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The annular structure of Antarctic oscillation (AAO) is a research hotpot, but its asymmetry receives less attention. In this paper, the self‐organizing map method is employed to cluster the AAO patterns into symmetric and asymmetric modes in austral autumn. The asymmetry is mainly reflected in the Pacific‐Atlantic sector, and the AAO evolves toward asymmetric positive polarity, with the most pronounced asymmetry in May. Originating from near Australia, the asymmetry indicates a zonal wave train in the Pacific‐Atlantic sector. Both modeled and observed results demonstrate that the sea surface temperature anomaly in the equatorial western Pacific stimulates a local meridional circulation anomaly and induces anomalous Rossby wave sources near Australia subsequently. An anomalous wave train propagating toward the Antarctic Peninsula is formed, and the associated geopotential anomaly enhances the asymmetry of AAO. Asymmetric AAO is conducive to the Antarctic dipole, which modulates the air temperature and sea ice anomalies around Antarctica. Plain Language Summary: The zonal symmetry of the Antarctic oscillation (AAO; also named southern annular mode) is well known to researchers, while the zonal asymmetry has received less attention. We use a clustering method to cluster the AAO modes in austral autumn into symmetric modes and asymmetric modes. The asymmetry of AAO is mainly reflected in the Pacific‐Atlantic sector. The results show that the AAO mode evolves to a positive asymmetric mode, and the asymmetry is most obvious in May. Both simulations and observations suggest that this asymmetry stems from sea surface temperature anomaly in the equatorial western Pacific that stimulates an anomalous local meridional circulation near Australia, and in turn triggers an anomalous wave train propagating toward the Antarctic Peninsula. The associated geopotential anomalies enhance the asymmetry of AAO. The asymmetric AAO favors the Antarctic dipole, regulating the air temperature and sea ice anomalies around Antarctica. Key Points: Via a cluster method, we obtained the zonal asymmetric Antarctic oscillation (AAO) mode, and analyzed its trend and preferred monthThe source of its asymmetry is from the sea surface temperature anomaly in the tropical western PacificThe asymmetric AAO mode has a vital influence on the Antarctic dipole [ABSTRACT FROM AUTHOR]

The diurnal cycle of precipitation and its associated land‐sea breeze circulation over coastal northern Australia are investigated using surface wind speed and enthalpy (latent and sensible heat) fluxes from the Cyclone Global Navigation Satellite System. Composite results during the austral summer of 2018–2022 show that diurnal precipitation propagates westward from the Cape York Peninsula into the Gulf of Carpentaria. The diurnal cycle of precipitation and surface wind speed are strongly coupled, with the wind speed maximum slightly leading the precipitation maximum. Additionally, analysis of the moist static energy budget shows that surface fluxes help support the westward‐propagation of diurnal precipitation. These results—based on novel satellite data and reanalysis—are consistent with previous studies that have examined the impact of the land‐sea breeze on the diurnal cycle of precipitation. The results provide a benchmark for model representation of this important atmosphere‐ocean‐land interaction. Plain Language Summary: The modulation of the diurnal cycle of precipitation over coastal northern Australia by surface winds was studied using the recently launched NASA Cyclone Global Navigation Satellite System (CYGNSS). Results show a strong connection between the daily cycles of precipitation and surface wind speed, with an offshore wind speed maximum leading the precipitation maximum by a few hours. Westward propagation of diurnal precipitation and wind speed signals occurs from the Cape York Peninsula into the Gulf of Carpentaria. A thermodynamic analysis supports the importance of the wind speed signal and associated surface fluxes for fostering offshore precipitation propagation. The novelty of this paper lies in the use of the new CYGNSS retrievals, which provide better space and time coverage of surface wind speed than previous satellite‐based measurements and are not as negatively affected by precipitation contamination. Key Points: Cyclone Global Navigation Satellite System wind speeds and latent heat fluxes are used to study the diurnal cycle over the northern Australia coastal regionEnhanced diurnal precipitation is associated with enhanced surface wind speed and convergenceDiurnal precipitation and surface wind speed signals propagate westward in tandem from the Cape York Peninsula [ABSTRACT FROM AUTHOR]

This paper presents the spatial variation of area‐orientated annual maximum daily rainfall (AMDR), represented by well‐fitted generalized extreme value (GEV) distributions, over the last century in Great Britain (GB) and Australia (AU) with respect to three spatial properties: geographic locations, sizes, and shapes of the region‐of‐interest (ROI). The results show that the spatial variation of GEV location‐scale parameters is dominated by geographic locations and area sizes. In GB, there is an eastward‐decreasing banded pattern compared with a concentrically increasing pattern from the middle to coasts in AU. The parameters tend to decrease with increased area sizes in both studied regions. Although the impact of the ROI shapes is insignificant, the round‐shaped regions usually have higher‐valued parameters than the elongated ones. These findings provide a new perspective to understand the heterogeneity of extreme rainfall distribution over space driven by the complex interactions between climate, geographical features, and the practical sampling approaches. Key Points: Rainfall series are extracted and processed from more than 11,000 regions of interest over the last 100 years in Great Britain and Australia.Spatial distribution of extreme rainfall modeled qualitatively and quantitatively shows impact from location, size, and shape of regions.Methods and findings provide new perspectives for understanding the heterogeneous nature of climate variability and climatic change impact. [ABSTRACT FROM AUTHOR]

The El Niño‐Southern Oscillation (ENSO) is considered an important driver of rainfall variability in Australia, amongst many other global locations. Despite knowledge of the expected modulation of seasonal rainfall by ENSO, there is no consistently used method to quantify the role that specific ENSO events play in driving the observed anomalous rainfall. In this manuscript we adapt the Fraction of Attributable Risk (FAR) method, commonly used to identify the anthropogenic impact on a particular event, to quantify the impact of ENSO on the occurrence of monthly rainfall anomalies. We also explicitly calculate the ENSO induced change in risk and the FAR for all observed spring rainfall rates for our eastern Australian regions. A prominent role for ENSO in driving the large spring 2022 rainfall anomalies is identified. Though we choose to focus on ENSOs impact on rainfall in various Eastern Australian regions, the results are applicable to other climate modes, regions and climatic variables. Plain Language Summary: The El Niño‐Southern Oscillation (ENSO) is considered an important driver of rainfall variability in Australia, amongst many other global locations. Despite understanding how ENSO is expected to alter rainfall, we do not currently quantify the role ENSO played in driving a observed rainfall anomaly in any given season. In this manuscript we adapt a method that is commonly used to identify the anthropogenic impact on a particular event; and instead, we quantify the impact of ENSO on the occurrence of monthly rainfall anomalies. We then calculate the ENSO‐induced change in risk for all observed spring rainfall rates for our selected eastern Australian regions. A prominent role for ENSO in driving large rainfall anomalies of spring 2022 is also identified. Though we choose to focus on ENSOs impact on rainfall in various eastern Australian regions in this study, the results are applicable to other climate modes, regions and climatic variables. Key Points: We adapt the commonly used Fraction of Attributable Risk method to attribute rainfall variability to the El Niño‐Southern OscillationWe present the ENSO induced change in risk and the FAR for all observed spring rainfall rates for three eastern Australian regionsThe increased spring 2022 East Australian rainfall was >5 times more likely, and largely attributed to the La Niña conditions present [ABSTRACT FROM AUTHOR]

We demonstrate that river discharge can be estimated by deriving water surface velocity estimates from satellite‐derived video imagery when combined with high‐resolution topography of channel geometry. Large Scale Particle Image Velocimetry (LSPIV) was used to map surface velocity from 28 s of 5 Hz satellite video acquired at a 1.2 m nominal ground spacing over the Darling River, Tilpa, Australia, during a 1‐in‐5‐year flood. We stabilized and assessed the uncertainty of the residual motion induced by the satellite platform, enhancing our sub‐pixel motion analysis, and quantified the sensitivity of image extraction rates on computed velocities. In the absence of in situ observations, LSPIV velocity estimates were validated against predictions from a calibrated 2D hydrodynamic model. Despite the confounding influence of selecting a surface velocity depth‐averaging coefficient, inference of discharge was within 0.3%–15% compared with gauging station measurements. These results provide a valuable foundation for refining satellite video LSPIV techniques. Plain Language Summary: Estimates of river flow are needed to manage water resources and flood risk. However, many of the world's rivers are not gauged, limiting hydrological understanding of river response to changing environmental conditions and storm events. We demonstrate that satellite video can be used to map velocity by tracking surface water features from one video frame to the next, and scaled to compute discharge where river geometry is known. Using a video of a flood on the River Tilpa, Australia, our results agree with ground‐based measurements to within 0.3%–15%. The ability to deploy satellites to acquire video anywhere globally could contribute to measuring discharge on ungauged rivers. Key Points: Satellite video acquired along 12.6 km of the River Darling, Australia, at 5 Hz for 28 s during a 1‐in‐5‐year storm eventSatellite video‐based velocities coupled with high resolution topography estimate riverine discharges to within 15% of in situ gauge dataParametrization of non‐contact velocimetry and choice of a depth‐averaging coefficient (α) influence the accuracy of discharge estimates [ABSTRACT FROM AUTHOR]

The diurnal cycle is often poorly reproduced in global climate model (GCM) simulations, particularly in terms of rainfall frequency and amplitude. While improvements in the regional climate model (RCM) with bias‐corrected boundaries have been reported in previous studies, they assumed that diurnal patterns are simulated correctly by the GCM, potentially leading to inaccuracies in the maximum rainfall timing and magnitude within the RCM domain. Here we provide the first examination of improvements to the diurnal cycle, within a RCM domain, achieved through the use of sophisticated bias‐corrected lateral and lower boundary conditions. Results show that the RCMs with bias‐corrected boundaries generally present improvement in capturing both rainfall timing and magnitude, particularly in northern Australia, where a strong diurnal pattern in rainfall is prevalent. We show that correcting systematic sub‐daily multivariate bias in RCM boundaries improves the diurnal rainfall cycle, which is particularly important in regions where short‐term intense precipitation occurs. Plain Language Summary: Global climate models have limitations in simulating precipitation characteristics at sub‐daily time scales, leading to significant bias in capturing rainfall timing and magnitude in regional climate model (RCM) simulations that use global climate model data as input. Previous studies have applied various bias correction approaches to the boundary conditions of RCMs, but they often assume that GCM sub‐daily rainfall patterns are simulated correctly, leading to a significant bias in maximum rainfall timing and magnitude within the domain. This study investigates the consequences of multivariate sub‐daily bias correction on the boundary conditions in order to evaluate the model performance for short‐term precipitation events. The results show that RCMs with bias‐corrected boundary conditions exhibit improvement across Australia, especially in northern Australia, which regularly experiences intense sub‐daily rainfall. Key Points: Regional climate model (RCM) with uncorrected boundaries poorly represented 3‐hourly precipitation with only 20%∼30% agreements compared to observationsSub‐daily bias correction of RCM lateral boundaries improves the sub‐daily representation of fields entering the RCM domainSub‐daily multivariate bias correction on the boundaries resulted in additional improvements, especially in northern Australia [ABSTRACT FROM AUTHOR]

