint variability of the zonally asymmetric springtime stratospheric and tropospheric circulation using Complex Empirical Orthogonal Functions (cEOF) to characterise planetary waves of varying amplitude and phase. The leading cEOF represents variability of a zonal wave 1 in the stratosphere that correlates slightly with the Symmetric Southern Annular Mode (S-SAM). The second cEOF (cEOF2) is an alternative representation of the Pacific-South American modes. One phase of this cEOF is also very highly correlated with the Asymmetric SAM (A-SAM) in the troposphere. Springs with an active ENSO tend to lock the cEOF2 to a specific phase, but have no consistent impact on its magnitude. Furthermore, we find indications that the location of Pacific Sea Surface Temperature anomalies affect the phase of the cEOF2. As a result, the methodology proposed in this study provides a deeper understanding of the zonally asymmetric springtime extratropical SH circulation. [ABSTRACT FROM AUTHOR]

This study identifies a new triggering mechanism of the Indian Ocean Dipole (IOD) from the Southern Hemisphere. This mechanism is independent from the El Niño-Southern Oscillation (ENSO) and tends to induce the IOD before its canonical peak season. The joint effects of this mechanism and ENSO may explain different lifetimes and strengths of the IOD. During its positive phase, development of sea surface temperature cold anomalies commences in the southern Indian Ocean, accompanied by an anomalous subtropical high system and anomalous southeasterly winds. The eastward movement of these anomalies enhances the monsoon off Sumatra-Java during May–August, leading to an early positive IOD onset. The pressure variability in the subtropical area is related with the Southern Annular Mode, suggesting a teleconnection between high-latitude and midlatitude climate that can further affect the tropics. To include the subtropical signals may help model prediction of the IOD event.

The sea‐ice extent (SIE) in the Weddell Sea plays a crucial role in the Antarctic climate system. Many studies have examined its long‐term trend, however whether its year‐to‐year variation has changed remains unclear. We found an amplified year‐to‐year variance of the Weddell Sea SIE in austral summer since 1998/1999 in observational datasets. Analyses of sea‐ice concentration budget and surface fluxes indicate that it is the thermodynamic process that drives the amplification of SIE variations, rather than the sea‐ice‐drift‐related dynamic process. Compared to 1979–1998, the Southern Annular Mode in the preceding spring shows a closer linkage with the Weddell Sea SIE in 1999–2021 through a stronger and more prolonged impact on sea surface temperature, which thermodynamically modulates local sea ice via changing surface heat and radiation fluxes. Our study helps advance the understanding of extreme low Antarctic‐SIE records occurring in recent decades and improve future projections of the Antarctic sea‐ice variability. Plain Language Summary: Unlike Arctic sea ice, which has significantly declined in recent decades, Antarctic sea ice possesses a moderate increase with large spatial and seasonal discrepancies. The amount of austral‐summer sea ice extent (SIE) around the Antarctica exhibits more pronounced year‐to‐year variations in the 21st century. Interestingly, we found that the amplified SIE variation is most significant in the Weddell Sea, east of the Antarctic Peninsula. This amplified variations in Weddell Sea SIE apparently cannot be fully explained by anthropogenic forcing, suggesting an important role of internal variability in the Antarctic climate system. Our analyses showed that the late‐1990s changes in the Southern Annular Mode (SAM)—the predominant mode of climate variability in the extratropical Southern Hemisphere—might cause the interdecadal amplification of the summer sea‐ice variation in the Weddell Sea via the thermodynamic process. Key Points: The year‐to‐year variability of summer sea‐ice extent in the Weddell Sea, Antarctica, has significantly increased since 1998/1999This interdecadal change in sea‐ice extent is dominated by changes in thermodynamic process rather than dynamic and mechanical processesThe Southern Annular Mode contributes to such a sea‐ice change via altering sea surface temperature and thus local thermodynamic processes [ABSTRACT FROM AUTHOR]

Heatwaves in the Southern Hemisphere (SH) occur frequently but have received little attention over the years. This study presents a comprehensive analysis of a long-duration, wide-ranging, and high-intensity heatwave event in South America spanning from 9 to 16 January 2022. Before the heatwave occurred, the meridional sea surface temperature (SST) in the SH intensified due to the warming of the South Pacific, while the Southern Annular Mode (SAM) exhibited a positive phase. As a result, the intensified wave activities in the westerlies led to high-pressure anomalies in South America, which played a dominant role in the generation of the heatwave. The diagnostic analysis of thermodynamic equations in South America indicates that the temperature increase during the heatwave was primarily caused by the vertical advection term. In contrast, horizontal advection had a negative impact on surface warming. Additionally, the diabatic heating term associated with surface land types serves as a significant factor that cannot be disregarded. This study aims to deepen our understanding of the mechanisms underlying heatwave generation in South America, enabling the improved prediction of heatwaves and enhanced assessment of potential risks in the future. [ABSTRACT FROM AUTHOR]

