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1
Ummenhofer, Caroline C., Peter C. McIntosh, Michael J. Pook, and James S. Risbey. "Impact of Surface Forcing on Southern Hemisphere Atmospheric Blocking in the Australia–New Zealand Sector." Journal of Climate 26, no. 21 (October 16, 2013): 8476–94. http://dx.doi.org/10.1175/jcli-d-12-00860.1.
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Abstract Characteristics of atmospheric blocking in the Southern Hemisphere (SH) are explored in atmospheric general circulation model (AGCM) simulations with the Community Atmosphere Model, version 3, with a particular focus on the Australia–New Zealand sector. Preferred locations of blocking in SH observations and the associated seasonal cycle are well represented in the AGCM simulations, but the observed magnitude of blocking is underestimated throughout the year, particularly in late winter and spring. This is related to overly zonal flow due to an enhanced meridional pressure gradient in the model, which results in a decreased amplitude of the longwave trough/ridge pattern. A range of AGCM sensitivity experiments explores the effect on SH blocking of tropical heating, midlatitude sea surface temperatures, and land–sea temperature gradients created over the Australian continent during austral winter. The combined effects of tropical heating and extratropical temperature gradients are further explored in a configuration that is favorable for blocking in the Australia–New Zealand sector with warm SST anomalies to the north of Australia, cold to the southwest of Australia, warm to the southeast, and cool Australian land temperatures. The blocking-favorable configuration indicates a significant strengthening of the subtropical jet and a reduction in midlatitude flow, which results from changes in the thermal wind. While these overall changes in mean climate, predominantly forced by the tropical heating, enhance blocking activity, the magnitude of atmospheric blocking compared to observations is still underestimated. The blocking-unfavorable configuration with surface forcing anomalies of opposite sign results in a weakening subtropical jet, enhanced midlatitude flow, and significantly reduced blocking.
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Hudson, D., A. G. Marshall, O. Alves, G. Young, D. Jones, and A. Watkins. "Forewarned is Forearmed: Extended-Range Forecast Guidance of Recent Extreme Heat Events in Australia." Weather and Forecasting 31, no. 3 (April 29, 2016): 697–711. http://dx.doi.org/10.1175/waf-d-15-0079.1.
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Abstract There has been increasing demand in Australia for extended-range forecasts of extreme heat events. An assessment is made of the subseasonal experimental guidance provided by the Bureau of Meteorology’s seasonal prediction system, Predictive Ocean Atmosphere Model for Australia (POAMA, version 2), for the three most extreme heat events over Australia in 2013, which occurred in January, March, and September. The impacts of these events included devastating bushfires and damage to crops. The outlooks performed well for January and September, with forecasts indicating increased odds of top-decile maximum temperature over most affected areas at least one week in advance for the fortnightly averaged periods at the start of the heat waves and for forecasts of the months of January and September. The March event was more localized, affecting southern Australia. Although the anomalously high sea surface temperature around southern Australia in March (a potential source of predictability) was correctly forecast, the forecast of high temperatures over the mainland was restricted to the coastline. September was associated with strong forcing from some large-scale atmospheric climate drivers known to increase the chance of having more extreme temperatures over parts of Australia. POAMA-2 was able to forecast the sense of these drivers at least one week in advance, but their magnitude was weaker than observed. The reasonably good temperature forecasts for September are likely due to the model being able to forecast the important climate drivers and their teleconnection to Australian climate. This study adds to the growing evidence that there is significant potential to extend and augment traditional weather forecast guidance for extreme events to include longer-lead probabilistic information.
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Ummenhofer, Caroline C., Alexander Sen Gupta, Andréa S. Taschetto, and Matthew H. England. "Modulation of Australian Precipitation by Meridional Gradients in East Indian Ocean Sea Surface Temperature." Journal of Climate 22, no. 21 (November 1, 2009): 5597–610. http://dx.doi.org/10.1175/2009jcli3021.1.
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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.
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Gilmore, Stephen. "Lyapunov Exponents and Temperature Transitions in a Warming Australia." Journal of Climate 32, no. 10 (April 30, 2019): 2969–89. http://dx.doi.org/10.1175/jcli-d-18-0015.1.
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Abstract Multiple potential tipping points in the Earth system that involve alternative states have been identified that are susceptible to anthropogenic forcing. Past events—from millions of years ago to within the last century—have manifest as abrupt changes in climatic indicators such as the temperature record. Recent unprecedented heat waves in Australia, their associated devastation, and the considerations above provide motivation to ask whether the Australian daily maximum temperature record has been subject to such abrupt changes. Using a new diagnostic tool—the Lyapunov plot—here it is shown that multiple temperature transitions have occurred with respect to the maximum daily temperature record in widely separated locations in Australia over the last 150 years. All maximum Lyapunov exponents are positive in sign, indicating that the transitions are chaos-to-chaos transitions, and that the different climate modes identified are likely to be manifestations of distinct chaotic attractors. Many of these events occur simultaneously with transitions or extremes in the major natural cycles affecting Australia’s climate, but this observation is not universal. It is known that chaos-to-chaos transitions can result in changes in the value(s) of the state variable(s) that can range from subtle to severe. Although the identified transitions are not catastrophic, this observation does not rule out the possibility of severe, unprecedented, and discontinuous increases in average daily maximum temperatures occurring in Australia at any time within the next few decades.
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Hendon, Harry H., David W. J. Thompson, and Matthew C. Wheeler. "Australian Rainfall and Surface Temperature Variations Associated with the Southern Hemisphere Annular Mode." Journal of Climate 20, no. 11 (June 1, 2007): 2452–67. http://dx.doi.org/10.1175/jcli4134.1.