Wildfires are important sources of atmospheric reactive nitrogen. The reactive nitrogen species partitioning generally depends on fire characteristics. One reactive nitrogen compound, nitrous acid (HONO), is a source of hydroxyl radicals and nitric oxide, which can impact the oxidizing capacity of the atmosphere and fire plume chemistry and composition. We study the Australian wildfire season of 2019–2020, known as Black Summer, where numerous large and intense wildfires burned throughout the continent. We use HONO and nitrogen dioxide (NO2) from the TROPOspheric Monitoring Instrument (TROPOMI) and fire radiative power (FRP) from the Visible Infrared Imaging Radiometer Suite to investigate HONO and NO2 relationships with fire characteristics. The ratio of HONO to NO2 increases linearly with FRP both in Australia and globally. Both Australian and global fire relationships depend strongly on land cover type. These relationships can be applied to emission inventories to improve wildfire emission representation in models. Plain Language Summary: During the southern hemisphere summer from 2019 to 2020, colloquially known as the Black Summer, multiple wildfires burned throughout Australia that caused widespread environmental, ecological, and property damage. The smoke and gases from the wildfires contributed to poor air quality and impacted stratospheric ozone chemistry. One gas that wildfires emit is nitrous acid, a nitrogen‐containing molecule that breaks down under sunlight to create reactive species. These reactive species undergo rapid chemical transformations that ultimately lead to the creation of pollutants, such as ozone and particulate matter. Nitrous acid is emitted alongside nitrogen dioxide from wildfire smoke, but the amounts emitted depend on fire characteristics. Multiple satellites were able to measure nitrous acid, nitrogen dioxide, and fire power during the Black Summer. By counting each smoke pixel and computing summary statistics, we found an increasing, linear relationship between the ratio of nitrous acid to nitrogen dioxide and fire power. Satellites can also characterize the type of ecosystem that is burning. With this information, we derived relationships over three ecosystem types, which can be extended globally. This relationship can be included in computer models that simulate the chemistry of the atmosphere and the impacts of wildfire emissions. Key Points: We report TROPOspheric Monitoring Instrument nitrous acid, nitrogen dioxide, and the ratio of nitrous acid to nitrogen dioxide during the Australian Black SummerMean nitrous‐acid‐to‐nitrogen‐dioxide ratio shows an increasing relationship with mean fire radiative power both in Australia and globallyThe relationship between nitrous‐acid‐to‐nitrogen‐dioxide ratio and fire radiative power is affected by vegetation type [ABSTRACT FROM AUTHOR]

For over a century, numerous proposals for increasing available water in central Australia have been raised, inspired in part by the natural occurrence of the ephemeral lake, Kati Thanda‐Lake Eyre. It has also been proposed that additional rainfall generated by the lake would spread beyond the lake itself, potentially opening up large tracts of uncultivated land to dryland agriculture. Here we use a climate model to examine how adding a permanent lake to Australia's arid center might influence local and regional precipitation. Locally, evaporative cooling from the lake increases low‐level divergence, suppressing precipitation. Regionally, additional moisture from the lake is spread thinly over the Australian continent, resulting in little change to total precipitation. Overall, our results do not support the assertion that maintaining a large inland lake like Kati Thanda‐Lake Eyre in central Australia would significantly increase precipitation, either locally or regionally. Plain Language Summary: The Bradfield water scheme proposed opening central Australia up to agriculture by diverting water inland. Supporters of the plan have argued that this might also increase rainfall. We use a climate model to simulate how precipitation would be impacted by an idealized permanent lake in central Australia. The model simulations show that the presence of a large lake has negligible impact on rainfall, both locally and regionally. Key Points: A climate model is used to test the hypothesis that creating a large lake in central Australia would increase rainfallLocally, surface cooling effects of the lake suppress the formation of precipitationRegionally, moisture from the lake is exported to other areas but the amount is small compared to natural variability in Australian rainfall [ABSTRACT FROM AUTHOR]

The cyanobacterium Trichodesmium is responsible for approximately half of the ocean's nitrogen input through nitrogen fixation. Although it was first recorded near Australia in the 18th century, the knowledge of where and when large quantity of Trichodesmium around Australia could be found is still lacking. Here, using multi‐band satellite imagery acquired between 2012 and 2021, we fill this knowledge gap through the use of deep learning, designed to recognize both the spectral shapes of individual pixels and spatial morphology of surface aggregations (scums) of Trichodesmium. Trichodesmium scums were found nearly everywhere around Australia, with a cumulative footprint (i.e., where the 10‐year average density is >0.001‰) exceeding 4.6 million km2. Strong seasonality was found, with peak months between September and November. Furthermore, temperature, iron‐rich dust and black carbon aerosols, with the latter being a result of frequent bushfires, play major roles in determining the spatial distributions and seasonality of Trichodesmium. Plain Language Summary: Responsible for half of the ocean's nitrogen input through nitrogen fixation, the saltwater cyanobacterium Trichodesmium is ubiquitous in global tropical and subtropical oceans but particularly abundant around Australia. However, although the earliest report goes back to the 18th century, the knowledge of where and when large quantities of Trichodesmium can be found around Australia is still incomplete. Based on satellite imagery and deep learning, we quantified relative abundance of Trichodesmium around Australia for the period of 2012–2021. Surface aggregations of Trichodesmium were found almost everywhere except the southern coast, with a cumulative footprint exceeding 4.6 million km2. Strong seasonality was found, with peak months between September and November. The spatial distributions and seasonality were found to correlate well with water temperature, iron‐rich dust from Australian desert, and black carbon aerosols from frequent bushfires. With the projected ocean warming in the coming century, Trichodesmium may expand further south, making the cumulative footprint even larger. Key Points: Deep learning was applied to multi‐band satellite images to detect and quantify Trichodesmium surface scums around AustraliaTrichodesmium scums were found nearly everywhere around Australia with a seasonality and a cumulative footprint exceeding 4.6 million km2Distribution and seasonality of Trichodesmium were driven by temperature, iron‐rich dust and black carbon from the mainland bushfires [ABSTRACT FROM AUTHOR]

While the pivotal role of the Indonesian Throughflow (ITF) in the global ocean circulation and climate has been widely recognized, accurate estimation of its volume transport based on observational data remains challenging. This work provides an updated estimate of the monthly ITF geostrophic transport (ITFG) in the upper 700 m at the IX1 section between Indonesia and Australia. The ITFG estimate is better constrained by improved data correction and new salinity data products. The mean ITFG of 1993–2018 is 8.2 ± 0.2 Sv, in which contributions of the temperature and salinity components (ITFT and ITFS) are 5.5 ± 0.2 and 2.8 ± 0.1 Sv, respectively. The interannual variability (∼4.4 Sv in standard deviation) is dominated by ITFT, as the result of wind‐driven thermocline dynamics, and slightly attenuated in amplitude by ITFS. The strengthening trend of 1.33 Sv decade−1 during 1993–2018 primarily arises from ITFS and secondarily from ITFT. Plain Language Summary: The Indonesian Throughflow (ITF) is of worldwide importance for the ocean circulation and climate. Existing estimates of the ITF's volume transport are subjected to uncertainties associated with data biases and simplified approaches. Here, we provide a more accurate estimate of the ITF geostrophic transport (ITFG) at the IX1 line, by adopting improved historical data correction and more realistically considering the ocean salinity effect. The IX1 line has the best and longest data coverage to represent the net transport of the upper‐layer throughflow. The mean ITFG of 0–700 m is 8.2 ± 0.2 Sv, wherein the contributions of temperature and salinity are 5.5 ± 0.2 and 2.8 ± 0.1 Sv, respectively. The ITFG variabilities on seasonal and interannual timescales are dominated by the temperature component, whereas most part of the increasing trend of 1.33 Sv decade−1 during 1993–2018 arises from the salinity component. Key Points: An updated estimate of the Indonesian Throughflow (ITF) is provided, with improvements in data correction, uncertainty estimation, and salinity effectThe ITF in the upper 700 m is of a mean geostrophic transport of 8.2 ± 0.2 Sv and interannual variability of ∼4.4 SvSalinity exerts a weak damping effect on ITF's interannual variability but fundamentally contributes to its strengthening trend since 1993 [ABSTRACT FROM AUTHOR]

Rainfall during the monsoon in northwest Australia has increased since the 1950s. Previous studies have explored possible causes of the rainfall increase; however, the trend has not been fully explained. Understanding the cause of this trend is important for interpreting climate projections and local water‐sensitive services. We explore the role of the Madden‐Julian Oscillation (MJO) in explaining the rainfall increase. The MJO, since 1974, has had a longer duration in phases associated with enhanced rainfall in northwest Australia (Phases 5 and 6) during the monsoon. We show that the rainfall trend in northwest Australia is identified only during MJO phases associated with enhanced rainfall, with a large change in daily rainfall distribution in these phases. The increasing occurrence of these MJO phases explains most of the rainfall increase, as opposed to an increase in daily rainfall independent of MJO phase, albeit with some sensitivity to MJO definition. Plain Language Summary: Rainfall during the monsoon in northwest Australia has been increasing since the 1950s. In this study, we explore if a semi‐periodic pulse of rainfall and clouds near the equator, known as the Madden‐Julian Oscillation (MJO), may be related to the increased rainfall in the northwest. This pulse of clouds has been found, since 1974, to be spending longer periods of time over northwest Australia. We observed that the increase in MJO duration over northern Australia leads to increasing rainfall in northwest Australia. Key Points: Rainfall in northwest Australia has been increasing since the 1950s, and the cause of this trend has so far remained unexplainedThe Madden‐Julian Oscillation (MJO) has also been increasingly occurring in phases associated with increased rainfall over northern AustraliaThe increase in MJO convective phases over northern Australia explains most of the increase in rainfall since 1974 in northwest Australia [ABSTRACT FROM AUTHOR]

