ORCID Profile
0000-0001-6020-1603
Current Organisation
University of New South Wales
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Research Topics
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Top 5 Research Topics
ANZSRC Field of Research (FoR)
Atmospheric Sciences | Atmospheric Dynamics | Physical Oceanography | Climatology (Incl. Palaeoclimatology) | Climate Change Processes | Physical Oceanography | Surfacewater Hydrology | Quaternary Environments | Physical Geography and Environmental Geoscience | Oceanography | Atmospheric sciences | Geomorphology and Regolith and Landscape Evolution | Meteorology | Climatology (excl. Climate Change Processes) | Physical oceanography | Meteorology | Climate change processes | Atmospheric dynamics |
ANZSRC Socio-Economic Objective (SEO)
Effects of Climate Change and Variability on Australia (excl. Social Impacts) | Atmospheric Processes and Dynamics | Climate Variability (excl. Social Impacts) | Climate Change Models | Climate variability | Climate change | Weather | Global Effects of Climate Change and Variability (excl. Australia, New Zealand, Antarctica and the South Pacific) (excl. Social Impacts) | Expanding Knowledge in the Earth Sciences
Related Links
Publications
Intercomparison of Heat Fluxes in the South Atlantic. Part I: The Seasonal Cycle
Publisher: American Meteorological Society
Date: 02-2003
Uncertainty in near-term global surface warming linked to tropical Pacific climate variability
Publisher: Springer Science and Business Media LLC
Date: 30-04-2019
DOI: 10.1038/S41467-019-09761-2
Abstract: Climate models generally simulate a long-term slowdown of the Pacific Walker Circulation in a warming world. However, despite increasing greenhouse forcing, there was an unprecedented intensification of the Pacific Trade Winds during 1992–2011, that co-occurred with a temporary slowdown in global surface warming. Using ensemble simulations from three different climate models starting from different initial conditions, we find a large spread in projected 20-year globally averaged surface air temperature trends that can be linked to differences in Pacific climate variability. This implies diminished predictive skill for global surface air temperature trends over decadal timescales, to a large extent due to intrinsic Pacific Ocean variability. We show, however, that this uncertainty can be considerably reduced when the initial oceanic state is known and well represented in the model. In this case, the spatial patterns of 20-year surface air temperature trends depend largely on the initial state of the Pacific Ocean.
Dynamics and Predictability of El Niño–Southern Oscillation: An Australian Perspective on Progress and Challenges
Publisher: American Meteorological Society
Date: 03-2019
Abstract: El Niño and La Niña, the warm and cold phases of El Niño–Southern Oscillation (ENSO), cause significant year-to-year disruptions in global climate, including in the atmosphere, oceans, and cryosphere. Australia is one of the countries where its climate, including droughts and flooding rains, is highly sensitive to the temporal and spatial variations of ENSO. The dramatic impacts of ENSO on the environment, society, health, and economies worldwide make the application of reliable ENSO predictions a powerful way to manage risks and resources. An improved understanding of ENSO dynamics in a changing climate has the potential to lead to more accurate and reliable ENSO predictions by facilitating improved forecast systems. This motivated an Australian national workshop on ENSO dynamics and prediction that was held in Sydney, Australia, in November 2017. This workshop followed the aftermath of the 2015/16 extreme El Niño, which exhibited different characteristics to previous extreme El Niños and whose early evolution since 2014 was challenging to predict. This essay summarizes the collective workshop perspective on recent progress and challenges in understanding ENSO dynamics and predictability and improving forecast systems. While this essay discusses key issues from an Australian perspective, many of the same issues are important for other ENSO-affected countries and for the international ENSO research community.
Simulated response of South Atlantic Subtropical Mode Water to air-sea processes
Publisher: Wiley
Date: 11-03-2021
Common cause for severe droughts in South America and marine heatwaves in the South Atlantic
Publisher: Springer Science and Business Media LLC
Date: 08-07-2019
An Automated Climatology of Cool-Season Cutoff Lows over Southeastern Australia and Relationships with the Remote Climate Drivers
Publisher: American Meteorological Society
Date: 12-2021
Abstract: Cutoff low pressure systems have been found to be the synoptic system responsible for the majority of rainfall in southeastern Australia during the cool season (April–October inclusive). Meanwhile, rainfall in southeastern Australia at the seasonal and interannual scale is known to be related to remote climate drivers, such as El Niño–Southern Oscillation, the Indian Ocean dipole, and the southern annular mode. In this study, a new automated tracking scheme to identify synoptic scale cutoff lows is developed, and then applied to 500-hPa geopotential height data from the NCEP1 and ERA-Interim reanalyses, to create two databases of cool-season cutoff lows for southeastern Australia for the years 1979–2018 inclusive. Climatological characteristics of cutoff lows identified in both reanalyses are presented and compared, highlighting differences between the NCEP1 and ERA-Interim reanalyses over the Australian region. Finally, cool-season and monthly characteristics of cutoff low frequency, duration, and location are plotted against cool-season and monthly values of climate driver indices (oceanic Niño, dipole mode, and Antarctic Oscillation indices), to identify any evidence of linear correlation. Correlations between these aspects of cutoff low occurrence and the remote drivers were found to be statistically significant at the 95% level for only a single isolated month at a time, in contrast to results predicted by previous works. It is concluded that future studies of cutoff low variability over SEA should employ identification criteria that capture systems of only upper-level origin, and differentiate between cold-cored and cold-trough systems.
Drier tropical and subtropical Southern Hemisphere in the mid-Pliocene Warm Period
Publisher: Springer Science and Business Media LLC
Date: 10-08-2002
DOI: 10.1038/S41598-020-68884-5
Abstract: Thermodynamic arguments imply that global mean rainfall increases in a warmer atmosphere however, dynamical effects may result in more significant ersity of regional precipitation change. Here we investigate rainfall changes in the mid-Pliocene Warm Period (~ 3 Ma), a time when temperatures were 2–3ºC warmer than the pre-industrial era, using output from the Pliocene Model Intercomparison Projects phases 1 and 2 and sensitivity climate model experiments. In the Mid-Pliocene simulations, the higher rates of warming in the northern hemisphere create an interhemispheric temperature gradient that enhances the southward cross-equatorial energy flux by up to 48%. This intensified energy flux reorganizes the atmospheric circulation leading to a northward shift of the Inter-Tropical Convergence Zone and a weakened and poleward displaced Southern Hemisphere Subtropical Convergences Zones. These changes result in drier-than-normal Southern Hemisphere tropics and subtropics. The evaluation of the mid-Pliocene adds a constraint to possible future warmer scenarios associated with differing rates of warming between hemispheres.
How did ocean warming affect Australian rainfall extremes during the 2010/2011 La Niña event?
Publisher: American Geophysical Union (AGU)
Date: 19-11-2015
DOI: 10.1002/2015GL065948
ENSO Atmospheric Teleconnections
Publisher: Wiley
Date: 23-10-2020
CMIP5 Intermodel Relationships in the Baseline Southern Ocean Climate System and With Future Projections
Publisher: American Geophysical Union (AGU)
Date: 06-2021
DOI: 10.1029/2020EF001873
Abstract: Climate models exhibit a broad range in the simulated properties of the climate system. In the early historical period, the absolute global mean surface air temperature in Coupled Model Intercomparison Project, Phase 5 (CMIP5) models spans a range of ∼12°C – 15°C. Other climate variables may be linked to global mean temperature, and so accurate representation of the baseline climate state is crucial for meaningful future climate projections. In CMIP5 baseline climate states, statistically significant intermodel correlations between Southern Ocean surface temperature, outgoing shortwave radiation, cloudiness, the position of the mid‐latitude eddy‐driven jet, and Antarctic sea ice area are found. The baseline temperature relationships extend to projected future changes in the same set of variables, impacting on the projected global mean surface temperature change. Models with initially cooler Southern Ocean tend to exhibit more global warming, and vice versa for initially warmer models. These relationships arise due to a “capacity for change”. For ex le, cold‐biased models tend to have more cloud cover, sea ice, and equatorward jet initially, and thus a greater capacity to lose cloud cover and sea ice, and for the jet to shift poleward under global warming. A first look at emerging data from CMIP6 reveals a shift of the relationship from the Southern Ocean towards the Antarctic region, possibly due to reductions in Southern Ocean biases, such as in westerly wind representation.