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Abstract Daily variations in Australian rainfall and surface temperature associated with the Southern Hemisphere annular mode (SAM) are documented using observations for the period 1979–2005. The high index polarity of the SAM is characterized by a poleward contraction of the midlatitude westerlies. During winter, the high index polarity of the SAM is associated with decreased daily rainfall over southeast and southwest Australia, but during summer it is associated with increased daily rainfall on the southern east coast of Australia and decreased rainfall in western Tasmania. Variations in the SAM explain up to ∼15% of the weekly rainfall variance in these regions, which is comparable to the variance accounted for by the El Niño–Southern Oscillation, especially during winter. The most widespread temperature anomalies associated with the SAM occur during the spring and summer seasons, when the high index polarity of the SAM is associated with anomalously low maximum temperature over most of central/eastern subtropical Australia. The regions of decreased maximum temperature are also associated with increased rainfall. Implications for recent trends in Australian rainfall and temperature are discussed.
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Tihema, Tamika. "Seasonal climate summary for the southern hemisphere (summer 2017–18): an exceptionally warm season for Australia – a short-lived and weak La Niña." Journal of Southern Hemisphere Earth Systems Science 69, no. 1 (2019): 351. http://dx.doi.org/10.1071/es19018.
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This is a summary of the southern hemisphere atmospheric circulation patterns and meteorological indices for summer 2017–18; an account of seasonal rainfall and temperature for the Australian region is also provided. A short-lived and weak La Niña developed but decayed by the end of February 2018. Sea-surface temperatures were exceptionally warm in the Tasman Sea from late 2017 to early 2018. It was an exceptionally warm summer for Australia, and the third-warmest mean temperature on record for the nation. Summer rainfall was close to the long-term average for Australia, with aboveaverage rainfall in west and below-average rainfall in the east.
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Lee, S. Y., and T. Y. Koh. "Teleconnection between Australian winter temperature and Indian summer monsoon rainfall." Atmospheric Chemistry and Physics 12, no. 2 (January 16, 2012): 669–81. http://dx.doi.org/10.5194/acp-12-669-2012.
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Abstract. The pattern of evaporative sources and the direction of the large-scale circulation over the Indian Ocean during the boreal summer raises the question of whether atmospheric conditions in Australia could influence conditions over the Indian subcontinent, despite the long passage of air over the Indian Ocean. The authors propose that such an influence is sometimes possible when there is unusually low temperature over inland Australia during the austral winter, through the mechanism where such a temperature extreme enhances evaporation rate over the eastern tropical Indian Ocean and hence enhances rainfall over two regions in western India after 13–19 days. Results from trajectory calculations indicate that such an influence is mechanistically feasible, with air of Australian origin contributing 0.5–1.5% of the climatological net precipitation for monsoon seasonal rainfall over western India. Statistics performed on reanalysis, satellite and in situ data are consistent with such a mechanism. Since extreme winter temperature in Australia is often associated with cold-air outbreaks, the described mechanism may be an example of how southern hemispheric mid-latitude weather can influence northern hemispheric monsoon rainfall. Further study is recommended through modelling and comparison with various known causes of atmospheric variability to confirm the existence of such a mechanism and determine the extent of its influence during specific low temperature episodes.
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van Rensch, Peter, and Wenju Cai. "Indo-Pacific–Induced Wave Trains during Austral Autumn and Their Effect on Australian Rainfall." Journal of Climate 27, no. 9 (April 23, 2014): 3208–21. http://dx.doi.org/10.1175/jcli-d-13-00611.1.
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Abstract During austral winter and spring, the El Niño–Southern Oscillation (ENSO) and the Indian Ocean dipole (IOD), individually or in combination, induce equivalent-barotropic Rossby wave trains, affecting midlatitude Australian rainfall. In autumn, ENSO is at its annual minimum, and the IOD has usually not developed. However, there is still a strong equivalent-barotropic Rossby wave train associated with tropical Indian Ocean sea surface temperature (SST) variability, with a pressure anomaly to the south of Australia. This wave train is similar in position, but opposite in sign, to the IOD-induced wave train in winter and spring and has little effect on Australian rainfall. This study shows that the SST in the southeastern tropical Indian Ocean (SETIO) displays a high variance during austral autumn, with a strong influence on southeast and eastern Australian rainfall. However, this influence is slightly weaker than that associated with SST to the north of Australia, which shares fluctuations with SST in the SETIO region. The SST north of Australia is coherent with a convective dipole in the tropical Pacific Ocean, which is the source of a wave train to the east of Australia influencing rainfall in eastern Australia. ENSO Modoki is a contributor to the convective dipole and as a result it exerts a weak influence on eastern Australian rainfall through the connecting north Australian SST relationship. Thus, SST to the north of Australia acts as the main agent for delivering the impact of tropical Indo-Pacific variability to eastern Australia.
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Chen, Yi-Ru, Bofu Yu, and Graham Jenkins. "Secular Variation in Rainfall Intensity and Temperature in Eastern Australia." Journal of Hydrometeorology 14, no. 4 (August 1, 2013): 1356–63. http://dx.doi.org/10.1175/jhm-d-12-0110.1.
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Abstract It is generally assumed that rainfall intensity will increase with temperature increase, irrespective of the underlying changes to the average rainfall. This study documents and investigates long-term trends in rainfall intensities, annual rainfall, and mean maximum and minimum temperatures using the Mann–Kendall trend test for nine sites in eastern Australia. Relationships between rainfall intensities at various durations and 1) annual rainfall and 2) the mean maximum and minimum temperatures were investigated. The results showed that the mean minimum temperature has increased significantly at eight out of the nine sites in eastern Australia. Changes in annual rainfall are likely to be associated with changes in rainfall intensity at the long duration of 48 h. Overall, changes in rainfall intensity at short durations (<1 h) positively correlate with changes in the mean maximum temperature, but there is no significant correlation with the mean minimum temperature and annual rainfall. Additionally, changes in rainfall intensity at longer durations (≥1 h) positively correlate with changes in the mean annual rainfall, but not with either mean maximum or minimum temperatures for the nine sites investigated.
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Villalobos, Yohanna, Peter J. Rayner, Jeremy D. Silver, Steven Thomas, Vanessa Haverd, Jürgen Knauer, Zoë M. Loh, Nicholas M. Deutscher, David W. T. Griffith, and David F. Pollard. "Interannual variability in the Australian carbon cycle over 2015–2019, based on assimilation of Orbiting Carbon Observatory-2 (OCO-2) satellite data." Atmospheric Chemistry and Physics 22, no. 13 (July 12, 2022): 8897–934. http://dx.doi.org/10.5194/acp-22-8897-2022.