A new inter‐basin teleconnection analysis method is proposed to comprehensively investigate the connection among global oceans. The strong negative correlation (−0.59) between sea surface temperature (SST) along Leeuwin Current (LC) and East Australia Current (EAC) is discovered and named as Australia Boundary Current Dipole (ABCD). This new inter‐basin air‐sea coupled mode exhibits remarkable interannual variability, with a peak phase in austral summer. The related SST anomalies are mainly generated by anomalous Australia High induced opposite alongshore surface winds to enhance/suppress the heat transport of the two warm currents, in turn, reinforce the wind anomalies by heating/cooling the overlying atmosphere and changing regional pressure anomalies. The meridional ocean advections control the anomalous SST, indicating the essential role of coastal Bjerknes feedback. The kinetic energy analysis further demonstrates that ABCD represents the reverse variation pattern of LC and EAC. Plain Language Summary: The interactions between different oceans have strong impact on the global climate change. We proposed a new method aims to reveal global oceans interactions and thus discovered the opposite change features between the sea surface temperature (SST) off the west and east coasts of Australia. The coastal SST anomalies are accompanied by the synchronous evolution of alongshore surface winds, coastal boundary currents, and sea level pressure, demonstrating it as an intervein climate pattern and we name it as Australia Boundary Current Dipole (ABCD). The anomalous Australia High, evaporation anomalies and the heat transport of Leeuwin Current (LC) and East Australia Current (EAC) contribute to the evolution of ABCD. ABCD also indicates reverse variability of LC and EAC. Our results reveal the existence and generation mechanism of ABCD for the first time, which advances our knowledge of air‐sea interactions and may provide new insights into the research of marine ecology. Key Points: A new method is proposed to reveal inter‐basin teleconnectionA new inter‐basin climate pattern between Indian and Pacific Oceans is discovered and named Australia Boundary Current Dipole (ABCD)ABCD represents the reverse variability feature of Leeuwin Current and East Australia Current [ABSTRACT FROM AUTHOR]

Accurate chronology of climatic shifts is critical to understand the controls on landscape and species evolution. Unfortunately, direct dating of continental climate change is hindered by the scarcity of dateable terrestrial products evidencing climatic shifts. Here we use ferruginous indurations from the arid landscapes of the Nullarbor Plain in southern Australia to constrain the timing of Plio‐Pleistocene aridification in the continental realm. We present (U‐Th)/He goethite data implying active induration processes between c. 2.7 and 2.4 Ma. Chemical‐mineralogical and petrographic examination suggests that formation of ferruginous indurations was linked with a decline of the groundwater table, driven by the rapid climatic shift from humid late Pliocene to arid early Pleistocene conditions. Combined with local to global climatic proxies, we conclude that ferruginous indurations are promising targets to obtain absolute ages on landscape evolution to refine continental climatic chronology and improve understanding of the environmental drivers of species diversification and extinction. Plain Language Summary: The reconstruction of Earth's climate record is typically founded on the physicochemical properties of marine sediments. Continental sediments that yield time‐constrained climate information are rare, but important to interpret wider Earth system responses and the co‐evolution of regional climate, landscape, and biota. This study presents direct dating of continental climate change on the Nullarbor Plain to constrain its development as an important biogeographic barrier driving species diversification between SW‐ and SE‐Australia. Age dating of iron‐oxide cements constrains the waning availability of mobile water (e.g., groundwater) and the onset of drier conditions related to global Plio‐Pleistocene climate change. These findings demonstrate that iron‐oxides may provide an excellent continental archive to anchor major climate shifts and help understand associated terrestrial ecosystem change. Key Points: (U‐Th)/He data from ferruginous indurations capture the onset of Plio‐Pleistocene aridification in southern AustraliaCorrelation of induration age with other climatic proxies indicates that ferruginous indurations track terrestrial water table evolutionTiming of aridification constrains evolution of important biogeographic barrier [ABSTRACT FROM AUTHOR]

Coarse resolution datasets often poorly capture precipitation properties. It is commonly expected that skill at the local level should increase by refining spatial resolution. Here, we examine the influence of spatial resolution on the accuracy of means and extremes in precipitation by comparing high‐resolution dynamically downscaled data against the driving lower‐resolution reanalysis. We show that the higher‐resolution data are less accurate than lower‐resolution data for both mean and extreme precipitation. The quantitative deterioration (increase in the domain averaged relative error) from coarse to high resolution varies typically between 1%–8% and 5%–30% for mean and extreme precipitation, respectively. We also find that the finer‐scale variability resolved only by the higher‐resolution system and successfully predicted by that system is of negligible magnitude compared to the overall error (less than 1%). We conclude that finer‐scale resolution by itself does not necessarily bring a meaningful improvement in local simulation accuracy. Plain Language Summary: In this study, we examined the impact of spatial resolution on means and extremes in precipitation using high‐resolution dynamically downscaled data against the driving lower‐resolution reanalysis over Australia. We report that high‐resolution data are less accurate than lower resolution data for standard statistics of precipitation. We also discuss the possible reasons for the deterioration and variations between previous studies. The results highlight that increasing the horizontal resolution alone will not help address problems with precipitation. Significant model developments and data assimilation techniques are required to reap the benefits of high horizontal resolution. Key Points: Increasing the horizontal resolution alone did not help address problems with simulating regional precipitation in this case studySignificant model developments are required to reap the benefits of high horizontal resolution [ABSTRACT FROM AUTHOR]

The kinematics of the Paleoproterozoic assembly of Earth's first supercontinent, Nuna, are still debated. We present new paleomagnetic results from two Paleoproterozoic rock formations in the North Australia Craton (NAC) that exemplify cratonic assembly processes in the leadup to Nuna formation. Our new paleomagnetic data for the 1,825 Ma Plum Tree Creek Volcanics of the proto‐NAC and the layered mafic‐ultramafic 1,855 Ma Toby intrusion of the Kimberley Craton suggest their amalgamation just prior to ca. 1.8 Ga through a scissor‐like ocean closure to form the NAC, in accord with geological records. Comparing these new results with extant poles from Australia and other major cratons suggests similarly minor relative plate motions between ca. 1.9 and 1.65 Ga during craton and supercontinent formation. A global reconstruction suggests that these events could be related to a major slab‐suction event leading to Nuna formation. Plain Language Summary: Earth's evolution is characterized by the recurring assembly of most tectonic plates into one single supercontinent. There is mounting evidence that at least three supercontinents existed throughout Earth history. This cycle of supercontinents potentially played an important role for the evolution of life and is inextricably connected to plate tectonics. However, we still don't understand how and when exactly the supercontinent cycle initiated. We present here new paleomagnetic data allowing us the most precise paleogeographic reconstruction for the time interval before the first of the three known supercontinents formed. Our data reveals a small‐scale collisional assembly of the Australian cratons in the vicinity of the formation of other major cratons at that time. Our global reconstruction using the most up to date paleomagnetic data set can be interpreted as evidence for a model where all cratons formed over a mantle downwelling structure that ultimately lead to the initiation of the supercontinent cycle. Key Points: Two new high‐quality Paleoproterozoic paleopoles for the North Australian Craton are presentedThe new paleomagnetic data suggest a scissor‐like assembly of the North Australian CratonOur new kinematic model proposes a situation prior to the formation of the first supercontinent related to a major slab‐suction event [ABSTRACT FROM AUTHOR]

Australia experienced record‐breaking wildfires during 2019–2020, which emitted large amounts of carbonaceous aerosols (CAs) to the atmosphere. In this study, we explored the atmospheric dynamics and thermodynamic mechanism of the long‐range transport of CAs during November 2019–February 2020. The results indicate that the emitted CAs had a ternary advective spreading pattern across the Pacific Ocean in the Southern Hemisphere (SH), influenced mainly by the westerlies and anticyclonic systems. Upward vertical motion over the convergence zone and heat released from smoke pyro‐cumulonimbus clouds and strong light absorption of CAs provided strong vertical lift as the predominant injection pathway of the CAs into the stratosphere in the central Pacific Ocean in the SH. The abundant tropospheric CAs induced atmospheric heating (and potentially surface cooling), with increasing air temperature and decreasing of surface temperature. The anomalous thermal structure led to changes in atmospheric circulation, which weakened the upward vertical motion. Plain Language Summary: During the summer of 2019–2020, Australia suffered unprecedented wildfires. These wildfires emitted large amounts of pollutants into the free atmosphere. The pollutants are mainly composed of carbonaceous aerosols (CAs). Under the effects of meteorological conditions, the CAs experienced a long‐range spread expanding from the western Pacific Ocean to the eastern Pacific Ocean even arriving at the Atlantic Ocean. During the transportation, the CAs were accumulated over the central Pacific Ocean under the trapping effect of the anticyclone and then exhibited significant lift owing to upward motion over the convergence zone between westerlies and anticyclone and heat buoyancy released from smoke pyro‐cumulonimbus clouds and strong light absorption of CAs. As a response, the strong absorption of CAs resulted in the warming of the atmosphere and cooling of the surface, which enhanced atmospheric stratification and constrained the development of atmospheric instability. Thus, the upward vertical motion was weakened. Key Points: The westerlies and anticyclonic system dominated the advective spread of carbonaceous aerosols (CAs)The upward vertical motion, heat released from smoke pyro‐cumulonimbus clouds, and strong CAs light absorption contributed to CAs liftThe CAs caused warming of air temperature and cooling of surface temperature, which weakened the upward vertical motion [ABSTRACT FROM AUTHOR]

A decadal variability is revealed in sea surface temperature (SST) wavenumber‐4 (W4) pattern of southern subtropics (20°–55°S) using wavelet and empirical orthogonal function analysis. The decadal variability of the SST W4 pattern evolves from the decadal modulation of the South Pacific Meridional Mode (SPMM) as seen in SST footprints. The SST residuals of the SPMM create a favorable environment for the frequent occurrence of positive/negative type of the SST W4 pattern and is discussed. Since SST W4 pattern covers the globe, it potentially affects the decadal rainfall variability over Southern continents by modulating local atmospheric circulation. During positive phase, anomalous SST close to South America, Australia, and Southern Africa enforces the wind to go on/offshore and converges/diverges the moisture into/out of the landmass. As a result, specific humidity changes and alters the rainfall over Southern continents on a decadal scale. The scenario is opposite during the negative phase. Plain Language Summary: The sea surface temperature (SST) has four positive (negative) loading centers located in the South‐central Pacific, South‐western Atlantic, South‐western Indian Ocean, and South of Australia (South‐eastern Pacific, South‐eastern Atlantic, South‐eastern Indian Ocean, and South‐western Pacific Ocean), called a wavenumber‐4 (W4) pattern in the southern subtropics. It is generated due to a coupling with a similar W4 pattern seen in the atmosphere. Apart from year‐to‐year variation, this W4 pattern also has a decadal cycle and is reported in this study. The reason behind this is mainly linked to the decadal variation of the South Pacific Meridional Mode (SPMM). When the SPMM decays, it leaves some SST signals over the South Pacific Ocean which remain for a longer time and lead to SST W4 having more positive/negative events in one decade compared to others. The resulted SST W4 pattern affects the Southern continental rainfall by controlling the local atmospheric circulation. Key Points: Decadal variability in sea surface temperature (SST) wavenumber‐4 (W4) pattern is revealed over southern subtropics (20°–55°S)The footprinting mechanism and SST residuals from the South Pacific Meridional Mode lead the SST W4 decadal variability by 2 yearsSST W4 potentially affects the decadal rainfall variability over Southern continents by modulating local atmospheric circulation [ABSTRACT FROM AUTHOR]