Mid-Pliocene El Niño/Southern Oscillation suppressed by Pacific intertropical convergence zone shift
Publisher: Springer Science and Business Media LLC
Date: 11-08-2022
Can Australian Multiyear Droughts and Wet Spells Be Generated in the Absence of Oceanic Variability?
Publisher: American Meteorological Society
Date: 19-08-2016
Abstract: Anomalous conditions in the tropical oceans, such as those related to El Niño–Southern Oscillation and the Indian Ocean dipole, have been previously blamed for extended droughts and wet periods in Australia. Yet the extent to which Australian wet and dry spells can be driven by internal atmospheric variability remains unclear. Natural variability experiments are examined to determine whether prolonged extreme wet and dry periods can arise from internal atmospheric and land variability alone. Results reveal that this is indeed the case however, these dry and wet events are found to be less severe than in simulations incorporating coupled oceanic variability. Overall, ocean feedback processes increase the magnitude of Australian rainfall variability by about 30% and give rise to more spatially coherent rainfall impacts. Over mainland Australia, ocean interactions lead to more frequent extreme events, particularly during the rainy season. Over Tasmania, in contrast, ocean–atmosphere coupling increases mean rainfall throughout the year. While ocean variability makes Australian rainfall anomalies more severe, droughts and wet spells of duration longer than three years are equally likely to occur in both atmospheric- and ocean-driven simulations. Moreover, they are essentially indistinguishable from what one expects from a Gaussian white noise distribution. Internal atmosphere–land-driven megadroughts and megapluvials that last as long as ocean-driven events are also identified in the simulations. This suggests that oceanic variability may be less important than previously assumed for the long-term persistence of Australian rainfall anomalies. This poses a challenge to accurate prediction of long-term dry and wet spells for Australia.
An analysis of late twentieth century trends in Australian rainfall
Publisher: Wiley
Date: 21-07-2008
DOI: 10.1002/JOC.1736
Projected Changes to the Southern Hemisphere Ocean and Sea Ice in the IPCC AR4 Climate Models
Publisher: American Meteorological Society
Date: 06-2009
Abstract: Fidelity and projected changes in the climate models, used for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4), are assessed with regard to the Southern Hemisphere extratropical ocean and sea ice systems. While in idual models span different physical parameterizations and resolutions, a major component of intermodel variability results from surface wind differences. Projected changes to the surface wind field are also central in modifying future extratropical circulation and internal properties. A robust southward shift of the circumpolar current and subtropical gyres is projected, with a strong spinup of the Atlantic gyre. An associated increase in the core strength of the circumpolar circulation is evident however, this does not translate into robust increases in Drake Passage transport. While an overarching oceanic warming is projected, the circulation-driven poleward shift of the temperature field explains much of the midlatitude warming pattern. The effect of this shift is less clear for salinity, where, instead, surface freshwater forcing dominates. Surface warming and high-latitude freshwater increases drive intensified stratification, and a shoaling and southward shift of the deep mixed layers. Despite large intermodel differences, there is also a robust weakening in bottom water formation and its northward outflow. At the same time the wind intensification invigorates the upwelling of deep water, transporting warm, salty water southward and upward, with major implications for sequestration and outgassing of CO2. A robust decrease is projected for both the sea ice concentration and the seasonal cycling of ice volume, potentially altering the salt and heat budget at high latitudes.
Changing El Niño–Southern Oscillation in a warming climate
Publisher: Springer Science and Business Media LLC
Date: 17-08-2021
Global and Regional Climate Response to Late Twentieth-Century Warming over the Indian Ocean
Publisher: American Meteorological Society
Date: 04-2010
Abstract: The global and regional climate response to a warming of the Indian Ocean is examined in an ensemble of atmospheric general circulation model experiments. The most marked changes occur over the Indian Ocean, where the increase in tropical SST is found to drive enhanced convection throughout the troposphere. In the extratropics, the warming Indian Ocean is found to induce a significant trend toward the positive phase of the northern annular mode and also to enhance the Southern Hemisphere storm track over Indian Ocean longitudes as a result of stronger meridional temperature gradients. Convective outflow in the upper levels over the warming Indian Ocean leads to a trend in subsidence over the Indian and Asian monsoon regions extending southeastward to Indonesia, the eastern Pacific, and northern Australia. Regional changes in Australia reveal that this anomalous zone of subsidence induces a drying trend in the northern regions of the continent. The long-term rainfall trend is exacerbated over northeastern Australia by the anomalous anticyclonic circulation, which leads to an offshore trend in near-surface winds. The confluence of these two factors leads to a drying signal over northeastern Australia, which is detectable during austral autumn. The rapid, late twentieth-century warming of the Indian Ocean may have contributed to a component of the observed drying trend over northeastern Australia in this season via modifications to the vertical structure of the tropical wind field.
The Indo-Australian monsoon and its relationship to ENSO and IOD in reanalysis data and the CMIP3/CMIP5 simulations
Publisher: Springer Science and Business Media LLC
Date: 05-02-2013
Non-linearity in the pathway of El Niño-Southern Oscillation to the tropical North Atlantic
Publisher: American Meteorological Society
Date: 02-06-2021
Abstract: El Niño-Southern Oscillation can influence the Tropical North Atlantic (TNA), leading to anomalous sea surface temperatures (SST) at a lag of several months. Several mechanisms have been proposed to explain this teleconnection. These mechanisms include both tropical and extratropical pathways, contributing to anomalous trade winds and static stability over the TNA region. The TNA SST response to ENSO has been suggested to be nonlinear. Yet the overall linearity of the ENSO-TNA teleconnection via the two pathways remains unclear. Here we use reanalysis data to confirm that the SST anomaly (SSTA) in the TNA is nonlinear with respect to the strength of the SST forcing in the tropical Pacific, as further increases in El Niño magnitudes cease to create further increases of the TNA SSTA. We further show that the tropical pathway is more linear than the extratropical pathway by sub- iding the inter-basin connection into extratropical and tropical pathways. This is confirmed by a climate model participating in the CMIP5. The extratropical pathway is modulated by the North Atlantic Oscillation (NAO) and the location of the SSTA in the Pacific, but this modulation insufficiently explains the nonlinearity in TNA SSTA. As neither extratropical nor tropical pathways can explain the nonlinearity, this suggests that external factors are at play. Further analysis shows that the TNA SSTA is highly influenced by the preconditioning of the tropical Atlantic SST. This preconditioning is found to be associated with the NAO through SST-tripole patterns.
Modulation of Australian Precipitation by Meridional Gradients in East Indian Ocean Sea Surface Temperature
Publisher: American Meteorological Society
Date: 11-2009
Abstract: This study explores the impact of meridional sea surface temperature (SST) gradients across the eastern Indian Ocean on interannual variations in Australian precipitation. Atmospheric general circulation model (AGCM) experiments are conducted in which the sign and magnitude of eastern Indian Ocean SST gradients are perturbed. This results in significant rainfall changes for western and southeastern Australia. A reduction (increase) in the meridional SST gradient drives a corresponding response in the atmospheric thickness gradients and results in anomalous dry (wet) conditions over Australia. During simulated wet years, this seems to be due to westerly anomalies in the thermal wind over Australia and anomalous onshore moisture advection, with a suggestion that the opposite occurs during dry conditions. Thus, an asymmetry is seen in the magnitude of the forced circulation and precipitation response between the dry and wet simulations. To assess the relative contribution of the SST anomalies making up the meridional gradient, the SST pattern is decomposed into its constituent “poles,” that is, the eastern tropical pole off the northwest shelf of Australia versus the southern pole in the central subtropical Indian Ocean. Overall, the simulated Australian rainfall response is linear with regard to the sign and magnitude of the eastern Indian Ocean SST gradient. The tropical eastern pole has a larger impact on the atmospheric circulation and Australian precipitation changes relative to the southern subtropical pole. However, there is clear evidence of the importance of the southern pole in enhancing the Australian rainfall response, when occurring in conjunction with but of opposite sign to the eastern tropical pole. The observed relationship between the meridional SST gradient in the eastern Indian Ocean and rainfall over western and southeastern Australia is also analyzed for the period 1970–2005. The observed relationship is found to be consistent with the AGCM results.