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Abstract. In this study, we employ a regional inverse modelling approach to estimate monthly carbon fluxes over the Australian continent for 2015–2019 using the assimilation of the total column-averaged mole fractions of carbon dioxide from the Orbiting Carbon Observatory-2 (OCO-2, version 9) satellite. Subsequently, we study the carbon cycle variations and relate their fluctuations to anomalies in vegetation productivity and climate drivers. Our 5-year regional carbon flux inversion suggests that Australia was a carbon sink averaging −0.46 ± 0.08 PgC yr−1 (excluding fossil fuel emissions), largely influenced by a strong carbon uptake (−1.04 PgC yr−1) recorded in 2016. Australia's semi-arid ecosystems, such as sparsely vegetated regions (in central Australia) and savanna (in northern Australia), were the main contributors to the carbon uptake in 2016. These regions showed relatively high vegetation productivity, high rainfall, and low temperature in 2016. In contrast to the large carbon sink found in 2016, the large carbon outgassing recorded in 2019 coincides with an unprecedented rainfall deficit and higher-than-average temperatures across Australia. Comparison of the posterior column-averaged CO2 concentration with Total Carbon Column Observing Network (TCCON) stations and in situ measurements offers limited insight into the fluxes assimilated with OCO-2. However, the lack of these monitoring stations across Australia, mainly over ecosystems such as savanna and areas with sparse vegetation, impedes us from providing strong conclusions. To a certain extent, we found that the flux anomalies across Australia are consistent with the ensemble means of the OCO-2 Model Intercomparison Project (OCO-2 MIP) and FLUXCOM (2015–2018), which estimate an anomalous carbon sink for Australia in 2016 of −1.09 and −0.42 PgC yr−1 respectively. More accurate estimates of OCO-2 retrievals, with the addition of ocean glint data into our system, and a better understanding of the error in the atmospheric transport modelling will yield further insights into the difference in the magnitude of our carbon flux estimates.
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Gillett, Robert W., Ian E. Galbally, Melita D. Keywood, Jennifer C. Powell, Gavin Stevenson, Alan Yates, and Anders R. Borgen. "Atmospheric short-chain-chlorinated paraffins in Melbourne, Australia – first extensive Southern Hemisphere observations." Environmental Chemistry 14, no. 2 (2017): 106. http://dx.doi.org/10.1071/en16152.
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Environmental contextThis study presents the first comprehensive set of ambient atmospheric concentrations of short-chain-chlorinated paraffins in the Southern Hemisphere. The data show a seasonal cycle with a summer maximum and a winter minimum. The seasonal cycle is consistent with temperature dependence of the vapour pressure of the short-chain-chlorinated paraffins resulting in partitioning between the atmosphere and other reservoirs with a secondary modulation by soil moisture. AbstractThe first extensive measurements of short-chain chlorinated paraffins (SCCPs) in the atmosphere of the Southern Hemisphere are presented. The analytical and sampling methodologies used in this Australian study were verified by systematic testing along with two inter-comparisons with Northern Hemisphere laboratories with established SCCP programs. In the ambient atmosphere of Melbourne, Australia, in 2013–14, there was a clear seasonal cycle in SCCP monthly averaged concentrations, these ranging from 28.4ng m–3 in summer to 1.8ng m–3 in winter. Air temperature was the factor most closely related to the seasonal cycle in SCCPs in Melbourne. The average SCCP concentrations observed indoors were less than those observed outdoors. Atmospheric concentrations of SCCPs in Melbourne are more than two orders of magnitude higher than concentrations in the background atmosphere. Surprisingly, the SCCP concentrations in Melbourne are similar to those observed in cities in Japan, South Korea and the United Kingdom, and less than those observed in China. Direct transport of SCCPs in the atmosphere from the Northern Hemisphere emissions to Melbourne is ruled out. Instead elevated concentrations in the Melbourne air-shed are most likely a result of the long-term import of SCCPs as industrial chemicals and within manufactured materials from the Northern Hemisphere so that the use of SCCPs in Melbourne and their consequent release to the environment has produced environmental reservoirs of SCCPs in Melbourne that are comparable with those in some Northern Hemisphere cities. The increase in SCCP concentrations from winter to summer is consistent with the temperature dependence of partitioning of SCCPs between the atmosphere and other reservoirs. Insufficient information exists on SCCP use and its presence in soils and sediments in Australia to indicate whether the atmospheric presence of SCCPs in Melbourne is a legacy issue due to its import and use as a metal cutting agent in past decades or due to ongoing imports of manufactured materials containing SCCPs today.
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Kajtar, Jules B., Neil J. Holbrook, and Vanessa Hernaman. "A catalogue of marine heatwave metrics and trends for the Australian region." Journal of Southern Hemisphere Earth Systems Science 71, no. 3 (2021): 284. http://dx.doi.org/10.1071/es21014.
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Marine heatwaves around Australia, and globally, have been increasing in their frequency, intensity, and duration. This study reviews and catalogues marine heatwave metrics and trends around Australia since 1982, from near the beginning of the satellite sea-surface temperature observing period. The years in which the longest and strongest marine heatwaves around Australia occurred are also recorded. In addition, we analyse marine heatwaves in selected case study regions, and provide a short review of their associated impacts. These regions include: off the Western Australian coast, Torres Strait, Great Barrier Reef, Tasman Sea, and South Australian Basin. Finally, we provide a brief review of progress in understanding the potential predictability of sea surface temperature changes and marine heatwaves around Australia.
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Weller, Evan, Ming Feng, Harry Hendon, Jian Ma, Shang-Ping Xie, and Nick Caputi. "Interannual Variations of Wind Regimes off the Subtropical Western Australia Coast during Austral Winter and Spring." Journal of Climate 25, no. 16 (August 15, 2012): 5587–99. http://dx.doi.org/10.1175/jcli-d-11-00324.1.