The Nullarbor Plain is underlain by thick cratonic lithospheric mantle that is almost devoid of contemporary seismicity. Analysis of high‐resolution digital elevation models indicates neotectonic fault‐propagation fold traces on the nearly flat karst landscape that locally extend to lengths of >100 km, suggesting potential for hosting large (>7.3–7.5) moment magnitude earthquakes. Along‐strike maximum displacements are not proportional to neotectonic fold surface trace length but are spatially associated with crust‐scale electrical conductors identified in magnetotelluric surveys. Two major conductors penetrate from the upper crust to the uppermost mantle (at depths < 60 km) along crustal scale shear zones. Conductivity in the uppermost mantle shear zones is higher than conductivity at increased depth, suggesting fluid‐enhanced enrichment with hydrogen and/or carbon. Lithospheric fluid localization associated with ancient slab subduction and/or hydrothermal alteration may have weakened pre‐existing faults and enhanced neotectonic faulting in the Nullarbor Plain. Plain Language Summary: Stable cratons on the Earth are generally considered to be immune from large earthquakes. Historical seismic quiescence and a paucity of evidence for geologically recent activity on large intraplate faults can result in an absence or low level of seismic hazard awareness, though intraplate earthquakes have caused more fatalities than interplate earthquakes. Long recurrence intervals commonly obscure evidence for paleo‐earthquakes because surface erosional processes may erode or bury surface ruptures and other neotectonic deformational features. Finding an ideal place that can provide sufficient observations of intracontinental active faults is challenging but pivotal for unraveling intracontinental fault dynamics and seismic hazard assessment. The nearly flat Nullarbor Plain in South‐Central Australia is covered by 100s‐m‐thick limestone, which is cut by reactivated reverse faults propagating upward from the Precambrian basement. The limestone has been exposed to the surface since the mid‐Miocene. The arid climate in this region has helped preserve these neotectonic features from surface erosion. Fault traces with high displacements can be well correlated with patches with high electrical conductivities, which are sensitive to fluids in the lithosphere. With co‐located seismic reflection profiles, gravity, and magnetic maps, we propose that enhanced neotectonic activity is associated with fluids ascending from deeper parts of the lithosphere. Key Points: The Nullarbor Plain in Australia is a cratonic region with neotectonic fault (fold) traces of 7–150 km lengthFault displacement is not positively related to fault length but is spatially linked to high electrical conductors in the lithosphereLithospheric fluid localization is proposed to have weakened pre‐existing faults and enhanced neotectonic faulting in the Nullarbor Plain [ABSTRACT FROM AUTHOR]

The latter months of 2020 and 2021 were marked by two of the largest Antarctic ozone holes on record. That such large ozone holes occurred despite ongoing ozone recovery raises questions about their origins and climate impacts. Here we provide novel evidence that supports the hypothesis that the ozone holes were influenced by two distinct and extraordinary events: the Australian wildfires of early 2020 and the eruption of La Soufriere in 2021. We further reveal that both ozone holes were associated with widespread changes in Southern Hemisphere climate that are consistent with the established climate impacts of Antarctic ozone depletion, including a strengthening of the polar stratospheric vortex, enhanced surface westerlies over the Southern Ocean, and surface temperature changes over Antarctica and Australia. The results thus provide suggestive evidence that injections of both wildfire smoke and volcanic emissions into the stratosphere can lead to hemispheric‐scale changes in surface climate. Plain Language Summary: The Antarctic ozone hole is characterized by dramatic decreases in stratospheric ozone during the austral spring months. The ozone hole is expected to recover over the next few decades in response to the phasing out of ozone‐depleting substances. However, the latter months of 2020 and 2021 were marked by two of the largest Antarctic ozone holes on record, which raises questions about their origins and climate impacts. Here we provide novel evidence that supports the hypothesis that the ozone holes were influenced by two extraordinary events: the Australian wildfires of early 2020 and the eruption of La Soufriere in 2021. We further reveal that both ozone holes were associated with changes in Southern Hemisphere surface climate consistent with the established climate impacts of Antarctic ozone depletion. Together, the results provide suggestive evidence that injections of both wildfire smoke and volcanic emissions into the stratosphere can lead to hemispheric‐scale changes in surface climate. Key Points: The large Antarctic ozone holes of 2020 and 2021 were accompanied by stratospheric burdens of wildfire and volcanic emissions, respectivelyBoth ozone holes were associated with pronounced changes in surface climate consistent with the impacts of Antarctic ozone depletionTogether, the linkages suggest that both wildfire smoke and volcanic emissions can lead to large‐scale changes in surface climate [ABSTRACT FROM AUTHOR]

Oceanic anoxic event 1d (OAE 1d) has been well studied at northern low latitudes (i.e., in Tethys and the North Atlantic); however, the paleoenvironmental response to this event at high latitudes has not been documented and the triggering mechanism remains unknown. Here, we address both of these shortcomings by presenting the first detailed sedimentary and multi‐proxy geochemical record of the OAE 1d at southern high latitudes (60–62°S), obtained from sediments using Site U1513, IODP Expedition 369. Biostratigraphic and chemostratigraphic data support correlation of the interval studied with OAE 1d, and the sedimentary mercury proxy reveals that at least at Site U1513, OAE 1d is associated with the Central Kerguelen large igneous province volcanism. Furthermore, the significant increase in continental runoff and consequent terrigenous input from southwestern Australia in the southeastern proto‐India Ocean might have resulted in regionally weakened bottom‐water oxygenation and strengthened organic matter burial during OAE 1d. Plain Language Summary: Geological marine records hold valuable information that could inform predictions for the future of our warming world. Marine sediments are an important reservoir of the global organic carbon and changes at the seafloor can modulate release of CO2 into the atmosphere. Cretaceous oceanic anoxic event 1d (∼latest Albian) was a significant disturbance to the global carbon cycle in the mid‐Cretaceous although it is poorly documented in the southern hemisphere especially at high latitudes. Our integrative sedimentary‐geochemical study demonstrates that oceanic anoxic event 1d at southern high latitudes might have been directly triggered by Central Kerguelen large igneous province volcanism. Volcanic emissions are proposed to have shifted the climate such that runoff and input of terrigenous sediment from southwestern Australia increased. These changes would have weakened bottom‐water oxygenation and increased organic matter burial in the southeastern proto‐Indian Ocean. Key Points: We present the first sedimentary and geochemical records for oceanic anoxic event 1d at southern high latitudes (60–62°S)Environmental changes during oceanic anoxic event 1d might be directly triggered by Central Kerguelen large igneous province volcanismMultiple paleoenvironmental changes occurred in the study area during oceanic anoxic event 1d [ABSTRACT FROM AUTHOR]

The 2019/2020 Australian New Year's wildfires injected record amounts of smoke and biomass burning products into the lower stratosphere. The Aura Microwave Limb Sounder (MLS) tracked the evolution of distinct plumes of fire–influenced air as they rapidly spiraled up to the mid–stratosphere. In the months following the fires, smoke spread throughout the Southern Hemisphere (SH) stratosphere. We contrast the evolution of the SH midlatitude lower stratosphere in 2020 with the 17–year MLS record. Long after the coherent plumes dispersed, data from MLS and other satellite instruments show unprecedented persistent and pervasive depletion in HCl (50%–60% below climatology) and enhancements in ClO and ClONO2 that were not transport related; peak anomalies occurred in mid–2020. We conclude that the observed perturbations likely arose from heterogeneous chlorine activation on widespread smoke particles. The sustained chlorine activation was far weaker than in typical winter polar vortices, inducing at most minor changes in ozone. Plain Language Summary: In late December 2019/early January 2020, during the Black Summer fire season in Australia, an intense outbreak of a number of fire–induced and smoke–infused thunderstorms occurred, collectively known as the Australian New Year's event. Multiple plumes of polluted air were rapidly lofted from the surface and deposited in the lower stratosphere (above 14 km altitude). The largest of the plumes of biomass burning pollutants were tracked by the Microwave Limb Sounder (MLS) on NASA's Aura satellite for several months as they circled the globe. In addition to those distinct confined plumes, smoke from the fires permeated the Southern Hemisphere (SH) lower stratosphere. Well after the discrete plumes dispersed, MLS and other satellite instruments observed widespread and long–lasting perturbations in the composition of the SH midlatitude lower stratosphere. In particular, unprecedented depletion in the main stratospheric chlorine reservoir species (HCl) was accompanied by enhancements in another chlorine reservoir (ClONO2) as well as the ozone–destroying form of chlorine (ClO), with maximum departures from average measured in mid–2020. These anomalous signatures likely arose from chemical processing on smoke particles. The enhancement in the ozone–destroying form of chlorine, far weaker than that in winter polar regions, had only minor effects on ozone. Key Points: Satellite data show strongly depleted HCl and enhanced ClO and ClONO2 in the southern midlatitude lower stratosphere through much of 2020The unprecedented midlatitude chlorine repartitioning likely arose from heterogeneous activation on widespread Australian wildfire smokeThe sustained midlatitude chlorine activation was far weaker than in typical winter polar vortices, inducing at most minor changes in ozone [ABSTRACT FROM AUTHOR]