A Framework to Determine the Limits of Achievable Skill for Interannual to Decadal Climate Predictions
Publisher: American Geophysical Union (AGU)
Date: 15-03-2019
DOI: 10.1029/2018JD029541
Reduced moisture sources contributed to the 2017-2019 southeast Australian drought
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-4681
Abstract: The Murray Darling Basin, located in southeast Australia, is an agriculturally rich area, providing one-third of the country& #8217 food supply. In 2017-2019 the region experienced one of its worst droughts since 1900. Rainfall in the Murray Darling Basin was consistently below average for three consecutive cool seasons, an unprecedented event on record. The drought set the extreme conditions that led later to the 2019-2020 Black Summer Bushfires. Previous studies suggest that the strong 2019 positive Indian Ocean Dipole intensified the conditions of the drought, however the state of the climate drivers cannot fully explain the onset and development of the Murray Darling Basin drought. In this study, we investigate processes other than remote climate drivers that may have triggered the drought. Using a Lagrangian model to backtrack moisture sources to southeast Australia, we show that local processes were crucial in explaining the onset and development of the drought. We identify the sources of moisture to the cool season precipitation over the Murray Darling Basin and show for the first time that the moisture supply from the Tasman Sea declined in 2017 and 2018. We further show that the expected moisture was instead transported northward by an anomalous anticyclonic circulation. Our results provide an explanation for the moisture and rainfall deficit that caused the 2017-19 drought. Understanding the processes that led to the 2017-2019 Murray Darling Basin drought is important for predicting and planning future multi-year droughts in Australia.
How sensitive are the Pacific–tropical North Atlantic teleconnections to the position and intensity of El Niño-related warming?
Publisher: Springer Science and Business Media LLC
Date: 04-06-2016
Climate impacts of the El Niño–Southern Oscillation on South America
Publisher: Springer Science and Business Media LLC
Date: 10-04-2020
South American rainfall impacts associated with inter‐El Niño variations
Publisher: American Geophysical Union (AGU)
Date: 10-2009
DOI: 10.1029/2009GL040164
Assessing the role of the ocean–atmosphere coupling frequency in the western Maritime Continent rainfall
Publisher: Springer Science and Business Media LLC
Date: 29-04-2020
A Numerical Study of the Impact of Greenhouse Gases on the South Atlantic Ocean Climatology
Publisher: Springer Science and Business Media LLC
Date: 09-2004
Drivers and impacts of the most extreme marine heatwave events
Publisher: Springer Science and Business Media LLC
Date: 09-11-2020
DOI: 10.1038/S41598-020-75445-3
Abstract: Prolonged high-temperature extreme events in the ocean, marine heatwaves, can have severe and long-lasting impacts on marine ecosystems, fisheries and associated services. This study applies a marine heatwave framework to analyse a global sea surface temperature product and identify the most extreme events, based on their intensity, duration and spatial extent. Many of these events have yet to be described in terms of their physical attributes, generation mechanisms, or ecological impacts. Our synthesis identifies commonalities between marine heatwave characteristics and seasonality, links to the El Niño-Southern Oscillation, triggering processes and impacts on ocean productivity. The most intense events preferentially occur in summer, when climatological oceanic mixed layers are shallow and winds are weak, but at a time preceding climatological maximum sea surface temperatures. Most subtropical extreme marine heatwaves were triggered by persistent atmospheric high-pressure systems and anomalously weak wind speeds, associated with increased insolation, and reduced ocean heat losses. Furthermore, the most extreme events tended to coincide with reduced chlorophyll- a concentration at low and mid-latitudes. Understanding the importance of the oceanic background state, local and remote drivers and the ocean productivity response from past events are critical steps toward improving predictions of future marine heatwaves and their impacts.
Interannual variability associated with Semiannual Oscillation in southern high latitudes
Publisher: American Geophysical Union (AGU)
Date: 20-01-2007
DOI: 10.1029/2006JD007648
Revisiting ENSO Atmospheric Teleconnections and Challenges
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-16656
Abstract: & & The warming of the equatorial Pacific associated with the El Ni& #241 o& #8211 Southern Oscillation (ENSO) causes profound impacts on rainfall and temperature in the tropics and extratropics. El Ni& #241 o drives changes in the Walker and Hadley circulations, warms the tropics and affects the neighboring ocean basins, favoring a short-term rise in global temperatures. We will present an overview of the atmospheric teleconnections driven by ENSO and its ersity focusing on the impacts over land and remote ocean basins. During El Ni& #241 o, dry conditions are generally observed in the Maritime Continent, northern South America, South Asia and South Africa, while wet weather typically occurs in southwestern North America, western Antarctica, and east Africa. Global effects during La Ni& #241 a are overall the opposite to El Ni& #241 o, however this assumption is not true for all regions. ENSO atmospheric teleconnections are non-linear in part due to different locations of the anomalous equatorial warming (Eastern versus Central Pacific events) superimposed on the Pacific mean state, as well as interactions with the annual cycle, off-equatorial regions, remote ocean basins, and other modes of climate variability. Adding to this complex behavior, ENSO teleconnections are non-stationary either due to deterministic low-frequency modulations or stochastic variability, the latter being a factor generally overlooked in the literature.& As the world warms in response to greenhouse gas forcing, ENSO atmospheric teleconnections are expected to change, despite large uncertainties in ENSO projections. We will discuss the limitations of climate models in representing realistic teleconnections from the tropical Pacific to remote regions and some of the challenges for future projections.& &
Linking ENSO to Synoptic Weather Systems in Eastern Australia
Publisher: American Geophysical Union (AGU)
Date: 08-08-2023
DOI: 10.1029/2023GL104814
Abstract: El Niño‐Southern Oscillation (ENSO) is the main driver of interannual east Australian rainfall variability, but its link with rain‐producing synoptic weather systems is unclear. By tracking low pressure systems in ERA5 over 1979 to 2021, we find that springtime cyclones are linked to variations in the large‐scale atmospheric circulation during ENSO events. On spring days with a cyclone during La Niña, a pressure dipole occurs with a strong anticyclonic anomaly southeast of Australia and a cyclonic anomaly over eastern Australia. The northeasterly circulation directs tropical moisture toward eastern Australia, and coupled with induced ascent, promotes rainfall in this region. Both dynamical and thermodynamical changes are important for the rainfall response. An almost opposite circulation response occurs on cyclone days during El Niño events: high‐pressure over the Australian continent reduces rainfall in eastern Australia. These synoptic setups resemble the seasonal‐mean Rossby wave teleconnections, indicating a link between weather systems and ENSO.
Editorial: Dynamics and impacts of tropical climate variability: Understanding trends and future projections
Publisher: Frontiers Media SA
Date: 07-02-2023
Estimating ensemble size requirements of AGCM simulations
Publisher: Springer Science and Business Media LLC
Date: 08-2008
Cold Tongue and Warm Pool ENSO Events in CMIP5: Mean State and Future Projections
Publisher: American Meteorological Society
Date: 10-04-2014
DOI: 10.1175/JCLI-D-13-00437.1
Abstract: The representation of the El Niño–Southern Oscillation (ENSO) under historical forcing and future projections is analyzed in 34 models from the Coupled Model Intercomparison Project phase 5 (CMIP5). Most models realistically simulate the observed intensity and location of maximum sea surface temperature (SST) anomalies during ENSO events. However, there exist systematic biases in the westward extent of ENSO-related SST anomalies, driven by unrealistic westward displacement and enhancement of the equatorial wind stress in the western Pacific. Almost all CMIP5 models capture the observed asymmetry in magnitude between the warm and cold events (i.e., El Niños are stronger than La Niñas) and between the two types of El Niños: that is, cold tongue (CT) El Niños are stronger than warm pool (WP) El Niños. However, most models fail to reproduce the asymmetry between the two types of La Niñas, with CT stronger than WP events, which is opposite to observations. Most models capture the observed peak in ENSO litude around December however, the seasonal evolution of ENSO has a large range of behavior across the models. The CMIP5 models generally reproduce the duration of CT El Niños but have biases in the evolution of the other types of events. The evolution of WP El Niños suggests that the decay of this event occurs through heat content discharge in the models rather than the advection of SST via anomalous zonal currents, as seems to occur in observations. No consistent changes are seen across the models in the location and magnitude of maximum SST anomalies, frequency, or temporal evolution of these events in a warmer world.