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Abstract Off the Western Australia coast, interannual variations of wind regime during the austral winter and spring are significantly correlated with the Indian Ocean dipole (IOD) and the southern annular mode (SAM) variability. Atmospheric general circulation model experiments forced by an idealized IOD sea surface temperature anomaly field suggest that the IOD-generated deep atmospheric convection anomalies trigger a Rossby wave train in the upper troposphere that propagates into the southern extratropics and induces positive geopotential height anomalies over southern Australia, independent of the SAM. The positive geopotential height anomalies extended from the upper troposphere to the surface, south of the Australian continent, resulting in easterly wind anomalies off the Western Australia coast and a reduction of the high-frequency synoptic storm events that deliver the majority of southwest Australia rainfall during austral winter and spring. In the marine environment, the wind anomalies and reduction of storm events may hamper the western rock lobster recruitment process.
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Pook, M. J., J. S. Risbey, P. C. McIntosh, C. C. Ummenhofer, A. G. Marshall, and G. A. Meyers. "The Seasonal Cycle of Blocking and Associated Physical Mechanisms in the Australian Region and Relationship with Rainfall." Monthly Weather Review 141, no. 12 (November 25, 2013): 4534–53. http://dx.doi.org/10.1175/mwr-d-13-00040.1.
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Abstract The seasonal cycle of blocking in the Australian region is shown to be associated with major seasonal temperature changes over continental Antarctica (approximately 15°–35°C) and Australia (about 8°–17°C) and with minor changes over the surrounding oceans (below 5°C). These changes are superimposed on a favorable background state for blocking in the region resulting from a conjunction of physical influences. These include the geographical configuration and topography of the Australian and Antarctic continents and the positive west to east gradient of sea surface temperature in the Indo-Australian sector of the Southern Ocean. Blocking is represented by a blocking index (BI) developed by the Australian Bureau of Meteorology. The BI has a marked seasonal cycle that reflects seasonal changes in the strength of the westerly winds in the midtroposphere at selected latitudes. Significant correlations between the BI at Australian longitudes and rainfall have been demonstrated in southern and central Australia for the austral autumn, winter, and spring. Patchy positive correlations are evident in the south during summer but significant negative correlations are apparent in the central tropical north. By decomposing the rainfall into its contributions from identifiable synoptic types during the April–October growing season, it is shown that the high correlation between blocking and rainfall in southern Australia is explained by the component of rainfall associated with cutoff lows. These systems form the cyclonic components of blocking dipoles. In contrast, there is no significant correlation between the BI and rainfall from Southern Ocean fronts.
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Martin, David J. "Seasonal climate summary southern hemisphere (spring 2015): El Niño nears its peak." Journal of Southern Hemisphere Earth Systems Science 66, no. 3 (2016): 228. http://dx.doi.org/10.1071/es16017.
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Southern hemisphere circulation patterns and associated anomalies for the austral spring 2015 are reviewed, with an emphasis on Pacific climate indicators and Australian rainfall and temperature patterns. A strong El Niño persisted in the tropical Pacific Ocean with sea-surface temperature anomalies in excess of +2 °C in central and eastern parts, strongly negative outgoing longwave radiation near the Date Line, and the Southern Oscillation Index showing large negative departures. The positive Indian Ocean Dipole that had established in winter dissipated in late November, but was particularly influential on Australia's climate during the months of September and October.Australia’s spring rainfall was below average in the first two months, but improved later in the season: the northern half of Western Australia recorded above average November rainfall. Nevertheless, area-averaged rainfall in spring was below average for the country as a whole. For Australia, October was the warmest on record and had the highest mean temperature anomaly on record for any month since 1910. Spring temperatures were above average and Australia recorded its second-warmest spring on record, behind the record set in the previous year.
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Hague, Ben. "Seasonal climate summary for the southern hemisphere (summer 2016–17): a season of extremes despite neutral ENSO, IOD." Journal of Southern Hemisphere Earth Systems Science 69, no. 1 (2019): 290. http://dx.doi.org/10.1071/es19005.
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This is a summary of the southern hemisphere atmospheric circulation patterns and meteorological indices for summer 2016–17; an account of seasonal rainfall and temperature for the Australian region is also provided. Although indices for the El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) represented typical neutral condition for these drivers, evidence of other climate drivers can be found in the land, ocean and atmosphere data from this time. The Southern Annular Mode appeared to have had some effect on rainfall in the east of Australia, and the Madden–Julian Oscillation active periods produced heavy rain in the tropical north. Despite neutral ENSO and IOD, extreme temperatures, in some areas highest on record, occurred in northern NSW and southern Queensland. High sea-surface temperatures caused further severe bleaching on the Great Barrier Reef.
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Bullen, R. D., and N. L. McKenzie. "Seasonal range variation of Tadarida australis (Chiroptera:Molossidae) in Western Australia: the impact of enthalpy." Australian Journal of Zoology 53, no. 3 (2005): 145. http://dx.doi.org/10.1071/zo04080.
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The Australian bat Tadarida australis has a peculiar geographical niche that involves a continental-scale movement of over 10° of latitude in Western Australia. Its range expands northward by up to 1200 km for the winter and contracts southward for the summer. Its summer range limit correlates with an interaction of temperature and humidity, best summarised by atmospheric enthalpy. Its winter distribution is expanded northward within the enthalpy threshold, but appears to be further restricted in some areas by an unknown factor that may be biotic. We propose a potential competitor and a potential predator that may have strongly negative interactions in these regions. The 1% of records that are beyond the enthalpy envelope are from the change-over months and may be an artefact of year-to-year climatic variation. Three climatic thresholds enclose the enthalpy envelope: average annual rainfall >10 mm per month and <50 mm per month, and average overnight minimum temperature <20°C. Current literature relates migration of temperate-zone bats to resource availability as a consequence of changing season. We identify a tight correlation with atmospheric enthalpy that points to dissipation of flight muscle heat as a limiting factor.