Extreme ocean surface waves can significantly impact the coastal and offshore-related activities, and often cause large-scale destruction to the livelihoods of the coastal population. To potentially reduce the adverse societal impacts and planning operations, it is necessary to assess the futuristic changes in extreme wave climate. This study examined the extreme wave height indices described by the Expert Team on Climate Change Detection and Indices (ETCCDI) for the Indian Ocean (IO) obtained from Coordinated Ocean Wave Climate Projections, Phase 2 (COWCLIP2.0) historical simulations and projected datasets. A multi-model ensemble (MME) approach is employed to study the projected changes under RCP4.5 and RCP8.5 emission scenarios. Substantial increases in rough wave days are projected over the northern sector of the Arabian Sea (AS) and eastern tropical IO (TIO). The projected changes in high wave days and wave-spell-storm duration under both the scenarios are observed in southern IO. On the contrary, widespread projected decreases in rough wave days are evident over the central TIO, and in wave-spell-storm duration for the southern sector of AS. A strong teleconnection between the projected changes in wave extremes in IO is consistent with the projected changes in sea level pressure gradient (SLPG). Further, in southern IO, the Southern Annular Mode (SAM) has strong association with extreme wave indices. [ABSTRACT FROM AUTHOR]

The variability of Indian Ocean shallow meridional overturning circulation (SMOC) is studied using the century long ocean reanalysis simple ocean data assimilation (SODA) data. Though SMOC exhibits stronger southward transport during boreal summer, it displays stronger variability during boreal winter. The spectrum analysis of winter SMOC index reveals presence of highest amplitude between 5 to 7 years at 95% confidence level, suggesting the dominance of intra-decadal SMOC variability. The robustness of intra-decadal SMOC variability is also confirmed in different ocean reanalysis data sets. Composite analysis of filtered upper Ocean Heat Content, sea level, thermocline depth and Sea Surface Temperature anomalies for strong (weak) SMOC years show negative (positive) anomaly over north and East of Madagascar. Correlation analysis, of filtered SMOC index and sea level pressure (zonal winds) over the India Ocean, found significant negative (positive) correlation coefficient north of 40 °S (around 10 °S) and significant positive (negative) correlation coefficient over the 45 °S to 70 °S (20 °S to 50 °S and north of 5 °S). This meridional pattern of correlation coefficient for sea level pressure, manifesting the out of phase relationship between sub-tropics and high latitude mean sea level pressure, resembles with Southern Annular Mode (SAM). We conclude that the intra-decadal variability of mean sea level pressure leads to zonal wind variation around 10 °S modulating SMOC, which in turn affects the upper ocean thermal properties in the east and north of Madagascar. This study for the first time brought out coherent intra-decadal evolution of SAM and SMOC during boreal winter. [ABSTRACT FROM AUTHOR]

The Southern Westerly Wind (SWW) belt is one of the most important atmospheric features of the Southern Hemisphere (SH). In Patagonia, these winds control the precipitation rates at the windward side of the southern Andes, and rainfall is very sensitive to any change (strength and/or latitudinal position) in the wind belt. The present-day behavior of the SWW, also known as westerlies, is characterized by remarkable seasonality. This wind belt also varies at interannual-to-decadal time scales, associated with the influence of atmospheric phenomena such as the El Niño–Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO), respectively. Moreover, during the past few decades, the westerlies have shown an increase in their core strength influenced by changes in the Southern Annular Mode (SAM). However, what controls the long-term variability of the SWW at the high latitudes of the SH is still a matter of debate. This work statistically analyzes the influence of large-scale modes of variability, such as ENSO and PDO on the SAM and the frequency of the strong SWW from ERA5 reanalysis data of southwestern Patagonia (~51°S), where the current core of this belt is located. Our results confirm the relation between strong wind anomalies and the SAM. In addition, the temporal variations of strong winds are also significantly affected by the PDO, but there is no detectable influence of the ENSO on their frequency. This shows that future studies focused on reconstructing wind history from aeolian particles of lake sediments from southwestern Patagonia could also provide information about the modes of variability that influence strong wind frequency. [ABSTRACT FROM AUTHOR]