Representative Transmission Coefficient for Evaluating the Wave Attenuation Performance of 3D Floating Breakwaters in Regular and Irregular Waves
Publisher: MDPI AG
Date: 06-04-2021
DOI: 10.3390/JMSE9040388
Abstract: Wave attenuation performance is the prime consideration when designing any floating breakwater. For a 2D hydrodynamic analysis of a floating breakwater, the wave attenuation performance is evaluated by the transmission coefficient, which is defined as the ratio between the transmitted wave height and the incident wave height. For a 3D breakwater, some researchers still adopted this evaluation approach with the transmitted wave height taken at a surface point, while others used the mean transmission coefficient within a surface area. This paper aims to first examine the rationality of these two evaluation approaches via verified numerical simulations of 3D heave-only floating breakwaters in regular and irregular waves. A new index—a representative transmission coefficient—is then presented for one to easily compare the wave attenuation performances of different 3D floating breakwater designs.
Climate and agricultural risk: Assessing the impacts of major climate drivers on Australian cotton production
Publisher: Elsevier BV
Date: 10-2022
Interbasin and interhemispheric impacts of a collapsed Atlantic Overturning Circulation
Publisher: Springer Science and Business Media LLC
Date: 06-2022
Reduced ENSO Variability due to a Collapsed Atlantic Meridional Overturning Circulation
Publisher: American Meteorological Society
Date: 15-08-2022
Abstract: Atlantic meridional overturning circulation (AMOC) collapses have punctuated Earth’s climate in the past, and future projections suggest a weakening and potential collapse in response to global warming and high-latitude ocean freshening. Among its most important teleconnections, the AMOC has been shown to influence El Niño–Southern Oscillation (ENSO), although there is no clear consensus on the tendency of this influence or the mechanisms at play. In this study, we investigate the effect of an AMOC collapse on ENSO by adding freshwater in the North Atlantic in a global climate model. The tropical Pacific mean-state changes caused by the AMOC collapse are found to alter the governing ENSO feedbacks, d ing the growth rate of ENSO. As a result, ENSO variability is found to decrease by ∼30% due to weaker air–sea coupling associated with a cooler tropical Pacific and an intensified Walker circulation. The decreased ENSO variability manifests in ∼95% less frequent extreme El Niño events and a shift toward more prevalent central Pacific El Niño than eastern Pacific El Niño events, marked by a reduced ENSO nonlinearity and asymmetry. These results provide mechanistic insights into the possible behavior of past and future ENSO in a scenario of a much weakened or collapsed AMOC. The Atlantic meridional overturning circulation (AMOC) has collapsed in the past and a future collapse due to greenhouse warming is a plausible scenario. An AMOC shutdown would have major ramifications for global climate, with extensive impacts on climate phenomena such as El Niño–Southern Oscillation (ENSO), which is the strongest source of year-to-year climate variability on the planet. Using numerical simulations, we show that an AMOC shutdown leads to weaker ENSO variability, manifesting in 95% reduction in extreme El Niño events, and a shift of the ENSO pattern toward the central Pacific. This study sheds light on the mechanisms behind these changes, with implications for interpreting past and future ENSO variability.
Pacific Equatorial Undercurrent: Mean state, sources, and future changes across models
Publisher: Frontiers Media SA
Date: 27-10-2012
DOI: 10.3389/FCLIM.2022.933091
Abstract: The Equatorial Undercurrent (EUC) stretches across the Pacific, transporting cool waters rich in oxygen and nutrients eastward to one of the most productive regions in the ocean. As an intricate part of the global climate system, EUC dynamics are essential to understanding future climate change but are poorly represented in global coupled climate models. This study examines EUC representation and future changes in the latest generations of the Coupled Model Intercomparison Project (CMIP6 and CMIP5) and an eddy-permitting ocean model. We also examine historical and projected changes in EUC source waters, including the Mindanao Current (MC), New Guinea Coastal Undercurrent (NGCU), and interior thermocline convergence. The circulation features in the models are broadly consistent with observations and ocean reanalyses, but improvements from CMIP5 to CMIP6 are limited. In the future projections, the EUC is enhanced in the western Pacific, with less prominent changes in CMIP6, but more so in the eddy-permitting model. The western Pacific EUC enhancement is likely associated with a wind-driven redirection of waters south of the equator, in which the NGCU boundary flow increases while the interior thermocline convergence decreases. This is superimposed on an overall weakening of the North Pacific subtropical overturning cell, including the MC, interior thermocline convergence, and Ekman ergence. As EUC heat and nutrient composition is linked to its sources, these projected changes have implications for the EUC's role in air–sea feedbacks, nutrient replenishment, and oxygen minimum zone ventilation in the eastern Pacific.
Enhanced climate instability in the North Atlantic and southern Europe during the Last Interglacial
Publisher: Springer Science and Business Media LLC
Date: 12-10-2018
DOI: 10.1038/S41467-018-06683-3
Abstract: Considerable ambiguity remains over the extent and nature of millennial/centennial-scale climate instability during the Last Interglacial (LIG). Here we analyse marine and terrestrial proxies from a deep-sea sediment sequence on the Portuguese Margin and combine results with an intensively dated Italian speleothem record and climate-model experiments. The strongest expression of climate variability occurred during the transitions into and out of the LIG. Our records also document a series of multi-centennial intra-interglacial arid events in southern Europe, coherent with cold water-mass expansions in the North Atlantic. The spatial and temporal fingerprints of these changes indicate a reorganization of ocean surface circulation, consistent with low-intensity disruptions of the Atlantic meridional overturning circulation (AMOC). The litude of this LIG variability is greater than that observed in Holocene records. Episodic Greenland ice melt and runoff as a result of excess warmth may have contributed to AMOC weakening and increased climate instability throughout the LIG.
The Impact of Interacting Climate Modes on East Australian Precipitation Moisture Sources
Publisher: American Meteorological Society
Date: 15-05-2022
Abstract: Modes of climate variability can drive significant changes to regional climate affecting extremes such as droughts, floods, and bushfires. The need to forecast these extremes and expected future increases in their intensity and frequency motivates a need to better understand the physical processes that connect climate modes to regional precipitation. Focusing on east Australia, where precipitation is driven by multiple interacting climate modes, this study provides a new perspective into the links between large-scale modes of climate variability and precipitation. Using a Lagrangian back-trajectory approach, we examine how El Niño–Southern Oscillation (ENSO) modifies the supply of evaporative moisture for precipitation, and how this is modulated by the Indian Ocean dipole (IOD) and southern annular mode (SAM). We demonstrate that La Niña modifies large-scale moisture transport together with local thermodynamic changes to facilitate local precipitation generation, whereas below-average precipitation during El Niño stems predominantly from increased regional subsidence. These dynamic–thermodynamic processes were often more pronounced during co-occurring La Niña/negative IOD and El Niño ositive IOD periods. As the SAM is less strongly correlated with ENSO, the impact of co-occurring ENSO and SAM largely depended on the state of ENSO. La Niña–related processes were exacerbated when combined with +SAM and d ened when combined with −SAM, and vice versa during El Niño. This new perspective on how interacting climate modes physically influence regional precipitation can help elucidate how model biases affect the simulation of Australian climate, facilitating model improvement and understanding of regional impacts from long-term changes in these modes. How climate modes modulate the oceanic and terrestrial sources of moisture for rainfall in east Australia is investigated. East Australia is wetter during La Niña because more moisture is transported into the region and is more easily turned into rainfall when it arrives, whereas drier conditions during El Niño are because local conditions inhibit the conversion of moisture into rainfall. Distant atmospheric changes over the Indian and Southern Oceans can intensify these changes. Our results can be used to better understand and predict the regional impact of long-term changes in these modes of climate variability, which are potentially altered under climate change.