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Ummenhofer, Caroline C., Alexander Sen Gupta, Michael J. Pook, and Matthew H. England. "Anomalous Rainfall over Southwest Western Australia Forced by Indian Ocean Sea Surface Temperatures." Journal of Climate 21, no. 19 (October 1, 2008): 5113–34. http://dx.doi.org/10.1175/2008jcli2227.1.
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Abstract The potential impact of Indian Ocean sea surface temperature (SST) anomalies in modulating midlatitude precipitation across southern and western regions of Australia is assessed in a series of atmospheric general circulation model (AGCM) simulations. Two sets of AGCM integrations forced with a seasonally evolving characteristic dipole pattern in Indian Ocean SST consistent with observed “dry year” (PDRY) and “wet year” (PWET) signatures are shown to induce precipitation changes across western regions of Australia. Over Western Australia, a significant shift occurs in the winter and annual rainfall frequency with the distribution becoming skewed toward less (more) rainfall for the PDRY (PWET) SST pattern. For southwest Western Australia (SWWA), this shift primarily is due to the large-scale stable precipitation. Convective precipitation actually increases in the PDRY case over SWWA forced by local positive SST anomalies. A mechanism for the large-scale rainfall shifts is proposed, by which the SST anomalies induce a reorganization of the large-scale atmospheric circulation across the Indian Ocean basin. Thickness (1000–500 hPa) anomalies develop in the atmosphere mirroring the sign and position of the underlying SST anomalies. This leads to a weakening (strengthening) of the meridional thickness gradient and the subtropical jet during the austral winter in PDRY (PWET). The subsequent easterly offshore (westerly onshore) anomaly in the thermal wind over southern regions of Australia, along with a decrease (increase) in baroclinicity, results in the lower (higher) levels of large-scale stable precipitation. Variations in the vertical thermal structure of the atmosphere overlying the SST anomalies favor localized increased convective activity in PDRY because of differential temperature lapse rates. In contrast, enhanced widespread ascent of moist air masses associated with frontal movement in PWET accounts for a significant increase in rainfall in that ensemble set.
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Hague, Ben S. "Seasonal climate summary for Australia and the southern hemisphere (summer 2018–19): extreme heat and flooding prominent." Journal of Southern Hemisphere Earth Systems Science 71, no. 1 (2021): 147. http://dx.doi.org/10.1071/es20009.
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This is a summary of the southern hemisphere atmospheric circulation patterns and meteorological indices for summer 2018–19; an account of seasonal rainfall and temperature for the Australian region is also provided. January 2019 was Australia’s hottest month on record, nearly 1°C warmer than any previous month. Impacts of heavy rain and floods were reported in Australia, New Zealand and South American nations. Extreme terrestrial and maritime heatwaves occurred in and around Australia and New Zealand. Case studies of the Australian heatwave, Queensland floods in January and February, and a tide-driven coastal inundation event are considered.
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Emmerson, Kathryn M., Malcolm Possell, Michael J. Aspinwall, Sebastian Pfautsch, and Mark G. Tjoelker. "Temperature response measurements from eucalypts give insight into the impact of Australian isoprene emissions on air quality in 2050." Atmospheric Chemistry and Physics 20, no. 10 (May 28, 2020): 6193–206. http://dx.doi.org/10.5194/acp-20-6193-2020.
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Abstract. Predicting future air quality in Australian cities dominated by eucalypt emissions requires an understanding of their emission potentials in a warmer climate. Here we measure the temperature response in isoprene emissions from saplings of four different Eucalyptus species grown under current and future average summertime temperature conditions. The future conditions represent a 2050 climate under Representative Concentration Pathway 8.5, with average daytime temperatures of 294.5 K. Ramping the temperature from 293 to 328 K resulted in these eucalypts emitting isoprene at temperatures 4–9 K higher than the default maximum emission temperature in the Model of Emissions of Gases and Aerosols from Nature (MEGAN). New basal emission rate measurements were obtained at the standard conditions of 303 K leaf temperature and 1000 µmol m−2 s−1 photosynthetically active radiation and converted into landscape emission factors. We applied the eucalypt temperature responses and emission factors to Australian trees within MEGAN and ran the CSIRO Chemical Transport Model for three summertime campaigns in Australia. Compared to the default model, the new temperature responses resulted in less isoprene emission in the morning and more during hot afternoons, improving the statistical fit of modelled to observed ambient isoprene. Compared to current conditions, an additional 2 ppb of isoprene is predicted in 2050, causing hourly increases up to 21 ppb of ozone and 24-hourly increases of 0.4 µg m−3 of aerosol in Sydney. A 550 ppm CO2 atmosphere in 2050 mitigates these peak Sydney ozone mixing ratios by 4 ppb. Nevertheless, these forecasted increases in ozone are up to one-fifth of the hourly Australian air quality limit, suggesting that anthropogenic NOx should be further reduced to maintain healthy air quality in future.
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Martin, David J., and Skie Tobin. "Seasonal climate summary for the southern hemisphere (winter 2017): exceptionally warm days for Australia." Journal of Southern Hemisphere Earth Systems Science 69, no. 1 (2019): 331. http://dx.doi.org/10.1071/es19012.
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This is a summary of the southern hemisphere atmospheric circulation patterns and meteorological indices for austral winter 2017; an account of seasonal rainfall and temperature for the Australian region is also provided. The El Niño–Southern Oscillation was neutral during winter 2017, as was the Indian Ocean Dipole. A positive Southern Annular Mode influenced the climates of southern hemisphere countries at times during winter. Despite the lack of large-scale ocean influences, mean temperatures for the season were very much above average across large areas of Australia, New Zealand, southern Africa and South America. Precipitation during the season was below average across much of Australia, South Africa and western areas of Chile and Argentina, but above average in some southern and eastern areas of South America.
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Taschetto, Andréa S., Alex Sen Gupta, Harry H. Hendon, Caroline C. Ummenhofer, and Matthew H. England. "The Contribution of Indian Ocean Sea Surface Temperature Anomalies on Australian Summer Rainfall during El Niño Events." Journal of Climate 24, no. 14 (July 15, 2011): 3734–47. http://dx.doi.org/10.1175/2011jcli3885.1.