This study presents the conjugate ionospheric disturbances triggered by the 2011 Tohoku‐Oki reflected tsunami oceanic waves using the ground‐based Global Navigation Satellite System (GNSS) total electron content (TEC) observations. We found that the equatorward and westward propagating nighttime medium‐scale traveling ionospheric disturbances (MSTIDs) occurred over Japan and Australia simultaneously following the tsunami oceanic waves reflected by the Emperor Seamount Chain in the northern hemisphere. The atmospheric gravity waves driven by reflected tsunami oceanic waves are hypothesized to be the source to trigger the conjugate MSTIDs by transporting the polarization electric fields along the field line to the conjugate hemisphere. Moreover, only the southwestward propagating MSTIDs have this conjugate effect, which could be due to the wavefront orientation. The Perkins instability could also be involved in the interhemispheric coupling process. This study provides the first observational evidence that the reflected tsunami can induce conjugate ionospheric disturbances through electrodynamic forcing. Plain Language Summary: The 2011 M 9.1 Tohoku‐Oki earthquake occurred near the east coast of Honshu, Japan, unleashing a savage tsunami traveling across the Pacific Ocean and beyond. Some tsunami oceanic waves were reflected by seafloor topography in the Pacific Ocean, thus propagating backward toward Japan. These reflected tsunami oceanic waves also excited gravity waves propagating upward into the upper atmosphere, causing plasma perturbations at the atmosphere‐space interaction region above Japan. Gravity wave‐driven variations in the neutral wind can move the plasma against the Earth's magnetic field lines, thus generating currents and electric fields. Since the Earth's magnetic field lines are conductive like electric power lines, the generated electric fields can transport along the magnetic field line from Japan to the southern hemisphere, causing plasma disturbances above Australia. This study provides observational evidence that the localized tsunami can also cause space plasma perturbations in the conjugate area. Key Points: Conjugate ionospheric disturbances associated with the 2011 Tohoku reflected tsunami‐driven gravity waves are observed for the first timeReflected tsunami‐driven gravity waves cause the conjugate ionospheric disturbances through polarization electric fieldsResulting conjugate ionospheric effect depends on the propagation direction of gravity waves [ABSTRACT FROM AUTHOR]

During March 2021, large regions of Eastern Australia experienced prolonged heavy rainfall and extensive flooding. The maximum daily mean column integrated water vapor transport (IVT) over Sydney during this event was within the top 0.3% of all days since 1980, and the 10‐day mean IVT was in the top 0.2%. In this study, we have examined the change in frequency of extreme IVT events over Sydney in 16 climate models from the Coupled Model Intercomparison Project 6 under two Shared Socioeconomic Pathways (SSP245 and SSP585). Generalized Extreme Value modeling was used to further analyze the change in frequency of extreme IVT events. We found the probability of long duration high IVT events is projected to increase by 80% at the end of the century, but the future change in IVT is correlated to the rate of global and regional warming in each model. Plain Language Summary: During March 2021, large regions of Eastern Australia experienced prolonged heavy rainfall and extensive flooding. This was associated with strong horizontal water vapor transport over this region that persisted for approximately 10 days. The amount of water vapor transported over Sydney during this event was extreme and within the top 0.3% of all days since 1980. In this study, we used climate models to project how much more often events such as these may occur by the end of the twenty‐first century under two greenhouse gas emission scenarios. We found that the probability of long duration high water vapor transport over Sydney, as in March 2021, may increase by 80%. Key Points: Sydney's March 2021 floods were associated with persistent high water vapor transportThe probability of long‐duration high integrated water vapor transport events should increase by the end of the twenty‐first centuryDifferences in climate sensitivity within the CMIP6 ensemble may increase the spread of moisture flux projections [ABSTRACT FROM AUTHOR]

This study provides a Miocene‐to‐recent history of Tasman Leakage (TL), driving surface‐to‐intermediate waters from the Pacific into the Indian Ocean. TL, in addition to Indonesian ThroughFlow (ITF), constitutes an important part of the Southern Hemisphere Supergyre. Here, we employ deep‐sea benthic δ13C timeseries from the southwestern Pacific and eastern Indian Oceans to identify the history of Tasman Leakage. The δ13C results combined with sedimentary evidence show that an inter‐ocean connection south of Australia existed from 7 Ma onward. A southward shift in Westerlies combined with a northward movement of Australia created the oceanic corridor necessary for Tasman Leakage (between Australia and the sub‐Antarctic Front) at this time. Furthermore, changes in the northern limb of the Supergyre (ITF) are evident in the sedimentary record on Broken Ridge from ∼3 to 2 Ma when Banda Sea intermediate waters started originating from the North Pacific. Plain Language Summary: Global ocean circulation allows for the distribution of heat between different latitudes and different water depths. It has long been understood that much of the return flow from the Pacific to the Atlantic occurs through the Indonesian Throughflow, but more recently, oceanographers have identified another, deeper pathway south of Australia: the Tasman Leakage. This connection consists of Pacific waters that leave the Tasman Sea by flowing southwest around Australia, into the Indian Ocean and ultimately back into the Atlantic. We use carbon isotopes of benthic foraminifera, coupled with sedimentation patterns around Australia and the Indian Ocean, to determine the onset of this new pathway in global thermohaline circulation: This occurred around 7 Ma. This onset was coincident with major global climatic and oceanographic change and was controlled by the position of the Australian continent and the sub‐Antarctic Front. TL onset was only able to occur when Australia had moved far enough north to allow for westward flow. Key Points: Benthic δ13C time‐series from the southwestern Pacific and eastern Indian Ocean suggest onset of Tasman Leakage at 7 MaLatitudinal movement of the Australian continent away from the sub‐Antarctic Front creates the oceanic corridor necessary for Tasman LeakageThe Late Miocene onset of Tasman Leakage completed the Southern Hemisphere Supergyre and ushered in the near‐modern ocean circulation style [ABSTRACT FROM AUTHOR]

Sea surface height (SSH) along the west coast of Australia is key to local climate and is strongly forced by remote surface wind variability related to El Niño Southern Oscillation (ENSO) in the tropical Pacific Ocean. This study provides a method to predict interannual variability in SSH along the west coast of Australia using a simple 1.5‐layer dynamical ocean model forced by a statistical atmospheric model for ENSO‐related winds. The model has realistic coastlines and is driven by reanalysis surface winds regressed onto an ENSO index. The model when run in hindcast mode to predict past variability can simulate tide gauge observations at Fremantle along the west coast of Australia up to 13 months in advance, which outperforms persistence. We conclude that this methodology can be useful as a baseline for gauging the performance of more sophisticated forecast models for predicting SSH variations along the west coast of Australia. Plain Language Summary: Sea surface height (SSH) along the west coast of Australia is key to regional climate and is strongly forced by remote surface wind variability related to El Niño Southern Oscillation (ENSO) in the tropical Pacific Ocean. Previous studies predicted interannual variability in SSH in this region using sophisticated ocean‐atmosphere coupled general circulation models, but their ocean models had coarse horizontal resolution, required to reduce computational burden. This study provides a much simpler method to predict SSH variability along the west coast of Australia using a simple ocean dynamical model with realistic coastlines forced by ENSO‐related atmospheric winds. Our model, run in hindcast mode to predict past SSH variability, is able to simulate SSH anomalies along the west coast of Australia up to 13 months in advance. A true forecast system to predict future variations would also require prediction of ENSO. However, this methodology can be useful as a baseline for gauging the performance of more sophisticated model forecast systems. Key Points: Interannual variability in sea level along the west Australian coast can be predicted up to 13 months in advance using a simple ocean modelTo illustrate, the model is run in hindcast mode forced remotely by Pacific surface winds related to El Niño Southern OscillationModel hindcasts generally outperform persistence forecasts in terms of anomaly correlation and root‐mean‐squared differences [ABSTRACT FROM AUTHOR]

Using continuous data from a dense seismic array in Southwestern China, we tracked S‐wave microseism sources generated by two storms in Southeast Australia and the North Atlantic. In the frequency band 0.1–0.2 Hz, the beam strengths for SV‐ and SH‐wave sources can reach 29% and 18% of P‐wave, respectively. We found that the strong SH‐wave is only observed when the seismic sources are near the thick sedimentary regions whereas P‐ and SV‐wave is irrespective of that. It appears that in addition to a three‐dimensional structure that is needed for conversion from P‐wave to SH‐wave, amplitude enhancement by a sedimentary layer is essential for the detection of SH‐wave. Plain Language Summary: The interactions of ocean waves in the opposite propagation directions generate an equivalent vertical force in the ocean, creating dominant seismic noise in the frequency band 0.1–0.3 Hz. This forcing mechanism can explain the observations of P or Rayleigh waves but cannot explain the observations of SH or Love waves. In this study, from precise locations of SH‐wave sources in Southeast Australia and the North Atlantic, it is shown that SH‐wave sources are only found near a region of the thick sedimentary layer at the sea bottom. Amplification of waves in a thick sedimentary layer seems to be required to excite observable SH‐wave in seismic noise. Key Points: A large, dense seismic array in Southwestern China detects clean S‐wave signals in seismic noiseStrong S‐wave signals were tracked for the storms in Southeast Australia and the North AtlanticThe SH‐wave sources were only observed near thick sediment at the sea bottom, suggesting an amplitude enhancement by sediment is essential [ABSTRACT FROM AUTHOR]

Australia suffered a long‐lasting extensive drought in 2019 with catastrophic wildfires creating about $4.4 billion damages, the worst record in the recent four decades. Concurrent with this extreme drought, the tropical Indo‐Pacific oceans exhibited an extraordinary combination of sea surface temperature (SST) anomalies, characterized by a Central‐Pacific (CP) El Niño event with westernmost location and the third strongest positive Indian Ocean Dipole (IOD) event. We here show evidence that this unique combination was responsible for the pan‐Australian drought as a westward located CP El Niño event and a strong positive IOD event can exacerbate precipitation reduction in northeastern and southern Australia, respectively. These continent‐wide extreme droughts could become more frequent over Australia in a warming world, considering projected increases in both CP El Niño and extreme positive IOD events superimposed on secular warming and drying trends. Plain Language Summary: Australia is the driest inhabited continent in the world, 70% of which is either arid or semiarid land. During 2019, Australia was ravaged by the worst drought in decades with devastating wildfires destroying around 3,000 homes and affecting about one billion animals. The physical mechanisms driving this extreme drought remains unclear. Concurrent with this long‐lasting continent‐wide drought, the Indo‐Pacific oceans showed pronounced sea surface temperature anomalies associated with a record westernmost‐located Central Pacific (CP) El Niño event and the third strongest Indian Ocean Dipole (IOD) event co‐occurring. Our observational diagnostics and numerical model experiments show that these two compounding events caused atmospheric circulation anomalies that were responsible for the extreme precipitation deficiencies over Australia. With global warming, both CP El Niño and extreme positive IOD events are projected to become more frequent, which hints to increased risk of the severe Australian droughts in the future. Key Points: Australia suffered a long‐lasting extensive drought in 2019, the worst record in the recent four decadesThis extreme drought can be well explained by combined effects of the westernmost‐located CP El Niño and third strongest positive Indian Ocean Dipole (IOD) eventsSevere Australian droughts could occur more frequently in a warming world with projected increases in both CP El Niño and extreme IOD events [ABSTRACT FROM AUTHOR]