Intermodel CMIP5 relationships in the baseline Southern Ocean climate system and with future projections
Publisher: Wiley
Date: 02-11-2020
Effect of anomalous warming in the central Pacific on the Australian monsoon
Publisher: American Geophysical Union (AGU)
Date: 06-2009
DOI: 10.1029/2009GL038416
The impact of the subtropical South Atlantic SST on South American precipitation
Publisher: Copernicus GmbH
Date: 10-11-2008
DOI: 10.5194/ANGEO-26-3457-2008
Abstract: Abstract. The Community Climate Model (CCM3) from the National Center for Atmospheric Research (NCAR) is used to investigate the effect of the South Atlantic sea surface temperature (SST) anomalies on interannual to decadal variability of South American precipitation. Two ensembles composed of multidecadal simulations forced with monthly SST data from the Hadley Centre for the period 1949 to 2001 are analysed. A statistical treatment based on signal-to-noise ratio and Empirical Orthogonal Functions (EOF) is applied to the ensembles in order to reduce the internal variability among the integrations. The ensemble treatment shows a spatial and temporal dependence of reproducibility. High degree of reproducibility is found in the tropics while the extratropics is apparently less reproducible. Austral autumn (MAM) and spring (SON) precipitation appears to be more reproducible over the South America-South Atlantic region than the summer (DJF) and winter (JJA) rainfall. While the Inter-tropical Convergence Zone (ITCZ) region is dominated by external variance, the South Atlantic Convergence Zone (SACZ) over South America is predominantly determined by internal variance, which makes it a difficult phenomenon to predict. Alternatively, the SACZ over western South Atlantic appears to be more sensitive to the subtropical SST anomalies than over the continent. An attempt is made to separate the atmospheric response forced by the South Atlantic SST anomalies from that associated with the El Niño – Southern Oscillation (ENSO). Results show that both the South Atlantic and Pacific SSTs modulate the intensity and position of the SACZ during DJF. Particularly, the subtropical South Atlantic SSTs are more important than ENSO in determining the position of the SACZ over the southeast Brazilian coast during DJF. On the other hand, the ENSO signal seems to influence the intensity of the SACZ not only in DJF but especially its oceanic branch during MAM. Both local and remote influences, however, are confounded by the large internal variance in the region. During MAM and JJA, the South Atlantic SST anomalies affect the magnitude and the meridional displacement of the ITCZ. In JJA, the ENSO has relatively little influence on the interannual variability of the simulated rainfall. During SON, however, the ENSO seems to counteract the effect of the subtropical South Atlantic SST variations on convection over South America.
Revisiting remote drivers of the 2014 drought in South-Eastern Brazil
Publisher: Springer Science and Business Media LLC
Date: 03-09-2020
DOI: 10.1007/S00382-020-05442-9
Abstract: South-Eastern Brazil experienced a devastating drought associated with significant agricultural losses in austral summer 2014. The drought was linked to the development of a quasi-stationary anticyclone in the South Atlantic in early 2014 that affected local precipitation patterns over South-East Brazil. Previous studies have suggested that the unusual blocking was triggered by tropical Pacific sea surface temperature (SST) anomalies and, more recently, by convection over the Indian Ocean related to the Madden–Julian Oscillation. Further investigation of the proposed teleconnections appears crucial for anticipating future economic impacts. In this study, we use numerical experiments with an idealized atmospheric general circulation model forced with the observed 2013/2014 SST anomalies in different ocean basins to understand the dominant mechanism that initiated the 2014 South Atlantic anticyclonic anomaly. We show that a forcing with global 2013/2014 SST anomalies enhances the chance for the occurrence of positive geopotential height anomalies in the South Atlantic. However, further sensitivity experiments with SST forcings in separate ocean basins suggest that neither the Indian Ocean nor tropical Pacific SST anomalies alone have contributed significantly to the anomalous atmospheric circulation that led to the 2014 South-East Brazil drought. The model study rather points to an important role of remote forcing from the South Pacific, local South Atlantic SSTs, and internal atmospheric variability in driving the persistent blocking over the South Atlantic.
From severe droughts in South America to marine heatwaves in the South Atlantic
Publisher: Copernicus GmbH
Date: 07-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-5162
Abstract: & & In 2013/14 eastern South America experienced one of its worst droughts, leading to water shortages in S& #227 o Paulo, the world& #8217 s fourth most populated city. This event was also responsible for a dengue fever outbreak that tripled the usual number of fatalities and reduced Brazilian coffee production leading to a global shortages and worldwide price increases. The drought was associated with an anomalous anticyclonic circulation off southeast South America that prevented synoptic systems reaching the region while inhibiting the development of the South Atlantic Convergence Zone and its associated rainfall. A concomitant and unprecedented marine heatwave also developed in the southwest Atlantic. Here we show from observations that such droughts and adjacent marine heatwaves have a common remote cause. Atmospheric blocking triggered by tropical convection in the Indian and Pacific oceans can cause persistent anticyclonic circulation that not only leads to severe drought but also generates marine heatwaves in the adjacent ocean. We show that increased shortwave radiation due to reduced cloud cover and reduced ocean heat loss from weaker winds are the main contributors to the establishment of marine heatwaves in the region. The proposed mechanism, which involves droughts, extreme air temperature over land and atmospheric blocking explains approximately 60% of the marine heatwave events in the western South Atlantic. We also identified an increase in frequency, duration, intensity and extension of marine heatwave events over the satellite period 1982& #8211 . Moreover, surface primary production was reduced during these events with implications for regional fisheries.& &
Evaluation of seasonal teleconnections to remote drivers of Australian rainfall in CMIP5 and CMIP6 models
Publisher: CSIRO Publishing
Date: 2023
DOI: 10.1071/ES23002
Land-sea temperature contrasts at the Last Interglacial and their impact on the hydrological cycle
Publisher: Copernicus GmbH
Date: 21-04-2021
Abstract: Abstract. Due to different orbital configurations, high northern latitude summer insolation was higher during the Last Interglacial period (LIG 129–116 thousand years before present, ka) than during the pre-industrial period (PI), while high southern latitude summer insolation was lower. The climatic response to these changes is studied here with focus on the Southern Hemisphere monsoons, by performing an equilibrium experiment of the LIG at 127 ka with the Australian Earth System Model, ACCESS-ESM1.5, as part of the Paleoclimate Model Intercomparison Project 4 (PMIP4). Simulated mean surface air temperature between 40 and 60∘ N over land during boreal summer is 6.5 ∘C higher at the LIG compared to PI, which leads to a northward shift of the Intertropical Convergence Zone (ITCZ) and a strengthening of the North African and Indian monsoons. Despite 0.4 ∘C cooler conditions in austral summer in the Southern Hemisphere (0–90∘ S), annual mean air temperatures are 1.2 ∘C higher at southern mid-latitudes to high latitudes (40–80∘ S). These differences in temperature are coincident with a large-scale reorganisation of the atmospheric circulation. The ITCZ shifts southward in the Atlantic and Indian sectors during the LIG austral summer compared to PI, leading to increased precipitation over the southern tropical oceans. However, weaker Southern Hemisphere insolation during LIG austral summer induces a significant cooling over land, which in turn weakens the land–sea temperature contrast, leading to an overall reduction (−20 %) in monsoonal precipitation over the Southern Hemisphere's continental regions compared to PI. The intensity and areal extent of the Australian, South American and South African monsoons are consistently reduced in LIG. This is associated with greater pressure and subsidence over land due to a strengthening of the Southern Hemisphere Hadley cell during austral summer.