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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 amplitude 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.
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Power, Scott, Malcolm Haylock, Rob Colman, and Xiangdong Wang. "The Predictability of Interdecadal Changes in ENSO Activity and ENSO Teleconnections." Journal of Climate 19, no. 19 (October 1, 2006): 4755–71. http://dx.doi.org/10.1175/jcli3868.1.
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Abstract El Niño–Southern Oscillation (ENSO) in a century-long integration of a Bureau of Meteorology Research Centre (BMRC) coupled general circulation model (CGCM) drives rainfall and temperature changes over Australia that are generally consistent with documented observational changes: dry/hot conditions occur more frequently during El Niño years and wet/mild conditions occur more frequently during La Niña years. The relationship between ENSO [as measured by Niño-4 or the Southern Oscillation index (SOI), say] and all-Australia rainfall and temperature is found to be nonlinear in the observations and in the CGCM during June–December: a large La Niña sea surface temperature (SST) anomaly is closely linked to a large Australian response (i.e., Australia usually becomes much wetter), whereas the magnitude of an El Niño SST anomaly is a poorer guide to how dry Australia will actually become. Australia tends to dry out during El Niño events, but the degree of drying is not as tightly linked to the magnitude of the El Niño SST anomaly. Nonlinear or asymmetric teleconnections are also evident in the western United States/northern Mexico. The implications of asymmetric teleconnections for prediction services are discussed. The relationship between ENSO and Australian climate in both the model and the observations is strong in some decades, but weak in others. A series of decadal-long perturbation experiments are used to show that if these interdecadal changes are predictable, then the level of predictability is low. The model’s Interdecadal Pacific Oscillation (IPO), which represents interdecadal ENSO-like SST variability, is statistically linked to interdecadal changes in ENSO’s impact on Australia during June–December when ENSO’s impact on Australia is generally greatest. A simple stochastic model that incorporates the nonlinearity above is used to show that the IPO [or the closely related Pacific Decadal Oscillation (PDO)] can appear to modulate ENSO teleconnections even if the IPO–PDO largely reflect unpredictable random changes in, for example, the relative frequency of El Niño and La Niña events in a given interdecadal period. Note, however, that predictability in ENSO-related variability on decadal time scales might be either underestimated by the CGCM, or be too small to be detected by the modest number of perturbation experiments conducted. If there is a small amount of predictability in ENSO indices on decadal time scales, and there may be, then the nonlinearity described above provides a mechanism via which ENSO teleconnections could be modulated on decadal time scales in a partially predictable fashion.
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Purich, Ariaan, Tim Cowan, Wenju Cai, Peter van Rensch, Petteri Uotila, Alexandre Pezza, Ghyslaine Boschat, and Sarah Perkins. "Atmospheric and Oceanic Conditions Associated with Southern Australian Heat Waves: A CMIP5 Analysis." Journal of Climate 27, no. 20 (October 7, 2014): 7807–29. http://dx.doi.org/10.1175/jcli-d-14-00098.1.
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Abstract Atmospheric and oceanic conditions associated with southern Australian heat waves are examined using phase 5 of the Coupled Model Intercomparison Project (CMIP5) models. Accompanying work analyzing modeled heat wave statistics for Australia finds substantial increases in the frequency, duration, and temperature of heat waves by the end of the twenty-first century. This study assesses the ability of CMIP5 models to simulate the synoptic and oceanic conditions associated with southern Australian heat waves, and examines how the classical atmospheric setup associated with heat waves is projected to change in response to mean-state warming. To achieve this, near-surface temperature, mean sea level pressure, and sea surface temperature (SST) from the historical and high-emission simulations are analyzed. CMIP5 models are found to represent the synoptic setup associated with heat waves well, despite showing greater variation in simulating SST anomalies. The models project a weakening of the pressure couplet associated with future southern Australian heat waves, suggesting that even a non-classical synoptic setup is able to generate more frequent heat waves in a warmer world. A future poleward shift and strengthening of heat wave–inducing anticyclones is confirmed using a tracking scheme applied to model projections. Model consensus implies that while anticyclones associated with the hottest future southern Australian heat waves will be more intense and originate farther poleward, a greater proportion of heat waves occur in association with a weaker synoptic setup that, when combined with warmer mean-state temperatures, gives rise to more future heat waves.
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Cai, Wenju, Peter van Rensch, Tim Cowan, and Harry H. Hendon. "Teleconnection Pathways of ENSO and the IOD and the Mechanisms for Impacts on Australian Rainfall." Journal of Climate 24, no. 15 (August 1, 2011): 3910–23. http://dx.doi.org/10.1175/2011jcli4129.1.
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Abstract Impacts of El Niño–Southern Oscillation (ENSO) and the Indian Ocean dipole (IOD) on Australian rainfall are diagnosed from the perspective of tropical and extratropical teleconnections triggered by tropical sea surface temperature (SST) variations. The tropical teleconnection is understood as the equatorially trapped, deep baroclinic response to the diabatic (convective) heating anomalies induced by the tropical SST anomalies. These diabatic heating anomalies also excite equivalent barotropic Rossby wave trains that propagate into the extratropics. The main direct tropical teleconnection during ENSO is the Southern Oscillation (SO), whose impact on Australian rainfall is argued to be mainly confined to near-tropical portions of eastern Australia. Rainfall is suppressed during El Niño because near-tropical eastern Australia directly experiences subsidence and higher surface pressure associated with the western pole of the SO. Impacts on extratropical Australian rainfall during El Niño are argued to stem primarily from the Rossby wave trains forced by convective variations in the Indian Ocean, for which the IOD is a primary source of variability. These equivalent-barotropic Rossby wave trains emanating from the Indian Ocean induce changes to the midlatitude westerlies across southern Australia, thereby affecting rainfall through changes in mean-state baroclinicity, west–east steering, and possibly orographic effects. Although the IOD does not mature until austral spring, its impact on Australian rainfall during winter is also ascribed to this mechanism. Because ENSO is largely unrelated to the IOD during austral winter, there is limited impact of ENSO on rainfall across southern latitudes of Australia in winter. A strong impact of ENSO on southern Australia rainfall in spring is ascribed to the strong covariation of ENSO and the IOD in this season. Implications of this pathway from the tropical Indian Ocean for impacts of both the IOD and ENSO on southern Australian climate are discussed with regard to the ability to make seasonal climate predictions and with regard to the role of trends in tropical SST for driving trends in Australian climate.