The Southern Hemisphere westerly winds (SWW) play a critical role in global climate, yet their behavior on decadal to centennial timescales, and the mechanisms driving these changes during the preindustrial era, remain poorly understood. We present a decadally resolved record of dust compositions using strontium and neodymium isotope ratios in mineral dust from the Siple Dome ice core, Antarctica, to explore the potential that abrupt changes in SWW behavior occurred over the past millennium. The record spans portions of the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) intervals as defined in the Northern Hemisphere. We find evidence of an abrupt strengthening of atmospheric circulation during the MCA at ∼1125 CE (825 BP) that persisted for about 60 yr, indicating increased influence of Patagonia‐sourced dust. This occurs during an extended positive phase of Southern Annular Mode (SAM+)‐like conditions, characterized by high SWW velocities and a southerly shift of the main wind belt toward ∼60°S, suggesting that rapid changes in SWW strength could occur under the present SAM+ pattern. A second 20 yr long shift in dust compositions during the LIA at ∼1748 CE (200 BP) is coincident with higher dust delivery to Siple Dome, and may indicate increased dust emissions related to glacier activity in Patagonia. The new Siple Dome ice core data set demonstrates that Sr‐Nd isotopes can be used to trace shifts in atmospheric circulation on decadal timescales. Plain Language Summary: The prevailing winds that encircle Antarctica, blowing west to east, play an outsized role in global climate. Because they blow continuously over the ocean, they create ocean currents and cause upwelling. When deep ocean water comes to the surface, it releases carbon dioxide into the atmosphere, causing the climate to warm. Changes in wind strength and positioning modulate the release of carbon dioxide. Therefore, knowing how and why the winds shift is important for understanding how Earth's climate system operates. We use the composition of dust preserved in an Antarctic ice core to learn how the balance of dust sources changed during the past millennium. This allows us to track past shifts in the winds around Antarctica and to learn how they respond to climate changes on short timespans, such as decades to centuries. We observe an abrupt change in dust composition at ∼1125 CE lasting for about 60 yr, indicating a greater influence of dust sourced from Patagonia in South America. This dust shift occurred during a globally observed warm period, and corresponded with an interval of stronger westerly winds blowing closer to Antarctica. Our data show that decade‐scale changes can be superimposed on longer intervals of intensified wind strength. Key Points: An ice core dust provenance record from Siple Dome shows marked shifts at about 1125 CE (lasting ∼60 yr) and 1748 CE (∼20 yr)Sr‐Nd isotopes indicate changes in the relative deposition of dust from Patagonian and Antarctic sources driven by changes in windsData suggest decade‐scale changes can be superimposed on longer intervals of intensified westerly wind strength during SAM + ‐like phases [ABSTRACT FROM AUTHOR]

This study investigates the influence of the Southern Annular Mode (SAM) on chlorophyll- a (Chl- a ) concentrations and the underlying mechanisms governing their associated environmental variations in the mid-latitude (35–50° S) ocean from 1998 to 2021. The intensification of westerly winds during positive SAM phases influences meridional water transport and mixed layer depth (MLD), which are both critical factors that affect surface nutrient availability. A marked contrast in the relationship between the meridional current anomaly and the SAM was observed, with reduced northward transport of nutrient-rich water in regions north of 50° S during positive SAM phases. This reduction could be attributed to the poleward migration of the westerly winds, which impeded the meridional current from reaching the mid-latitudes. The relationship between SAM and MLD south of 50° S was positive whereas that in the mid-latitude eastern (60–110° E) South Indian Ocean and eastern (90–140° W) South Pacific Ocean was negative or weak. The immediate effect of a more positive SAM on Chl- a in the mid-latitude ocean was reduced productivity caused by enhanced nutrient depletion. However, in the mid-latitude eastern South Pacific Ocean, the northward migration of the zonal mean meridional current anomaly closely aligned with the lagged correlation pattern between SAM variability and Chl- a over time, suggesting that the delayed northward transport of nutrient-rich waters may partially counterbalance the immediate effects of the SAM on ocean productivity. This mechanism was not present in the mid-latitude eastern South Indian Ocean, implying that future climate change may variably affect these regions. Our findings emphasize the importance of considering regional differences and temporal lags when evaluating the influence of SAM variability on ocean productivity and nutrient dynamics in the context of climate change.