Resolution dependence of the simulated precipitation and diurnal cycle over the Maritime Continent
Publisher: Springer Science and Business Media LLC
Date: 19-08-2016
Can Indian Ocean SST anomalies influence South American rainfall?
Publisher: Springer Science and Business Media LLC
Date: 20-08-2011
Phase Coherence Between Surrounding Oceans Enhances Precipitation Shortages in Northeast Brazil
Publisher: American Geophysical Union (AGU)
Date: 28-04-2022
DOI: 10.1029/2021GL097647
Abstract: Understanding the direct and indirect impact of the Pacific and Atlantic Oceans on precipitation in the region of Northeast Brazil (NEB) is crucial for monitoring unprecedented drought events. We propose nonlinear methods of phase coherence and generalized event synchronization analysis to understand the underlying mechanism. In particular, the relationships between sea surface temperature (SST) variability and the standard precipitation index are interpreted as direct interactions, while the relationships between surrounding oceans are interpreted as indirect effects on the precipitation. Our results reveal a dominant role of tropical North Atlantic for precipitation deficit and droughts, particularly in recent decades. Meanwhile, the indirect Pacific‐North Atlantic phase synchronizations have significant influence on and reinforcement of the droughts in NEB. Furthermore, we find that the instantaneous angular frequencies of precipitation and SST are drastically changed after very strong El Niño and La Niña events, therefore resulting in a higher probability of phase coherence.
Non-linearity in the pathway of El Niño-Southern Oscillation to the tropical North Atlantic
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-7483
Abstract: & & El Ni& #241 o-Southern Oscillation can influence the Tropical North Atlantic (TNA), leading to anomalous sea surface temperatures (SST) at a lag of several months. Several mechanisms have been proposed to explain this teleconnection. These mechanisms include both tropical and extratropical pathways, contributing to anomalous trade winds and static stability over the TNA region. The TNA SST response to ENSO has been suggested to be nonlinear. Yet the overall linearity of the ENSO-TNA teleconnection via the two pathways remains unclear. Here we use reanalysis data to confirm that the SST anomaly (SSTA) in the TNA is nonlinear with respect to the strength of the SST forcing in the tropical Pacific, as further increases in El Ni& #241 o magnitudes cease to create further increases of the TNA SSTA. We further show that the tropical pathway is more linear than the extratropical pathway by sub- iding the inter-basin connection into extratropical and tropical pathways. The extratropical pathway is modulated by the North Atlantic Oscillation (NAO) and the location of the SSTA in the Pacific, but this modulation insufficiently explains the nonlinearity in TNA SSTA. As neither extratropical nor tropical pathways can explain the nonlinearity, this suggests that external factors are at play. Further analysis shows that the TNA SSTA is highly influenced by the preconditioning of the tropical Atlantic SST. This preconditioning is found to be associated with the NAO through SST-tripole patterns.& &
Negative Indian Ocean Dipole drives groundwater recharge in southeast Australia
Publisher: Research Square Platform LLC
Date: 25-05-2023
DOI: 10.21203/RS.3.RS-2755505/V2
Abstract: Understanding how Australian groundwater recharge is affected by the Pacific and Indian Ocean climate drivers is crucial for water resource planning and management, especially in semi-arid environments. This will allow for assessment of the impact of climate change on the occurrence and timing of groundwater recharge and the sustainable management of this resource into the future. Measuring groundwater recharge is difficult as it occurs in the subsurface. However, caves situated in the unsaturated zone give us the opportunity to observe these subsurface processes. Here we show good agreement between the recharge events measured in a cave system and groundwater bores at a nearby site. We also show that the most significant recharge event during a decade of observations occurred during a particularly strong negative Indian Ocean Dipole period. Through further analysis of recharge events dating back 1900 we show for the first time a significant link with negative Indian Ocean Dipole events.
Coupled Feedbacks From the Tropical Pacific to the Atlantic Meridional Overturning Circulation
Publisher: American Geophysical Union (AGU)
Date: 19-10-2023
DOI: 10.1029/2023GL103250
Warming of the Indian Ocean weakens the Atlantic Niño - El Niño Southern Oscillation connection 
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-13911
Abstract: & & The tropical Indian Ocean has warmed by 1 degree Celsius since the mid-twentieth century. This warming is likely to continue as the atmospheric carbon dioxide levels keep rising. Here, we discuss how the warming trend could influence the El Ni& #241 o Southern Oscillation (ENSO) via interaction with the Pacific and the Atlantic Ocean mean state and variability. The warming trend leads to the strengthening of easterlies in the western equatorial Pacific, subsequent downwelling and increase of the mixed later depth in the west, and an increase in the subsurface temperature gradient across the equatorial Pacific. In the eastern equatorial Pacific, the response of upwelling ocean currents to surface wind stress decreases, resulting in a weakening of ENSO litude. The Indian Ocean warming influences ENSO via the Atlantic Ocean as well. There, it is associated with the strengthening of equatorial easterly winds, and anomalous warming in the west and upwelling induced cooling in the east, especially in austral winter, during the peak of the Atlantic Ni& #241 o. Consequently, this results in a decrease of the litude of Atlantic Ni& #241 o events and weakening of the Atlantic Ni& #241 o-ENSO teleconnection, thereby hindering the transition of El Ni& #241 o events to La Ni& #241 a events. Thus, the Indian Ocean warming trend is found to modulate tropical Pacific and Atlantic mean state and variability, with implications for ENSO predictability under a warming climate.& &
Negative Indian Ocean Dipole drives groundwater recharge in southeast Australia
Publisher: Research Square Platform LLC
Date: 22-05-2023
DOI: 10.21203/RS.3.RS-2755505/V1
Abstract: Understanding how Australian groundwater recharge is affected by the Pacific and Indian Ocean climate drivers is crucial for water resource planning and management, especially in semi-arid environments. This will allow for assessment of the impact of climate change on the occurrence and timing of groundwater recharge and the sustainable management of this resource into the future. Measuring groundwater recharge is difficult as it occurs in the subsurface. However, caves situated in the unsaturated zone give us the opportunity to observe these subsurface processes. Here we show good agreement between the recharge events measured in a cave system and groundwater bores at a nearby site. We also show that the most significant recharge event during a decade of observations occurred during a particularly strong negative Indian Ocean Dipole period. Through further analysis of recharge events dating back 1900 we show for the first time a significant link with negative Indian Ocean Dipole events.
Temperature and precipitation responses to El Niño-Southern Oscillation in a hierarchy of datasets with different levels of observational constraints
Publisher: Springer Science and Business Media LLC
Date: 07-08-2020
Mechanisms of tropical Pacific decadal variability
Publisher: Springer Science and Business Media LLC
Date: 18-10-2023
Projected changes to South Atlantic boundary currents and confluence region in the CMIP5 models: the role of wind and deep ocean changes
Publisher: IOP Publishing
Date: 09-2016
Weak Southern Hemispheric monsoons during the Last Interglacial period
Publisher: Copernicus GmbH
Date: 25-11-2020
DOI: 10.5194/CP-2020-149
Abstract: Abstract. Due to different orbital configurations, high northern latitude boreal summer insolation was higher during the Last Interglacial period (LIG 129–116 thousand years before present, ka) than during the preindustrial period (PI), while high southern latitude austral summer insolation was lower. The climatic response to these changes is studied here with focus on the southern hemispheric monsoons, by performing an equilibrium experiment of the LIG at 127 ka with the Australian Earth System Model, ACCESS-ESM1.5, as part of the Paleoclimate Model Intercomparison Project 4 (PMIP4). In our simulation, mean surface air temperature increases by 6.5 °C over land during boreal summer between 40° N and 60° N in the LIG compared to PI, leading to a northward shift of the Inter-Tropical Convergence Zone (ITCZ) and a strengthening of the North African and Indian monsoons. Despite 0.4 °C cooler conditions in austral summer in the Southern Hemisphere (0–90° S), annual mean air temperatures are 1.2 °C higher at southern mid-to-high latitudes (40° S–80° S). These differences in temperature are coincident with a large-scale reorganisation of the atmospheric circulation. The ITCZ shifts southward in the Atlantic and Indian sectors during the LIG austral summer compared to PI, leading to increased precipitation over the southern tropical oceans. However, the decline in Southern Hemisphere insolation during austral summer induces a significant cooling over land, which in turn weakens the land-sea temperature contrast, leading to an overall reduction (−20 %) in monsoonal precipitation over the Southern Hemisphere's continental regions. The intensity and areal extent of the Australian, South American and South African monsoons are consistently reduced. This is associated with greater pressure and subsidence over land due to a strengthening of the southern hemispheric Hadley cell during austral summer.