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Thatcher, Marcus, and John L. McGregor. "A Technique for Dynamically Downscaling Daily-Averaged GCM Datasets Using the Conformal Cubic Atmospheric Model." Monthly Weather Review 139, no. 1 (January 1, 2011): 79–95. http://dx.doi.org/10.1175/2010mwr3351.1.
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Abstract In this paper the authors dynamically downscale daily-averaged general circulation model (GCM) datasets over Australia using the Conformal Cubic Atmospheric Model (CCAM). The technique can take advantage of the wider range of Coupled Model Intercomparison Project phase 3 (CMIP3) daily-averaged GCM datasets than is available using 3-hourly datasets. The daily-averaged host GCM atmospheric data are fitted to a time interpolation formula and then differentiated in time to produce a first-order estimate of the atmosphere at 0000 UTC on each simulation day. The processed GCM data are forced into CCAM using a scale-selective filter with an 18° radius. Since this procedure is unable to account for the diurnal cycle, the forcing data are only applied to winds and air temperatures once per day between 800 and 100 hPa. Lateral boundary conditions are not required since CCAM employs a variable-resolution global grid. The technique is evaluated by downscaling daily-averaged 2.5° NCEP reanalyses over Australia at 60-km resolution from 1971 to 2000 and comparing the results to downscaling the 6-hourly reanalyses and to simulating with sea surface temperature (SST)-only forcing. The results show that the daily-averaged downscaling technique can simulate average seasonal maximum and minimum screen temperatures and rainfall similar to those obtained downscaling 6-hourly reanalyses. Some implications for regional climate projections are considered by downscaling four daily-averaged GCM datasets from the twentieth-century climate in coupled models (20C3M) experiment over Australia.
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Perkins, S. E., A. J. Pitman, N. J. Holbrook, and J. McAneney. "Evaluation of the AR4 Climate Models’ Simulated Daily Maximum Temperature, Minimum Temperature, and Precipitation over Australia Using Probability Density Functions." Journal of Climate 20, no. 17 (September 1, 2007): 4356–76. http://dx.doi.org/10.1175/jcli4253.1.
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Abstract The coupled climate models used in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change are evaluated. The evaluation is focused on 12 regions of Australia for the daily simulation of precipitation, minimum temperature, and maximum temperature. The evaluation is based on probability density functions and a simple quantitative measure of how well each climate model can capture the observed probability density functions for each variable and each region is introduced. Across all three variables, the coupled climate models perform better than expected. Precipitation is simulated reasonably by most and very well by a small number of models, although the problem with excessive drizzle is apparent in most models. Averaged over Australia, 3 of the 14 climate models capture more than 80% of the observed probability density functions for precipitation. Minimum temperature is simulated well, with 10 of the 13 climate models capturing more than 80% of the observed probability density functions. Maximum temperature is also reasonably simulated with 6 of 10 climate models capturing more than 80% of the observed probability density functions. An overall ranking of the climate models, for each of precipitation, maximum, and minimum temperatures, and averaged over these three variables, is presented. Those climate models that are skillful over Australia are identified, providing guidance on those climate models that should be used in impacts assessments where those impacts are based on precipitation or temperature. These results have no bearing on how well these models work elsewhere, but the methodology is potentially useful in assessing which of the many climate models should be used by impacts groups.
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Ma, Shaoxiu, Andy Pitman, Jiachuan Yang, Claire Carouge, Jason P. Evans, Melissa Hart, and Donna Green. "Evaluating the Effectiveness of Mitigation Options on Heat Stress for Sydney, Australia." Journal of Applied Meteorology and Climatology 57, no. 2 (February 2018): 209–20. http://dx.doi.org/10.1175/jamc-d-17-0061.1.
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AbstractGlobal warming, in combination with the urban heat island effect, is increasing the temperature in cities. These changes increase the risk of heat stress for millions of city dwellers. Given the large populations at risk, a variety of mitigation strategies have been proposed to cool cities—including strategies that aim to reduce the ambient air temperature. This paper uses common heat stress metrics to evaluate the performance of several urban heat island mitigation strategies. The authors found that cooling via reducing net radiation or increasing irrigated vegetation in parks or on green roofs did reduce ambient air temperature. However, a lower air temperature did not necessarily lead to less heat stress because both temperature and humidity are important factors in determining human thermal comfort. Specifically, cooling the surface via evaporation through the use of irrigation increased humidity—consequently, the net impact on human comfort of any cooling was negligible. This result suggests that urban cooling strategies must aim to reduce ambient air temperatures without increasing humidity, for example via the deployment of solar panels over roofs or via cool roofs utilizing high albedos, in order to combat human heat stress in the urban environment.
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Jacobs, Stephanie J., Ailie J. E. Gallant, and Nigel J. Tapper. "The Sensitivity of Urban Meteorology to Soil Moisture Boundary Conditions: A Case Study in Melbourne, Australia." Journal of Applied Meteorology and Climatology 56, no. 8 (August 2017): 2155–72. http://dx.doi.org/10.1175/jamc-d-17-0007.1.
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AbstractThe sensitivity of near-surface urban meteorological conditions to three different soil moisture initialization experiments under heat-wave conditions is investigated for the city of Melbourne, Australia. The Weather Research and Forecasting Model is used to simulate a domain over Melbourne and its surrounding rural areas. The experiments employ three suites of simulations. Two suites initialize the model with soil moisture from the top layer of the ERA-Interim soil moisture data with a 3-month and 24-h coupled spinup period, respectively. The third suite initializes the model with the arguably more realistic soil moistures from the Australian Water Availability Project (AWAP), which are an order of magnitude drier than the ERA-Interim data, again using a 24-h spinup period. The simulations employing the AWAP data are found to have smaller errors when compared with observations, with biases in urban maximum temperature reduced by 4.1°C and biases in the skin temperature reduced by 3.0°C relative to the biases of the 3-month-spinup experiment. Despite urban areas only having a small proportion of soil-covered surfaces, the results show that urban soils have a greater influence on urban near-surface temperatures at night, whereas rural soils have a greater influence on urban near-surface temperatures during the daytime.