Abstract The variability of the Southern Hemisphere (SH) extratropical large‐scale circulation is dominated by the Southern Annular Mode (SAM), whose timescale is extensively used as a key metric in evaluating state‐of‐the‐art climate models. Past observational and theoretical studies suggest that the SAM lacks any internally generated (intrinsic) periodicity. Here, we show, using observations and a climate model hierarchy, that the SAM has an intrinsic 150‐day periodicity. This periodicity is robustly detectable in the power spectra and principal oscillation patterns (aka dynamical mode decomposition) of the zonal‐mean circulation, and in hemispheric‐scale precipitation and ocean surface wind stress. The 150‐day period is consistent with the predictions of a new reduced‐order model for the SAM, which suggests that this periodicity is associated with a complex interaction of turbulent eddies and zonal wind anomalies, as the latter propagate from low to high latitudes. These findings present a rare example of periodic oscillations arising from the internal dynamics of the extratropical turbulent circulations. Based on these findings, we further propose a new metric for evaluating climate models, and show that some of the previously reported shortcomings and improvements in simulating SAM's variability connect to the models' ability in reproducing this periodicity. We argue that this periodicity should be considered in evaluating climate models and understanding the past, current, and projected Southern Hemisphere climate variability.

Antarctic surface air temperature (SAT) variability is characterized by strong seasonality and regionality, which are associated with the tropical–polar teleconnections and the radiative forcing caused by the concentration changes in ozone and other greenhouse gases. Nevertheless, the sparse in situ observations and the strong disagreement between different reanalysis datasets hinder coherent conclusions about Antarctic SAT variability. In this study, we use a newly developed statistical method, combined maximum covariance analysis (CMCA), to retrieve coherent SAT modes from six reanalysis datasets and 26 station observations. The results show that the Antarctic SAT variability may be dominated by a continental-wide warming/cooling mode, an East–West Antarctic seesaw mode, and a dipole SAT mode around West Antarctica. These SAT modes are strongly associated with three principal modes of Antarctic atmospheric circulation. Furthermore, all six reanalyses can represent these SAT modes well, compared with the observations, despite a clear deviation over the Antarctic Peninsula associated with the biases in the Foehn wind, which may not be clearly reproduced in a low-resolution reanalysis. This study provides an effective means by which to extract coherent signals from all reanalyses and observations to represent the Antarctic SAT variability, and to improve its predictability and projection. [ABSTRACT FROM AUTHOR]

The Bransfield Strait is a climate change hotspot at the tip of the northern Antarctic Peninsula (NAP). The region is marked by a mixture of relatively warm waters from the Bellingshausen Sea with cold shelf waters from the Weddell Sea. Additionally, its deep central basin (>800 m) preserves seawater properties from the north‐western Weddell Sea continental shelf. This study assessed long‐term changes in carbonate chemistry in the Bransfield Strait and found that the hydrographic setting (i.e., a mixture between modified‐Circumpolar Deep Water with Dense Shelf Water [DSW]) drives temporal variability of carbonate parameters. The western basin has experienced decreases in pH (seawater scale) over the last three decades (1996–2019), varying from −0.003 to −0.017 pH units yr−1, while Ωar decreased from −0.01 to −0.07 yr−1 throughout the water column. The central basin was characterized by a high contribution of DSW with high carbon dioxide (CO2) content and the decomposition of organic matter produced and transported into its deep layer. With lower variability for all carbonate system variables, the eastern basin was likely regulated by internal mixing. Overall, the entire strait is almost reaching a CO2‐saturated condition, highlighting how sensitive subpolar regions are to the effects of human‐induced climate change. Plain Language Summary: Although the entire world is experiencing the impacts of climate change, they may be occurring more rapidly in some regions, such as the northern Antarctic Peninsula. At the northern tip of this area is the Bransfield Strait, which can act as a sentinel for identifying what is happening around the peninsula during modern climate change. Areas of the strait that are connected to the open ocean showed a more rapid increase in acidification over time than areas mainly influenced by coastal zones. This occurs because the contribution of open‐ocean water masses supplies a signature of the decomposition of organic particles from the ocean around Antarctica. On the other hand, coastal zones are more influenced by atmospheric carbon dioxide from human activities. The steeper acidification trends in the Bransfield Strait draw our attention to the effects of climate change on ocean acidification and its biological and chemical impacts on the ocean. Moreover, there are many areas, such as the Bransfield Strait, for which there are few studies about these effects, which delays the identification of severe impacts even after changes have already been experienced, as was found in our assessment. Key Points: The western basin experiences steeper pH decreases than the surrounding areas at a rate of −0.017 pHsws units yr−1 due to Circumpolar Deep Water intrusionsDense Shelf Water inflow into the deep layer of the central basin promoted a CT increase of about 50 μmol kg−1 in the 2010s relative to the 2000sInternal mixing has likely reduced spatiotemporal variability of carbonate chemistry in the eastern basin since the 1990s [ABSTRACT FROM AUTHOR]