The Great Serpentinite Belt of eastern Australia is a ∼1500 km long dismembered ophiolite assumed to be Cambrian based on studies of small (typically <50 m2) exotic meta‐igneous inclusions despite contrasting ages (Cambrian—Devonian) and complex P‐T histories. To overcome these issues, we studied a ∼18 km2 coherent block of dismembered ophiolite that provides robust geological context to sampling the ophiolite. Zircon U‐Pb‐Hf‐O isotope and trace analyses from three plagiogranite dykes cutting massive gabbro confirm ∼283–277 Ma ages and a mantle source. As a result, we argue older Cambrian to Devonian plagiogranite and subducted blocks were inherited from previous subduction events in eastern Australia. These findings allow us to match the Great Serpentinite Belt with the contemporary Dun Mountain ophiolite (New Zealand) and the Koh ophiolite (New Caledonia), thus supporting a new, integrated Pacific Gondwana margin paleogeography involving multiple arcs and subduction zones. Plain Language Summary: Ophiolites are fragments of oceanic crust and mantle that have been thrusted onto continents by tectonics. Ophiolites provide important records of oceanic lithosphere and for assessing the timing of significant tectonic events. Previous studies of the Great Serpentinite Belt of eastern Australia, established a ∼530 Myr age. However, studies focused on small (typically < 50 m2) exotic fault bounded blocks of ophiolitic material of varying geological ages and complex metamorphic histories. By focusing on an intact 18 km2 fragment of oceanic crust with reliable geological relationships and low degrees of metamorphism, our results show this ophiolite is far younger (∼280 Myr old). This age overlaps with ophiolites in New Caledonia and New Zealand on what was the paleo‐Pacific Gondwana margin. This new discovery leads to a new paleogeography for this period and improves geological links between eastern Australia, New Zealand, and New Caledonia. Key Points: A coherent 18 km2 ophiolite block within the Great Serpentinite Belt, eastern Australia is Early Permian in ageCambrian to Ordovician ophiolite inclusions (often <50 m2) do not date the main ophiolite but are inherited from previous subduction eventsA new reconstruction of the Early Permian east Gondwana paleogeography that incorporates coeval ophiolites in New Zealand and New Caledonia [ABSTRACT FROM AUTHOR]

The strongest and most persistent upward propagation of zonal wavenumber 1 (WN1) Rossby waves from the troposphere on record led to the rare Antarctic sudden stratospheric warming (SSW) in September 2019. The dynamical contribution from instantaneous anomalous WN1 and its linear interference with the climatological WN1 contributed equally to the event. The unprecedented WN1 planetary wave behavior is further attributed to a long‐lived midlatitude circumpolar Rossby wave train in the troposphere that was sustained by anomalous convection, first over the subtropical Pacific Ocean east of Australia and then over the eastern South Pacific. Besides the tropospheric wave forcing, the phase of the quasi‐biennial oscillation in the upper stratosphere also facilitated the weakening of polar vortex. Moreover, this SSW strongly influenced the tropospheric circulation via the Southern annular mode, favoring conditions linked to the 2019 bushfires in eastern Australia. Plain Language Summary: A sudden stratospheric warming (SSW) is an extreme event associated with rapid warming high up in the stratosphere, which can influence weather conditions at the surface. In September 2019, a rare strong SSW occurred in the Southern Hemisphere, providing further insight into these events. Here, we show that this SSW was caused by exceptionally strong and long‐lasting atmospheric waves propagating upward from the troposphere into the stratosphere. Anomalous tropical convection is a possible source for these large‐scale atmospheric waves. Besides, the zonal winds in the tropical upper stratosphere set a favorable background condition for the occurrence of the SSW. Our results also link the SSW to subsequent anomalous tropospheric circulation and the late 2019 bushfires in eastern Australia. Key Points: Both the linear and nonlinear contributions of anomalous wavenumber 1 led to the Antarctic sudden stratospheric warming in September 2019The wave source of this unusual wave activity can be traced back to persistent anomalous convection over the South PacificThe easterly phase of the quasi‐biennial oscillation in the upper stratosphere sets a favorable mean state [ABSTRACT FROM AUTHOR]

The 2019 positive Indian Ocean Dipole (IOD) was the strongest event since the 1960s which developed independently without coinciding El Niño. The dynamics is not fully understood. Here we show that in March–May, westward propagating oceanic Rossby waves, a remnant consequence of the weak 2018 Pacific warm condition, led to anomalous sea surface temperature warming in the southwest tropical Indian Ocean (TIO), inducing deep convection and anomalous easterly winds along the equator, which triggered the initial cooling in the east. In June–August, the easterly wind anomalies continued to evolve through ocean‐atmosphere coupling involving Bjerknes feedback and equatorial nonlinear ocean advection, until its maturity in September–November. This study clarifies the contribution of oceanic Rossby waves in the south TIO in different dynamic settings and reveals a new triggering mechanism for extreme IOD events that will help to understand IOD diversity. Plain Language Summary: The Indian Ocean Dipole (IOD) is an ocean‐atmosphere coupled climatic phenomenon which can cause severe social and economic losses in the surrounding regions such as drought in the Maritime Continent/Australia and flooding in East Africa. The IOD features a see‐saw structure accompanied by an anomalous sea surface temperature gradient, winds, and oceanic adjustments. The El Niño–Southern Oscillation in the Pacific is an important trigger to a strong IOD event. However, an extreme positive IOD event occurred in 2019 without a concurrent or ensuing El Niño. We show that the thermocline warming associated with anomalous ocean downwelling in the southwest tropical Indian Ocean triggered atmospheric convection, inducing anomalous easterly winds along the equator and hence, positive feedbacks associated with an IOD event. This study may help to understand the evolution of extreme IOD and improve IOD predictability. Key Points: The oceanic downwelling Rossby waves in the south tropical Indian Ocean is key to the 2019 extreme positive Indian Ocean Dipole (IOD)The Rossby waves induced thermocline warming, triggering wind‐evaporation‐SST feedback thus anomalous easterly winds along the equatorThe easterly wind anomalies further triggered the Bjerknes feedback and other positive feedbacks and established an extreme IOD [ABSTRACT FROM AUTHOR]

The very low‐frequency transmitter in the Northwest Cape of Australia (NWC) has previously been observed to pitch‐angle scatter electrons with energies from 30–400 keV, creating enhanced fluxes measured by low‐Earth orbiting (LEO) satellites. Here we use observations from the Energetic Particle Telescope on PROBA‐V. We compare the measured flux, as a function of local magnetic field strength, when the NWC transmitter is "on" versus "off," and find enhanced fluxes only when NWC is "on" and located on the nightside. The enhanced fluxes occur in the population gradually transitioning from "permanently trapped" to "quasi‐trapped." We show that electrons up to 800 keV, substantially higher energy than previously studied, are scattered by resonant interactions with NWC to produce enhanced fluxes. The enhanced fluxes appear at multiple L‐shells for each energy channel, consistent with resonance conditions at distinct wave normal angles, that indicate ducted interactions at L < 1.55 and unducted interactions at L > 1.65. Plain Language Summary: Radio waves with a low enough frequency can reflect off Earth's surface as well as the ionosphere, a layer of charged particles above Earth's atmosphere created by the Sun's ionization of the upper atmosphere. These waves bounce back and forth in the Earth‐ionosphere waveguide, enabling AM (Amplitude Modulation) radio to be heard at large distances, for example. Transmitters with even lower frequencies than AM radio, in the tens of kiloHertz range, are used to communicate with submarines just below the ocean's surface that can be located on the other side of the world. The ionosphere is not a perfect reflector, though, and some of the transmitter wave power escapes into Earth's magnetosphere, a region where charged particles like electrons can be trapped for many months on magnetic field lines. The radio waves can scatter the trapped electrons into Earth's atmosphere, where they rapidly lose energy and no longer pose a threat to space‐based assets. Understanding how naval transmitters scatter trapped electrons is needed to help us explain why electrons stay trapped for as long as they do, and enable us to predict radiation damage to the growing number of satellites that orbit Earth with low altitudes, which limits the satellite's useful lifetime. Key Points: The ground‐based transmitter in northwest Australia scatters electrons into the drift loss coneThe Energetic Particle Telescope on the PROBA‐V satellite sees enhanced fluxes at 500–800 keV from low‐Earth orbitThe enhanced fluxes occur at energy‐dependent L‐shells that are consistent with the resonance condition for ducted and nonducted waves [ABSTRACT FROM AUTHOR]

Using observation/reanalysis data, influences of the Interdecadal Pacific Oscillation (IPO) on the frequency of the locally amplified Ningaloo Niño (i.e., events with local air‐sea interactions playing an important role) and their mechanisms are investigated in this study. It is found that the ratio of the locally amplified Ningaloo Niño increases during the negative phase of the IPO. This is due to positive interdecadal sea surface temperature anomalies to the northwest of Australia that promote deep atmospheric convection and anomalous cyclone off the west coast of Australia through a Matsuno‐Gill response. Based on a mixed layer heat budget analysis using outputs from a regional ocean model, it is shown that an enhanced warming of anomalously thin mixed layer by the shortwave radiation contributes dominantly to the interdecadal sea surface temperature anomalies. The shallow mixed layer depth is suggested to be generated by anomalously weak winds associated with the negative IPO. Plain Language Summary: Ningaloo Niño is an anomalously warm ocean condition along the west coast of Australia and causes heat stress to marine species (e.g., coral bleaching). There are two mechanisms that give rise to the Ningaloo Niño. One is atmospheric and oceanic remote forcing, which is associated with La Niña, and the other is associated with local air‐sea interactions. A Ningaloo Niño event in which the local air‐sea interactions play an important role is called "locally amplified Ningaloo Niño." In this study, it is confirmed that the Ningaloo Niño occurs more frequently during the negative Interdecadal Pacific Oscillation (IPO) than the positive IPO. Moreover, it is revealed for the first time that the ratio of the locally amplified events increases during the negative IPO due to intensified air‐sea interaction associated with warm ocean condition to the northwest of Australia. These results and mechanisms may contribute to improve decadal prediction of the Ningaloo Niño. Key Points: Ningaloo Niño occurs more frequently during the negative phase of the Interdecadal Pacific Oscillation (IPO)The ratio of the locally amplified Ningaloo Niño increases during the negative IPOPositive interdecadal SST anomalies to the northwest of Australia during the negative IPO enhance the local air‐sea interaction [ABSTRACT FROM AUTHOR]