Indian Ocean warming modulates global atmospheric circulation trends
Publisher: Springer Science and Business Media LLC
Date: 19-07-2020
Weather and Climate Extremes: Current Developments
Publisher: MDPI AG
Date: 25-12-2019
Abstract: An increasing number of extreme events have been observed around the world over the past few decades, some of them attributed to global warming [...]
What causes southeast Australia's worst droughts?
Publisher: American Geophysical Union (AGU)
Date: 02-2009
DOI: 10.1029/2008GL036801
What Determines the Lagged ENSO Response in the South‐West Indian Ocean?
Publisher: American Geophysical Union (AGU)
Date: 24-03-2021
DOI: 10.1029/2020GL091958
Abstract: Oceanic Rossby waves can propagate climate signals over considerable distances over long timescales. Using a long simulation from a coupled climate model, we examine oceanic and mixed atmosphere‐ocean teleconnections to the south‐western Indian Ocean (SWIO) associated with Rossby waves excited by the El Niño‐Southern Oscillation (ENSO). Reconstruction of propagating ENSO‐induced sea‐level anomalies from the simulation using an optimized linear wave model with dissipation highlights the prominent role of baroclinic, rather than barotropic, Rossby waves in modulating sea‐surface heights. Between 9.5° and 18.5°S, El Niño‐associated anomalous anticyclonic wind‐stress fields initiate downwelling Rossby waves, potentially influencing SWIO regional climate around 1–4 seasons after El Niño peak, while also destructively interfering with upwelling waves triggered on the eastern boundary by oceanic teleconnections. Further south, weaker ENSO winds, dissipation, non‐linear processes, and interference from higher‐mode Rossby waves limit ENSO influences in the SWIO. In the model, ENSO‐associated predictability is therefore constrained by the “atmospheric” rather than “oceanic” bridge.
Sensitivity of South American summer rainfall to tropical Pacific Ocean SST anomalies
Publisher: American Geophysical Union (AGU)
Date: 05-01-2011
DOI: 10.1029/2010GL045571
Northward ITCZ shift drives reduced ENSO activity in the Mid-Pliocene Warm Period
Publisher: Research Square Platform LLC
Date: 22-06-2021
DOI: 10.21203/RS.3.RS-402220/V1
Abstract: The El Niño Southern Oscillation (ENSO) is the strongest pattern of year-to-year climate variability found in the equatorial Pacific Ocean with global impacts. However, it is not fully understood how ENSO responds to different warming scenarios. In the warmer climate (~2-3K) of the mid-Pliocene Warm Period (~3 Ma BP), models consistently suggest a weakening of ENSO variability, with a mean reduction of 25% (±16%). We show that a near unanimous weakening of ENSO across models cannot be fully explained simply by mean state changes in the equatorial Pacific Ocean. Instead, robust off-equatorial mean state changes in the mid-Pliocene are not favourable for ENSO activity. A northward displacement of the Pacific Inter-Tropical Convergence Zone (ITCZ) is found to be significantly linked to the ENSO weakening across models. This is accompanied by increased south-easterly trade winds in the western Pacific and an intensified South Pacific Subtropical High, which are consistent with suppressed activity of processes that initiate ENSO. Our results provide a constraint to past and future changes to ENSO associated with the climatological ITCZ position.
Evaluation of monsoon seasonality and the tropospheric biennial oscillation transitions in the CMIP models
Publisher: American Geophysical Union (AGU)
Date: 26-10-2012
DOI: 10.1029/2012GL053322
Supplementary material to "Weak Southern Hemispheric monsoons during the Last Interglacial period"
Publisher: Copernicus GmbH
Date: 25-11-2020
Erratum
Publisher: Springer Science and Business Media LLC
Date: 11-2004
Indian Ocean Dipole in CMIP5 and CMIP6: characteristics, biases, and links to ENSO
Publisher: Springer Science and Business Media LLC
Date: 13-07-2020
DOI: 10.1038/S41598-020-68268-9
Abstract: Accurately representing the Indian Ocean Dipole (IOD) is crucial for reliable climate predictions and future projections. However, El Niño-Southern Oscillation (ENSO) and IOD interact, making it necessary to evaluate ENSO and IOD simultaneously. Using the historical simulation from 32 fifth phase of Coupled Model Intercomparison Project (CMIP5) models and 34 CMIP6 models, here we find that there are some modest changes in the basic characteristics of the IOD and ENSO from CMIP5 to CMIP6. Firstly, there is a slight shift in the seasonality of IOD toward an earlier peak in September in CMIP6, from November in CMIP5. Secondly, inter-model spread in the frequency of ENSO and the IOD has reduced in CMIP6 relative to CMIP5. ENSO asymmetry is still underestimated in CMIP6, based on the skewness of the Niño3 index, while the IOD skewness has degraded from CMIP5. Finally, mean state SST biases impact on the strength of the IOD the Pacific cold tongue mean state is important in CMIP5, but in CMIP6 the Pacific warm pool mean state is more important.
Reproducibility of South American Precipitation due to Subtropical South Atlantic SSTs
Publisher: American Meteorological Society
Date: 15-06-2008
Abstract: This work investigates the reproducibility of precipitation simulated with an atmospheric general circulation model (AGCM) forced by subtropical South Atlantic sea surface temperature (SST) anomalies. This represents an important test of the model prior to investigating the impact of SSTs on regional climate. A five-member ensemble run was performed using the National Center for Atmospheric Research (NCAR) Community Climate Model, version 3 (CCM3). The CCM3 was forced by observed monthly SST over the South Atlantic from 20° to 60°S. The SST dataset used is from the Hadley Centre covering the period of September 1949–October 2001 this covers more than 50 yr of simulation. A statistical technique is used to determine the reproducibility in the CCM3 runs and to assess potential predictability in precipitation. Empirical orthogonal function analysis is used to reconstruct the ensemble using the most reproducible forced modes in order to separate the atmospheric response to local SST forcing from its internal variability. Results for reproducibility show a seasonal dependence, with higher values during austral autumn and spring. The spatial distribution of reproducibility shows that the tropical atmosphere is dominated by the underlying SSTs while variations in the subtropical–extratropical regions are primarily driven by internal variability. As such, changes in the South Atlantic convergence zone (SACZ) region are mainly dominated by internal atmospheric variability while the ITCZ has greater external dependence, making it more predictable. The reproducibility distribution reveals increased values after the reconstruction of the ensemble.
The influence of Southern Hemisphere sea‐ice extent on the latitude of the mid‐latitude jet stream
Publisher: American Geophysical Union (AGU)
Date: 08-2011
DOI: 10.1029/2011GL048056
Obliquity control on Southern Hemisphere climate during the last glacial
Publisher: Springer Science and Business Media LLC
Date: 26-06-2015
DOI: 10.1038/SREP11673
Abstract: Recent paleoclimate reconstructions have challenged the traditional view that Northern Hemisphere insolation and associated feedbacks drove synchronous global climate and ice-sheet volume during the last glacial cycle. Here we focus on the response of the Patagonian Ice Sheet and demonstrate that its maximum expansion culminated at 28,400 ± 500 years before present (28.4 ± 0.5 ka), more than 5,000 years before the minima in 65°N summer insolation and the formally-defined Last Glacial Maximum (LGM) at 21,000 ± 2,000 years before present. To investigate the potential drivers of this early LGM (eLGM), we simulate the effects of orbital changes using a suite of climate models incorporating prescribed and evolving sea-ice anomalies. Our analyses suggest that Antarctic sea-ice expansion at 28.5 ka altered the location and intensity of the Southern Hemisphere storm track, triggering regional cooling over Patagonia of 5°C that extends across the wider mid-southern latitudes. In contrast, at the LGM, continued sea-ice expansion reduced regional temperature and precipitation further, effectively starving the ice sheet and resulting in reduced glacial expansion. Our findings highlight the dominant role that orbital changes can play in driving Southern Hemisphere glacial climate via the sensitivity of mid-latitude regions to changes in Antarctic sea-ice extent.