Predicting the responses of populations in changing environments is an important task for ecologists. Understanding the population dynamics of high‐latitude breeding species is critical given the particularly rapid environmental changes that occur in these regions. Using long‐term mark–resighting data acquired over 53‐years in Pointe Géologie, Terre Adélie, Antarctica, we estimated age‐specific demographic parameters and evaluated the effect of the environment on survival of a poorly known species, the cape petrel Daption capense. We then modeled the dynamics of this population using a life‐history model and performed prospective and retrospective analyses to estimate the sensitivity of the population growth rate to demographic parameters, and to quantify their relative contribution. Survival of cape petrel increased with age, being 0.610 (±0.193) for juveniles, 0.739 (±0.158) for individuals from 2 to 4, and 0.920 (±0.031) for older individuals. Minimum age at first reproduction was 3 years old, the age at which all birds were recruited was 14 years, and mean age at first reproduction was 9.05 (±2.06) years. Adult survival increased over time and was positively correlated with the southern annular mode (SAM). The stochastic population growth rate was estimated at 1.019, and adult survival over age 5 made the largest contribution to variance of the population growth rate. Sensitivity analyses revealed that population regulation was mainly driven by the SAM. Our results suggest that despite the decrease in breeding success, the population of cape petrels at Pointe Géologie increased due to the increase in immature and adult survival. [ABSTRACT FROM AUTHOR]

Although on average, the southwestern Cape (SWC) of South Africa is a winter rainfall dominated region, almost 30% of the total rainfall occurs during the extended summer (October-March). A previous study showed that anomalously wet summers may help mitigate the effects of severe winter drought. Apart from that study, very little work has been done on summer rainfall variability over the SWC or the mechanisms associated with it. Here, station data and ERA5 reanalyses are used to investigated summer rainfall day variability and associated mechanisms. Interannual variability in summer rainfall day frequencies appears related to that in the South Atlantic High Pressure (SAHP) and westerly moisture fluxes across the midlatitude South Atlantic. Increased rainfall days are associated with cyclonic anomalies over the region and enhanced westerly moisture fluxes. Some of these circulation changes are related to the Southern Annular Mode, and in late summer, also to ENSO and changes in the zonal wavenumber 3 pattern. Significant decreasing trends in rainfall days were found in the mid- and late summer for the southern part of the region where most of the population lives and the main water supply dams are located. These trends seem associated with significant trends found in the southern boundary of the SAHP and in decreasing (increasing) South Atlantic storm counts in the 35°–45° S (50°–60° S) latitude bands. [ABSTRACT FROM AUTHOR]

There is growing interest in the international scientific community in characterizing climate variability in Antarctica because of the continent's fundamental role in regulating the world's climate. Researchers have intensively studied the Antarctic Peninsula since the warming that began in the mid‐1950s. This was followed by a subsequent cooling period over the last decades. For this paper, using the available data, we analysed the variability in surface air temperatures at five meteorological stations located on King George Island (KGI) (a subantarctic island that is part of the South Shetland Islands); we also investigated the relationships between the air temperatures and large‐scale atmospheric patterns from 1968 to 2019. In this study we found that summer temperatures are above 0°C from December to March and close to melting temperatures (extreme values) in spring and autumn; consequently, a small increase in temperature can have a significant impact on the cryosphere. The statistical analysis of the mean temperatures confirmed a trend toward cooling during the summer and in the mean monthly maximum temperatures over the 1990s at most of the weather stations whose data we analysed. Analysing the teleconnection patterns showed that the Southern Annular Mode (SAM) had strong, direct, and positive correlations during the autumn and less strong connections in spring, winter, and on an annual scale. Furthermore, we observed a lesser influence of El Niño‐Southern Oscillation (ENSO). [ABSTRACT FROM AUTHOR]