The steepness of the beach face is a fundamental parameter for coastal morphodynamic research. Despite its importance, it remains extremely difficult to obtain reliable estimates of the beach‐face slope over large spatial scales (thousands of km of coastline). In this letter, a novel approach to estimate this slope from time series of satellite‐derived shoreline positions is presented. This new technique uses a frequency domain analysis to find the optimum slope that minimizes high‐frequency tidal fluctuations relative to lower‐frequency erosion/accretion signals. A detailed assessment of this new approach at eight locations spanning a range of tidal regimes, wave climates, and sediment grain sizes shows strong agreement (R2 = 0.93) with field measurements. The automated technique is then applied across thousands of beaches in eastern Australia and California, USA, revealing similar regional‐scale distributions along these two contrasting coastlines and highlights the potential for new global‐scale insight to beach‐face slope spatial distribution, variability, and trends. Plain Language Summary: How steep a beach is can dictate the way the beach interacts with the incoming ocean waves and therefore is of paramount importance for coastal scientists and engineers, coastal flood modelers, and swim safety officers. However, despite its importance, it is impractical to obtain reliable estimates of the "typical" beach‐face slope along large lengths of sandy coastlines (hundreds to thousands of km) because of the logistics that would be necessary to visit many sites repeatedly to obtain these measurements. This letter describes a new technique to estimate the beach‐face slope in the absence of field observations, relying instead on long‐term publicly available satellite observations and a global tide model. This technique is then applied to thousands of beaches along the coastlines of eastern Australia and California in the United States. Key Points: A novel remote sensing technique to estimate beach‐face slopes from satellite imagery and modeled tides is presentedTime series of shoreline change are transformed into frequency domain to find the slope that minimizes high‐frequency tidal fluctuationsValidation against in situ data shows high accuracy across sites ranging in grain size, tidal range, and wave climate [ABSTRACT FROM AUTHOR]

Satellite observational data and a regional ocean model are used to understand the evolution of Ningaloo Niño (NN) anomalies near Western Australian coast. In observation and high‐resolution (~3 km) simulations, coastally trapped positive sea level anomalies (SLAs), originated largely from the Indonesian Throughflow, are transmitted westward by mesoscale eddies. Few eddies propagate long distances offshore due to dissipation, and as a result NN signatures are predominantly confined near the coast. In coarse‐resolution (~100 km) simulations that cannot resolve eddies, oceanic anomalies propagate swiftly as long Rossby waves with much weaker dissipation and more anomalies spread to the ocean interior. Eddy‐enhanced surface warming promotes surface latent heat release and mesoscale air‐sea interactions, which acts to damp NN surface warming. These processes are not resolved by coarse‐resolution models. This study highlights the importance of resolving mesoscale oceanic processes in the simulation and prediction of NN. Plain Language Summary: Ningaloo Niño (NN) is a surface warming surge phenomenon of the southeast Indian Ocean. Here we describe how NN anomalies develop in high‐ (~3 km) and low‐resolution (~100 km) ocean model simulations. We found that in high‐resolution simulations and observational data, the sea level rise and warming of the NN spread offshore as eddies with wavelengths of 10–500 km. Because eddies move slowly and are subjected to strong dissipation, NN anomalies cannot spread long distance offshore and tend to concentrate near the west coast of Australia. However, these eddies are not resolved in low‐resolution simulations. Instead, NN anomalies travel westward quickly as long free Rossby waves without obvious dissipation. Eddies also enhance local surface warming anomalies and cause strong latent heat loss, leaving impacts on the local climate. These processes are absent in low‐resolution simulations. Therefore, it seems necessary to take into account effects of oceanic mesoscale eddies (OMEs) in the simulation and prediction of NN. Key Points: Coastally trapped warming signatures near Western Australia are transmitted westward by oceanic mesoscale eddiesCoarse‐resolution models preclude eddy effects and exhibit major biases in sea level and SST anomalies of Ningaloo NiñoEddy‐induced SST anomalies cause strong latent heat release to the atmosphere, which is missing in coarse‐resolution models [ABSTRACT FROM AUTHOR]

Australia experienced its driest calendar year on record in 2019. A number of factors contributed to the persistently dry conditions, including a record‐low number of cyclones in the Australian region south of 30°S as well as very high numbers of anticyclones during the southern wet season (April–September). The record year is likely a result of natural climate variability together with an underlying trend. The number of cyclones in southern Australia has decreased since 1979, and the number of cool season anticyclones has increased, although large interannual variability means that these trends currently cannot be distinguished from natural variability. However, the longer NCEP1 and JRA55 reanalyses provide evidence of a long‐term decline in cyclone frequency in southern Australia since the 1950s. Plain Language Summary: In southern Australia, low pressure systems are very important for rainfall, and high pressure systems usually bring dry weather. During 2019, southern Australia had the fewest low pressure systems in at least 50 years and more high pressure systems than normal. This may have contributed to the very low rainfall totals experienced that year. Key Points: Southern Australia had record‐low numbers of cyclones in 2019Anticyclones were also more common than normal in southern Australia, especially between April–SeptemberThere is a long‐term increase in anticyclones and decrease in cyclones [ABSTRACT FROM AUTHOR]

Climate change projections for the Australian monsoon have been highly uncertain in previous generations of coupled climate models. The new Coupled Model Intercomparison Project Phase 6 (CMIP6) ensemble provides an opportunity to address the uncertainty in future projections for northern Australia. We find that the range in Australian monsoon projections from the available CMIP6 ensemble is substantially reduced compared to CMIP5, although models continue to disagree on the magnitude and direction of change. While previous CMIP5 studies identified warming in the western equatorial Pacific as important for Australian monsoon projections, here we show that the western Pacific is not strongly connected to northern Australian precipitation changes in the CMIP6 models. By comparing groups of models based on their future projections, we note that the model‐to‐model differences in Australian monsoon projections are congruent with the zonally averaged precipitation response in the Southern Hemisphere tropics within each model. Key Points: Australian monsoon changes are smaller in the available CMIP6 ensemble than the CMIP5 ensembleCMIP6 models still disagree on changes to Australian monsoon precipitation in a warmer worldAustralian monsoon changes are congruent with the zonal mean precipitation change, more evident in CMIP6 than CMIP5 [ABSTRACT FROM AUTHOR]

Widespread coral bleaching across the Great Barrier Reef (GBR) in 2016 is often reportedly caused by El Niño and/or global warming. However, the GBR is not in a region where it is straightforward to anticipate sea surface temperature (SST) warming during El Niño, and the role of climate change is unclear. This study uses a diverse range of observations to investigate the physical causes of SST anomalies that developed on the GBR in 2016. Warm SST anomalies developed in two stages. Initial warming was caused by El Niño shifting the global‐scale pattern of convection, increasing solar radiation in the Coral Sea. The warm anomaly was extended and amplified near the coast by a terrestrial heat wave propagating across eastern Australia, further warming the GBR through turbulent heat flux. It is concluded that El Niño caused the SST anomaly, and global warming increased its amplitude and extended it by several months. Key Points: A quantitative heat budget analysis of the 2016 marine heat wave in the Great Barrier Reef lights a path to large‐scale climate processesThe waning El Niño of 2015/2016 warmed regional seas with solar radiation; a terrestrial heat wave in Australia intensified coastal warmingLong‐term trends in marine and terrestrial records clarify role of global warming, widespread coral mortality in 2016 unlikely without it [ABSTRACT FROM AUTHOR]

An analysis of Argo data reveals that the subantarctic mode water (SAMW) in the South Indian Ocean (SIO), characterized by a vertical potential vorticity (PV) minimum, decreases by 10% in volume from 2004 to 2018. Most of this decrease occurs at the 26.8–26.9 kg m−3 density range which forms southwest of Australia, while a slight volume increase occurs at 26.6–26.8 kg m−3. Further analysis indicates that the weakening of the Mascarene High and westerly winds in the SIO reduces the evaporation‐precipitation, surface heat flux, and Ekman pumping and shoals the mixed layer southwest of Australia, which leads to a volume decrease at 26.8–26.9 kg m−3 in approximately 3 years. West of 90°E, the parameters exhibit the opposite change, leading to a volume increase at 26.6–26.8 kg m−3. This result suggests that surface winds play an important role in the variability of the SIO SAMW volume during the Argo period. Plain Language Summary: During austral winter in the subantarctic zone, a water mass called the subantarctic mode water with homogeneous properties (temperature, salinity) forms, sinks, and moves to the interior of the ocean. The formation and transport of the mode water are crucial for the climate, as the water takes up heat, freshwater, carbon, oxygen, and nutrients into the ocean interior. We find a distinct volume loss of the mode water in the South Indian Ocean from 2004 to 2018. Although this mode water forms in broad density ranges in different regions, the volume loss only occurs in the dense mode water south of Australia. Moreover, the volume of the light mode water, which forms in the center of the South Indian Ocean, slightly increases. We find that surface winds control the surface heat flux and water convergence, which determine the volume change here. These winds tend to vary oppositely in the two different mode water formation regions and make the volume vary in opposition phases. This study reveals the layer dependence of the mode water volume variation and reinforces the importance of atmospheric forcing, which would possibly help interpret the heat uptake in the Southern Ocean. Key Points: Argo data reveal a subantarctic mode water volume loss in the South Indian Ocean over the period 2004–2018Most of the volume loss occurs in the density range of 26.8–26.9 kg m−3, while a volume increase occurs at 26.6–26.8 kg m−3Changes in the SAMW volume are controlled by surface forcing, which is closely related to the Mascarene High variation [ABSTRACT FROM AUTHOR]

A positive Indian Ocean Dipole (IOD) in 2019 that reached the level of the strongest events occurred in 1994 and 1997 and caused disasters in countries around the Indian Ocean. Using a quasi real‐time ensemble seasonal prediction system based on the Scale Interaction Experiment‐Frontier climate model, its occurrence was predicted a few seasons ahead and the possible impacts were warned by overcoming the so‐called winter predictability barrier. The successful prediction of such a super event at long lead time may contribute to reducing the risks of socioeconomic losses by introducing suitable measures for adaptation. Here, we have investigated possible sources of the successful prediction by analyzing covariability of intermember anomalies defined as deviations from the mean in the ensemble reforecasts. Interestingly, it is found that the potential predictability of the 2019 super positive event is linked with the preexisting El Niño Modoki in the tropical Pacific. Plain Language Summary: The Indian Ocean Dipole (IOD) is an intrinsic air‐sea coupled climate phenomenon in the tropical Indian Ocean, of which name was introduced because of the dipolar structure of both oceanic and atmospheric anomalies along the equator. Just 20 years after the introduction of IOD, another such extreme IOD event happened to emerge in 2019 and reached a level which is similar to the precedent events such as 1994 and 1997 and caused disasters in countries around the Indian Ocean. For example, many parts of Australia were seriously affected by a series of massive bushfires owing to the drier than normal conditions, while crop yield in East Africa was threatened by a plague of locusts owing to the wetter condition there. Its occurrence was predicted a few seasons ahead by overcoming the so‐called winter predictability barrier by a numerical prediction system. The successful prediction of such a super event at long lead time may contribute to reducing the risks of socioeconomic losses by introducing suitable measures for adaptation. Key Points: A positive Indian Ocean Dipole in 2019 that reached the level of the strongest events occurred in 1994 and 1997Its occurrence was predicted a few seasons ahead by overcoming the so‐called winter predictability barrierIts potential predictability is linked with the preexisting El Niño Modoki in the tropical Pacific [ABSTRACT FROM AUTHOR]