Increasing dominance of Indian Ocean variability impacts Australian wheat yields
Publisher: Springer Science and Business Media LLC
Date: 13-10-2022
Impacts of the tropical trans-basin variability on Australian rainfall
Publisher: Springer Science and Business Media LLC
Date: 22-10-2016
Australian Monsoon Variability Driven by a Gill–Matsuno-Type Response to Central West Pacific Warming
Publisher: American Meteorological Society
Date: 15-09-2010
Abstract: The objective of this study is to investigate the mechanisms that cause the anomalous intensification of tropical Australian rainfall at the height of the monsoon during El Niño Modoki events. In such events, northwestern Australia tends to be wetter in January and February when the SST warming is displaced to the central west Pacific, the opposite response to that associated with a traditional El Niño. In addition, during the bounding months, that is, December and March, there is below-average rainfall induced by an anomalous Walker circulation. This behavior tends to narrow and intensify the annual rainfall cycle over northwestern Australia relative to the climatology, causing a delayed monsoonal onset and an earlier retreat over the region. Observational datasets and numerical experiments with a general circulation model are used to examine the atmospheric response to the central west Pacific SST warming. It is shown here that the increase of precipitation, particularly in February, is phased locked to the seasonal cycle when the intertropical convergence zone is displaced southward and the South Pacific convergence zone is strengthened. An interaction between the interannual SST variability associated with El Niño Modoki events and the evolution of the seasonal cycle intensifies deep convection in the central west Pacific, driving a Gill–Matsuno-type response to the diabatic heating. The westward-propagating disturbance associated with the Gill–Matsuno mechanism generates an anomalous cyclonic circulation over northwestern Australia, leading to convergence of moisture and increased precipitation. The Gill–Matsuno-type response overwhelms the subsidence of the anomalous Walker circulation associated with Modoki events over Australia during the peak of the monsoon.
Projected slow down of South Indian Ocean circulation
Publisher: Springer Science and Business Media LLC
Date: 27-11-2019
DOI: 10.1038/S41598-019-54092-3
Abstract: Using an ensemble of 28 climate models, we examine hindcasts and ‘business as usual’ future changes to large-scale South Indian Ocean dynamics. We compare model ensemble seasonal-to-annual volume transports to observations and explore drivers of past and future circulation variability and change. Off the west coast of Australia, models consistently project a weakening of the Leeuwin Current and Undercurrent due to reduced onshore flow and downwelling. The reduced onshore flow is related to changes in the alongshore pressure gradient. While the alongshore pressure gradient change is consistent with the Indonesian Throughflow projected weakening, we found no inter-model relationship between these changes. In the south-western Indian Ocean, the models project a robust weakening of the North East and South East Madagascar Currents, Agulhas Current and transport through the Mozambique Channel. This reduced Indian Ocean western boundary flow is partly associated with a weaker Indonesian Throughflow and overturning circulation, where the latter is related to a decrease in the convergence of deep Southern Ocean waters into the Indian Ocean. In contrast to the weakening of other features, the westward flowing Agulhas Current extension south of Africa is projected to strengthen, which is consistent with an intensification of the Antarctic Circumpolar Current.
El Niño Modoki Impacts on Australian Rainfall
Publisher: American Meteorological Society
Date: 06-2009
Abstract: This study investigates interseasonal and interevent variations in the impact of El Niño on Australian rainfall using available observations from the postsatellite era. Of particular interest is the difference in impact between classical El Niño events wherein peak sea surface temperature (SST) anomalies appear in the eastern Pacific and the recently termed El Niño “Modoki” events that are characterized by distinct warm SST anomalies in the central Pacific and weaker cold anomalies in the west and east of the basin. A clear interseasonal and interevent difference is apparent, with the maximum rainfall response for Modoki events occurring in austral autumn compared to austral spring for classical El Niños. Most interestingly, the Modoki and non-Modoki El Niño events exhibit a marked difference in rainfall impact over Australia: while classical El Niños are associated with a significant reduction in rainfall over northeastern and southeastern Australia, Modoki events appear to drive a large-scale decrease in rainfall over northwestern and northern Australia. In addition, rainfall variations during March–April–May are more sensitive to the Modoki SST anomaly pattern than the conventional El Niño anomalies to the east.
The Contribution of Indian Ocean Sea Surface Temperature Anomalies on Australian Summer Rainfall during El Niño Events
Publisher: American Meteorological Society
Date: 15-07-2011
Abstract: This study investigates the impact of Indian Ocean sea surface temperature (SST) anomalies on the atmospheric circulation of the Southern Hemisphere during El Niño events, with a focus on Australian climate. During El Niño episodes, the tropical Indian Ocean exhibits two types of SST response: a uniform “basinwide warming” and a dipole mode—the Indian Ocean dipole (IOD). While the impacts of the IOD on climate have been extensively studied, the effects of the basinwide warming, particularly in the Southern Hemisphere, have received less attention. The interannual basinwide warming response has important implications for Southern Hemisphere atmospheric circulation because 1) it accounts for a greater portion of the Indian Ocean monthly SST variance than the IOD pattern and 2) its maximum litude occurs during austral summer to early autumn, when large parts of Australia, South America, and Africa experience their monsoon. Using observations and numerical experiments with an atmospheric general circulation model forced with historical SST from 1949 to 2005 over different tropical domains, the authors show that the basinwide warming leads to a Gill–Matsuno-type response that reinforces the anomalies caused by changes in the Pacific as part of El Niño. In particular, the basinwide warming drives strong subsidence over Australia, prolonging the dry conditions during January–March, when El Niño–related SST starts to decay. In addition to the anomalous circulation in the tropics, the basinwide warming excites a pair of barotropic anomalies in the Indian Ocean extratropics that induces an anomalous anticyclone in the Great Australian Bight.
CORRIGENDUM
Publisher: American Meteorological Society
Date: 12-2013
Future changes to the upper ocean Western Boundary Currents across two generations of climate models
Publisher: Springer Science and Business Media LLC
Date: 05-05-2021
DOI: 10.1038/S41598-021-88934-W
Abstract: Western Boundary Currents (WBCs) are important for the oceanic transport of heat, dissolved gases and nutrients. They can affect regional climate and strongly influence the dispersion and distribution of marine species. Using state-of-the-art climate models from the latest and previous Climate Model Intercomparison Projects , we evaluate upper ocean circulation and examine future projections, focusing on subtropical and low-latitude WBCs. Despite their coarse resolution, climate models successfully reproduce most large-scale circulation features with ensemble mean transports typically within the range of observational uncertainty, although there is often a large spread across the models and some currents are systematically too strong or weak. Despite considerable differences in model structure, resolution and parameterisations, many currents show highly consistent projected changes across the models. For ex le, the East Australian Current, Brazil Current and Agulhas Current extensions are projected to intensify, while the Gulf Stream, Indonesian Throughflow and Agulhas Current are projected to weaken. Intermodel differences in most future circulation changes can be explained in part by projected changes in the large-scale surface winds. In moving to the latest model generation, despite structural model advancements, we find little systematic improvement in the simulation of ocean transports nor major differences in the projected changes.
Multi-decadal modulation of the El Niño–Indian monsoon relationship by Indian Ocean variability
Publisher: IOP Publishing
Date: 07-2011
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