The impacts of Stratospheric Aerosol Injection (SAI) strategies on the Southern Annular Mode (SAM) are analyzed with the Community Earth System Model. Using a set of simulations with fixed single‐point SO2 injections we demonstrate the first‐order dependence of the SAM response on the latitude of injection, with the northern hemispheric and equatorial injections driving a response corresponding to a positive phase of SAM and the southern hemispheric injections driving a negative phase of SAM. We further demonstrate that the results can to first order explain the differences in the SAM responses diagnosed from the two recent large ensembles of geoengineering simulations utilizing more complex injection strategies – Geoengineering Large Ensemble and Assessing Responses and Impacts of Solar climate intervention on the Earth system with Stratospheric Aerosol Injection (GLENS and ARISE‐SAI) – as driven by the differences in the simulated sulfate aerosol distributions. Our results point to the meridional extent of aerosol‐induced lower stratospheric heating as an important driver of the sensitivity of the SAM response to the injection location. Plain Language Summary: Stratospheric Aerosol Injection (SAI) is a proposed climate intervention method in which sulfate aerosol precursors are injected into the lower stratosphere to mitigate some of the negative impacts of climate change. Here we analyze SAI impact on the Southern Annular Mode (SAM), a dominant mode of interannual climate variability in the southern mid‐ and high latitudes, using the Community Earth System Model. Using a set of simulations with fixed single‐point injections of aerosol precursors we demonstrate the first‐order dependence of the SAM response on the latitude of injection, with the northern hemispheric and equatorial injections driving a response corresponding to a positive phase of SAM and the southern hemispheric injections driving a negative phase of SAM. We further demonstrate that our results can to first order explain the differences in the SAM responses diagnosed from the two recent large ensembles of geoengineering simulations utilizing more complex injection strategies as driven by the differences in the simulated sulfate aerosol distributions. Our findings illustrate the complex interplay of the microphysical, radiative and dynamical processes contributing to the SAI responses on regional scales. Key Points: Stratospheric Aerosol Injection (SAI) impacts the Southern Annular Mode (SAM), and the response is strongly sensitive to the latitude of SAIInjections in the Northern Hemisphere drive positive SAM response and injections in the Southern Hemisphere drive negative SAM responseMeridional extent of lower stratospheric aerosol heating likely an important contributor to the sensitivity to injection latitude [ABSTRACT FROM AUTHOR]

Marine ecosystems in southeastern Australia are responding rapidly to climate change. We monitored the diet of the Australian fur seal (Arctocephalus pusillus doriferus), a key marine predator, over 17 years (1998–2014) to examine temporal changes. Frequency of occurrence (FO) of prey was used as a proxy for ecosystem change. Hard part analysis identified 71 prey taxa, with eight dominant taxa in greater than 70% of samples and predominantly included benthic and small pelagic fish. FO changed over time, e.g. redbait (Emmelichthys nitidus) reduced after 2005 when jack mackerel (Trachurus declivis) increased, and pilchard (Sardinops sajax) increased after 2009. Using generalized additive models, correlations between FO and environmental variables were evident at both the local (e.g. wind, sea surface temperature (SST)) and regional (e.g. El Niño–Southern Oscillation Index (SOI), Southern Annular Mode (SAM)) scales, with redbait and pilchard showing the best model fits (greater than 75% deviance explained). Positive SAM was correlated to FO for both species, and wind and season were important for redbait, while SOI and SST were important for pilchard. Both large-scale and regional processes influenced prey taxa in variable ways. We predict that the diverse and adaptable diet of the Australian fur seal will be advantageous in a rapidly changing ecosystem.

This study provides comprehensive analysis on the contrasting effects caused by the 1997 and 2015 historical El Niño events linked with the Indian Summer Monsoon (ISM) rainfall. The presence of strong southeast-northwest oriented cold Sea Surface Temperature (SST) anomalies during 1997, that spatially extended from southwest Pacific to Southeast Indian Ocean (SEIO) in comparison to the 2015 event is the robust feature. Evidently, these anomalies are closely related to interaction between cyclonic (anticyclonic) circulation over South Pacific Convergence Zone (south Australia). During 2015, the conjunction of Modoki II and classical El Niño triggered an asymmetrical equatorial circulation throughout the Indo-western Pacific (IWP) and thereby stimulated the Southern Annular Mode (SAM) through troposphere and stratospheric pathway mechanism. In addition, in 2015, SAM impacted the Indian Ocean, which intern affected ISM rainfall. Positive SAM associated with westward shift of anticyclone over south of Australia alters the circulation by inducing westerly winds over the South Indian Ocean, thereby suppressing Indian Ocean Dipole (IOD), and inducing drought conditions over India during 2015. Moreover, the AUS index, an indicator for IOD strength in boreal summer, is a bridging factor prevalent over mid-latitude regions in the southern hemisphere. Results from this study indicate the complex interaction of southern hemisphere atmospheric flow and its role in modulating the Indian Ocean region thereby ISM rainfall. A better understanding of these underlying mechanism can significantly enhance the predictive skills and projections of monsoon variability and extremes. • The 1997 and 2015 El Niño events differently impacted Indian Summer Monsoon rainfall patterns. • Shifts in Indo-Pacific SST and circulation anomalies noticed with notable changes in air-sea interaction among these events. • SAM shifts anticyclone westward south of Australia, enhancing SIO westerlies, suppressing IOD, causing India's 2015 drought. • AUS index, indicating IOD strength in boreal summer, a key bridging factor across the Southern Hemisphere's mid-latitudes. [ABSTRACT FROM AUTHOR]