A new 3‐D seismic P wave velocity model of the Sunda‐Banda Arc Transition from local earthquake tomography reveals (i) northward subduction of oceanic lithosphere, associated with the convergence of Australia and Sundaland, as a high‐velocity zone extending down to ~200 km depth; (ii) two distinct low‐velocity zones, one immediately above the slab, which is likely a zone of partial melt, and one in the 0–40 km depth range, which is probably a magma chamber associated with active volcanoes above; and (iii) a northerly dipping high‐velocity zone that bisects the two low‐velocity anomalies, which we interpret as an underthrust forearc sliver of continental origin. Based on He3/He4 measurements from volcanic outflows, it is possible that the magma supply is contaminated by interaction with this forearc sliver as it ascends from the melt region below. Plain Language Summary: The subduction of one tectonic plate beneath another is a fundamental Earth process that is integral to the growth of continents and accommodates the emergence of new crust beneath the oceans. In general, it is the denser oceanic plates which sink into the mantle, while the more buoyant continental plates remain at the surface. In this study, we investigate the Sunda‐Banda region in southeast Indonesia, where convergence of the Eurasian and Australian plates has resulted in the collision of a volcanic arc and the Australian continent. By exploiting earthquake signals recorded by a set of stations at the surface, we show that a sliver of continental forearc (region between the subduction trench and volcanic arc) has been thrust beneath the overriding plate due to the northward motion of Australia and now sits above the downgoing oceanic plate. Our new results also suggest that the underthrust forearc material may contribute to the contamination of volcanic products by crustal material of continental origin. Key Points: Local earthquake P wave tomography is applied to a new arrival time data set from the Sunda‐Banda Arc Transition in IndonesiaA forearc sliver of continental origin is underthrusted beneath Flores, above a subducting oceanic slabPartial melting triggered by the subducting oceanic slab is contaminated by the forearc sliver and upper plate on its way to the surface [ABSTRACT FROM AUTHOR]

Several regions of the world, including the east coast of Australia, are characterized by the occurrence of low‐pressure systems with a range of different dynamical structures, including tropical, extratropical, and hybrid cyclones. Future changes in the occurrence of cyclones are better understood if storms are classified according to their dynamical structure. Therefore, we apply a classification of cyclones according to their cold‐core or warm‐core structure to an ensemble of regional climate model simulations. First, we show that historical simulations reproduce well the reanalysis results in terms of cyclone classification. We then show that once cyclone classification is applied, projections of future cyclone activity become more robust, including a decrease in the occurrence of both cold‐core and warm‐core cyclones. Finally, we show that in a warmer climate warm‐core hybrid cyclone activity could increase close to the coast, while the associated rainfall and wind are projected to increase. Plain Language Summary: Cyclones in the tropics derive their energy from the temperature difference between warm ocean waters and the atmosphere and their interior is warmer than the environment (warm core), while cyclones in the midlatitudes derive their energy from differences in the atmospheric temperature and density at different locations and their interior is colder than the environment (cold core). In subtropical regions both types of cyclone can form. Also in those regions cyclones known as hybrid cyclones form, with mixed tropical‐extratropical features, such as a partial lower tropospheric warm core and a partial upper tropospheric cold core. This study is focused on cyclones along the eastern coast of Australia. Here we show that dividing cyclones in different classes according to their thermal structure provides a better framework to interpret changes in cyclone activity at subtropical latitudes. This study has two main results. First, classifying cyclones adds value to climate projection robustness. A large number of models agree on the decrease in the occurrence of both cold‐core and warm‐core cyclones. The study also indicates increased occurrence of hybrid cyclones close to the Australian coast. Second, the study shows evidence of future changes in cyclone‐related impacts, such as an increase in the associated rainfall. Key Points: A physically based classification of hybrid cyclones is applied to an ensemble of regional climate model simulationsThe cyclone classification method adds value to the projections of future cyclone activity, making them more robustResults indicate future changes (2060–2079) toward more intense impacts associated with hybrid cyclones [ABSTRACT FROM AUTHOR]

Satellite solar‐induced chlorophyll fluorescence (SIF) products from the Global Ozone Monitoring Experiment 2 (GOME‐2) and Orbiting Carbon Observatory 2 (OCO‐2) are used to investigate the responses of vegetation growth to the 2019 heat wave in Australia. Both satellite SIF data sets are more sensitive to water and heat stress than is the greenness‐based vegetation index (enhanced vegetation index). Moreover, the OCO‐2 SIF observations show a more significant reduction and earlier response to the heat stress than does GOME‐2 SIF, indicating that the two satellite SIF data sets differ in how they monitor the drought and heat wave event due to the different timing of observations. Eddy covariance measurements confirm the different responses of dryland vegetation to the 2019 heat wave at a subdaily time scale. The differences in the timing of the satellite SIF products can be used to assess different elements of the impact of heat and water stress on Australian dryland ecosystems. Plain Language Summary: An extreme heat wave occurred across Australia during the summer of 2019, and the high air temperatures and low precipitation affected the vegetation. We used two satellite solar‐induced chlorophyll fluorescence (SIF) data sets to investigate the response of vegetation growth to the extremely high temperatures in Australia. Vegetation growth was reduced during the 2019 summer, but SIF measurements allowed us to separate the impact of the heat wave on the vegetation in the morning and in the afternoon. Our work illustrates how the timing of satellite observations provides different information on how dryland vegetation responds to heat waves in Australia. Key Points: The impact of the 2019 heat wave on Australian dryland ecosystems is examinedSolar‐induced fluorescence (SIF) shows stronger reductions to heat and water stress than does vegetation indexSIF observed at noon responds to the heat stress earlier than does that measured in the morning in Australia [ABSTRACT FROM AUTHOR]

Despite decades of study, the mechanisms that lead to the localization of intracontinental seismicity remain vigorously debated. We find a very strong correlation between the attenuation of teleseismic P waves and the occurrence of intraplate seismicity in Australia. The regions with the highest attenuation host ~2 orders of magnitude more earthquakes per unit of area than the least attenuating regions. We argue that the attenuation we observe is produced by lateral variations in the thickness and/or viscosity of the lithospheric mantle and further suggest that the correlation we document implies that lithospheric mantle structure exerts first‐order controls on the localization of intraplate seismicity. Key Points: Australian seismicity is highly correlated with seismic attenuationAttenuation is a likely proxy for the viscous strength of the lithosphereWeaker lithosphere leads to faster loading of crustal faults [ABSTRACT FROM AUTHOR]

High‐resolution optical satellite imagery is used to quantify vertical surface deformation associated with the intraplate 20 May 2016 Mw 6.0 Petermann Ranges earthquake, Northern Territory, Australia. The 21 ± 1‐km‐long NW trending rupture resulted from reverse motion on a northeast dipping fault. Vertical surface offsets of up to 0.7 ± 0.1m distributed across a 0.5‐to‐1‐km‐wide deformation zone are measured using the Iterative Closest Point algorithm to compare preearthquake and postearthquake digital elevation models derived from WorldView imagery. The results are validated by comparison with field‐based observations and interferometric synthetic aperture radar. The pattern of surface uplift is consistent with distributed shear above the propagating tip of a reverse fault, leading to both an emergent fault and folding proximal to the rupture. This study demonstrates the potential for quantifying modest (<1 m) vertical deformation on a reverse fault using optical satellite imagery. Key Points: The 20 May 2016 Mw 6.0 Petermann Ranges earthquake, Australia resulted from reverse faultingIterative Closest Point (ICP) comparison of preearthquake and postearthquake DEMs derived from optical satellite imageryA 21‐km‐long rupture with maximum vertical deformation of 0.7 m and broad 0.5‐ to 1‐km‐wide deformation zone [ABSTRACT FROM AUTHOR]

Many general circulation models fail to capture the observed frequency of atmospheric blocking events in the Northern Hemisphere; however, few studies have examined models in the Southern Hemisphere and those studies that have, have often been based on only a few models. To provide a comprehensive view of how the current generation of coupled general circulation models performs in the Southern Hemisphere and how blocking frequency changes under enhanced greenhouse gas forcing, we examine the output of 23 models from the Coupled Model Intercomparison Project Phase 5 (CMIP5). We find that models have differing biases during winter, when blocking occurrence is highest, though models underestimate blocking frequency south of Australia during summer. We show that models generally have a reduction in blocking frequency with future anthropogenic forcing, particularly in the Australia‐New Zealand sector with the number of winter blocked days reduced by about one third by the end of the 21st century. Plain Language Summary: Atmospheric blocking is a process in which an atmospheric wave breaks, diverting the jet stream and any incoming storms to the north or south. A blocking event is characterized by high pressure on the poleward side and low pressure on the equatorward side and persists for upward of 4 days. A key feature of blocks is their persistence, which can lead to events, which have significant impacts on society including heat waves in summer and periods of extreme cold in winter. Climate models often do not simulate enough blocking events, though most research on this problem has focused on the Northern Hemisphere and less is known about the Southern Hemisphere. We survey 23 climate models and show that during winter some models simulate too many blocking events, while others simulate too few, whereas during summer, almost all models simulate too few events to the south of Australia. We also show that with higher concentrations of greenhouse gases we expect there to be less blocking, particularly to the south of Australia and over New Zealand during winter. Key Points: We provide a comprehensive survey of Southern Hemisphere blocking using a large number of coupled modelsFuture projections generally suggest an overall decrease in Southern Hemisphere blocking frequencyThere is strong model agreement on blocking frequency decreases to the south of Australia during austral winter [ABSTRACT FROM AUTHOR]

During the summer months, there is a semipermanent trough in the low‐level easterlies over the west coast of Australia. This "West Coast Trough" plays an important role in summer severe weather in western Australia including thunderstorms and severe heat waves. The land‐sea contrast is believed to be the driver of the location of this trough. As land masses are warming more quickly than their surrounding oceans, it is timely to readdress the drivers of the location and intensity of this important climatological feature. Using a 20‐year regional climate modeling simulation, we show that Australian orography is critical to the accurate representation of the trough in climate models, in contrast to earlier low‐resolution studies. Plain language summary: During the summer, the average weather pattern in Western Australia includes a trough near the west coast. For this trough to exist in climate models, they need to include Australian elevation including the plateau in Western Australia. Otherwise, the trough does not exist and summer rainfall is lower. Key Points: Model orography is critical for accurate representation of the Australian West Coast TroughIn simulations without topography, summer rainfall and midtroposphere temperature are reduced over Western Australia [ABSTRACT FROM AUTHOR]