Near-Surface Wind Speed (SWS) is a crucial but less studied climate variable in the northern Antarctic Peninsula (AP). This research evaluates, for the first time, 44 years (i.e., 1979–2022) of SWS trends and variability across the AP using two data sources: (i) observational data from quality-controlled and homogenized meteorological stations, and (ii) reanalysis data from ERA5; the accuracy of this product strongly depends on each station with an overall underestimation of observed SWS. Annual trends in observed SWS exhibit a positive trend, being statistically significant in autumn and spring, with a marked intraanual and spatial variability in the sign and magnitudes across the AP. In addition, the multidecadal variability of observed SWS showed a general positive trend until ∼2001 (varying between 1993 and 2007 depending on each season), followed by a period of slowdown in the last two decades. Over the AP, SWS changes are mainly driven by two principal modes of atmospheric variability: i.e., mainly the Southern Annular Mode (SAM) and, secondarily, by the El Niño-Southern Oscillation (ENSO). Overall, positive trends in SWS could be partly associated with the increase and poleward shift of the westerlies due to the positive trend of the SAM index. However, as previous studies pointed out for air temperature and precipitation, we found a non-stationary and complex relationship of these modes with SWS changes. This research addresses the gap in SWS changes and variability in the AP and surrounding Southern Ocean and the influence of the atmospheric circulation, a hotspot area in climate change research. • A recent slowdown of observed wind speed is reported in the Antarctic Peninsula, after positive trend phase. • ERA5 can reproduce observed wind speed variability, despite station-based differences are found. • Ocean-atmosphere oscillations partly explain the observed variability and changes in wind speed. • SAM influence in surface wind speed over the AP is non-stationary. [ABSTRACT FROM AUTHOR]

Surface winds around the Antarctic continent control coupled ocean‐ice processes that influence the climate system, including bottom water production, heat transport onto the continental shelf and sea ice coverage. However, few studies have examined projected changes in these winds, even though it would aid in the interpretation and understanding of the ocean's response to climate change. Using Coupled Model Intercomparison Project Phase 6 and reanalysis data, we show a significant reduction in the near‐Antarctic surface winds throughout the historical period that continues until the end of the twenty‐first century, amounting to 23% and 7% for the easterly and southerly wind components respectively under the high emission scenario. The most intense weakening happens during the summer season. We find that the weakening is coherent with the trend toward a positive Southern Annular Mode and a reduction of the pole‐to‐coast meridional pressure gradient, which we term Antarctic Annular Index. Plain Language Summary: Surface winds over the ocean around the Antarctic continent influence several aspects of the oceanic circulation and sea ice in the region that become relevant in the context of climate change. For example, Antarctic coastal surface winds have been found to drive the warming experienced in some regions that subsequently triggers increased ice shelf melt. However, there is little understanding regarding how this wind regime is expected to change in the future, with most research focusing on the mid‐latitude westerlies. In this work, we use Coupled Model Intercomparison Project Phase 6 models to quantify projected changes in these winds to the end of the twenty‐first century, hoping that it will aid in the interpretation of the ocean's response to climate change. Under the high emission scenario, we find a significant weakening of 23% for the easterly wind component and 7% for the meridional wind component. This weakening can be partly explained by a large‐scale pattern of change in sea level pressure that reflects in an increase of the atmospheric mode of variability known as the Southern Annular Mode, and a decrease of the pole‐to‐coast surface pressure gradient, which we term Antarctic Annular Index. Key Points: Coupled Model Intercomparison Project Phase 6 models show a weakening of the near‐Antarctic surface winds during the period 1979–2015Future projections in CMIP6 models show that the weakening trend continues until the end of the twenty‐first centuryWeakened winds are associated with a more positive Southern Annular Mode and a reduction in the pole‐to‐coast meridional pressure gradient [ABSTRACT FROM AUTHOR]

Improved understanding of the drivers of climate variability, particularly over the last millennium, and its influence on Antarctic ice melt have important implications for projecting ice sheet resilience in a changing climate. Here, we investigated the variability in Antarctic climate and sea ice extent during the last millennium (850–1850 CE) by comparing paleoenvironmental reconstructions with simulations from the Community Earth System Model Last Millennium Ensemble (CESM-LME). Atmospheric and oceanic response to external forcing in CESM-LME simulations typically take the form of an Antarctic dipole: cooling over most of Antarctica and warming east of the Antarctic Peninsula. This configuration is also observed in ice core records. Unforced variability and a dipole response to large volcanic eruptions contribute to weaker cooling in the Antarctic than the Arctic, consistent with the absence of a strong volcanic signal in Antarctic ice core records. The ensemble does not support a clear link between the dipole pattern and baseline shifts in the Southern Annular Mode and El Niño-Southern Oscillation proposed by some paleoclimate reconstructions. Our analysis provides a point of comparison for paleoclimate reconstructions and highlights the role of internal climate variability in driving modeled last millennium climate evolution in the Antarctic. [ABSTRACT FROM AUTHOR]

This study describes time evolution of the Southern Annular Mode (SAM) in Mid- to Late Holocene simulated with a state-of-the-art transient simulation of the last 6000 years carried out with the IPSL-CM5A2 model. Simulated SAM index exhibits significant long-term linear trends of different sign depending on the season that are closely related to multi-millennial changes in insolation which was the main driver of long-term climate change in the study period. Interactions between changes in insolation and the SAM are linked to temperature and pressure changes developed through the entire Southern Hemisphere. In fact, model results suggest that insolation changes produced significant changes in extratropical temperature gradients that, in turn, induced changes in pressure gradients synthesized by significant long-term linear trends in the SAM index from Mid- to Late-Holocene. Considering that changes in the SAM index synthetize changes in hemispheric patterns of temperature, pressure and winds, results exposed in this study should be considered as reference for reconstructions of SAM evolution in the last 6000 years from climate proxy archives. [ABSTRACT FROM AUTHOR]

While the El Niño-Southern Oscillation and Indian Summer Monsoon Rainfall (ISMR) relationship is weak in recent years, a strong correlation between May Southern Annular Mode Index (SAMI) and June–July (JJ) ISMR is a southern hemispheric source of ISMR predictability. Here, using observed and reanalysis data, we find that the SAMI–ISMR relationship is non-stationary with a potential multi-decadal variability. Both during high/low correlation periods (1980–2010)/(1949–1979), a Southern Indian Ocean Dipole (SIOD) pattern of JJ sea surface temperature anomaly is found to reverse sign during strong and weak SAMI years. The changes in the strength and location of the northern pole of SIOD during the two time blocks are consistent with corresponding changes in the cross equatorial flow and monsoon south-westerlies together with change in SAMI–ISMR correlations. Our analysis indicates teleconnection pathways through which the Atlantic Multidecadal Oscillation (AMO) may be responsible for the multi-decadal swings of SAMI–ISMR correlations through modulation of the SIOD. [ABSTRACT FROM AUTHOR]

In contrast to decreased Arctic sea ice extent, Antarctic sea ice extent shows a somewhat increased trend. There is a large interannual variability of Antarctic sea ice, especially in the Pacific sector of the Southern Ocean. The change and variability of Antarctic sea ice in synoptic timescales in the recent decades remain unclear. We identify synoptic modes of variability of Antarctic summer sea ice by applying the Self Organizing Map (SOM) technique to daily sea ice concentration data for the period 1979–2018. Nearly 40% of the variability is characterized by opposite changes between sea ice cover in the Bellingshausen, Amundsen and western Ross Seas and in the rest of the Antarctic seas, and another 30% by meridional asymmetry in the Weddell, Amundsen, and Ross Seas. Most of these spatial patterns may be explained by the dynamics and thermodynamic processes associated with anomalous atmospheric circulations related to the Southern Annular Mode (SAM) with a structure of strong zonal asymmetry. The interannual variability of the sea ice modes appears to have little connection to SAM, and only a weak relation to ENSO. The annual frequencies of SOM node occurrences also show a great decadal variability. Node 9 appears mainly prior to 1990; while node 1 occurs mainly after 1990. The decadal variability of nodes 1 and 9 is associated with the asymmetrical SAM, which results from two wavetrains excited over northern Australia and the southeastern Indian Ocean. These results further highlight the importance of understanding the role of southern mid-to-high latitude atmospheric intrinsic variability in predicting Antarctic summer sea ice variations from synoptic to decadal timescales.