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Magan, Bhavik, Seokhyeon Kim, Conrad Wasko, Renaud Barbero, Vincent Moron, Rory Nathan, and Ashish Sharma. "Impact of atmospheric circulation on the rainfall-temperature relationship in Australia." Environmental Research Letters 15, no. 9 (September 7, 2020): 094098. http://dx.doi.org/10.1088/1748-9326/abab35.
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Nishant, Nidhi, Giovanni Di Virgilio, Fei Ji, Eugene Tam, Kathleen Beyer, and Matthew L. Riley. "Evaluation of Present-Day CMIP6 Model Simulations of Extreme Precipitation and Temperature over the Australian Continent." Atmosphere 13, no. 9 (September 12, 2022): 1478. http://dx.doi.org/10.3390/atmos13091478.
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Australia experiences a variety of climate extremes that result in loss of life and economic and environmental damage. This paper provides a first evaluation of the performance of state-of-the-art Coupled Model Intercomparison Project Phase 6 (CMIP6) global climate models (GCMs) in simulating climate extremes over Australia. Here, we evaluate how well 37 individual CMIP6 GCMs simulate the spatiotemporal patterns of 12 climate extremes over Australia by comparing the GCMs against gridded observations (Australian Gridded Climate Dataset). This evaluation is crucial for informing, interpreting, and constructing multimodel ensemble future projections of climate extremes over Australia, climate-resilience planning, and GCM selection while conducting exercises like dynamical downscaling via GCMs. We find that temperature extremes (maximum-maximum temperature -TXx, number of summer days -SU, and number of days when maximum temperature is greater than 35 °C -Txge35) are reasonably well-simulated in comparison to precipitation extremes. However, GCMs tend to overestimate (underestimate) minimum (maximum) temperature extremes. GCMs also typically struggle to capture both extremely dry (consecutive dry days -CDD) and wet (99th percentile of precipitation -R99p) precipitation extremes, thus highlighting the underlying uncertainty of GCMs in capturing regional drought and flood conditions. Typically for both precipitation and temperature extremes, UKESM1-0-LL, FGOALS-g3, and GCMs from Met office Hadley Centre (HadGEM3-GC31-MM and HadGEM3-GC31-LL) and NOAA (GFDL-ESM4 and GFDL-CM4) consistently tend to show good performance. Our results also show that GCMs from the same modelling group and GCMs sharing key modelling components tend to have similar biases and thus are not highly independent.
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Ji, Fei, Nidhi Nishant, Jason P. Evans, Alejandro Di Di Luca, Giovanni Di Di Virgilio, Kevin K. W. Cheung, Eugene Tam, Kathleen Beyer, and Matthew L. Riley. "Rapid Warming in the Australian Alps from Observation and NARCliM Simulations." Atmosphere 13, no. 10 (October 14, 2022): 1686. http://dx.doi.org/10.3390/atmos13101686.
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The Australian Alps are the highest mountain range in Australia, which are important for biodiversity, energy generation and winter tourism. Significant increases in temperature in the past decades has had a huge impact on biodiversity and ecosystem in this region. In this study, observed temperature is used to assess how temperature changed over the Australian Alps and surrounding areas. We also use outputs from two generations of NARCliM (NSW and Australian Regional Climate Modelling) to investigate spatial and temporal variation of future changes in temperature and its extremes. The results show temperature increases faster for the Australian Alps than the surrounding areas, with clear spatial and temporal variation. The changes in temperature and its extremes are found to be strongly correlated with changes in albedo, which suggests faster warming in cool season might be dominated by decrease in albedo resulting from future changes in natural snowfall and snowpack. The warming induced reduction in future snow cover in the Australian Alps will have a significant impact on this region.
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Nguyen, Hanh, Jason A. Otkin, Matthew C. Wheeler, Pandora Hope, Blair Trewin, and Christa Pudmenzky. "Climatology and Variability of the Evaporative Stress Index and Its Suitability as a Tool to Monitor Australian Drought." Journal of Hydrometeorology 21, no. 10 (October 1, 2020): 2309–24. http://dx.doi.org/10.1175/jhm-d-20-0042.1.
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AbstractThe seasonal cycle of the evaporative stress index (ESI) over Australia, and its relationship to observed rainfall and temperature, is examined. The ESI is defined as the standardized anomaly of the ratio of actual evapotranspiration to potential evapotranspiration, and as such, is a measure of vegetation moisture stress associated with agricultural or ecological drought. The ESI is computed using the daily output of version 6 of the Bureau of Meteorology’s landscape water balance model [Australian Water Resource Assessment Landscape (AWRA-L)] on a 5-km horizontal grid over a 45-yr period (1975–2019). Here we show that the ESI exhibits marked spatial and seasonal variability and can be used to accurately monitor drought across Australia, where ESI values less than negative one indicate drought. While the ESI is highly correlated with rainfall as expected, its relationship with temperature only becomes significant during the warmer seasons, suggesting a threshold above which temperature may affect vegetation stress. Our analysis also shows that the ESI tends to be strongly negative (i.e., indicating drought) during El Niño and positive phases of the Indian Ocean dipole (IOD), when conditions tend to be anomalously hot and dry. A negative phase of the southern annular mode also tends to drive negative ESI values during austral spring with a one-month delay.
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Su, Chun-Hsu, Nathan Eizenberg, Dörte Jakob, Paul Fox-Hughes, Peter Steinle, Christopher J. White, and Charmaine Franklin. "BARRA v1.0: kilometre-scale downscaling of an Australian regional atmospheric reanalysis over four midlatitude domains." Geoscientific Model Development 14, no. 7 (July 12, 2021): 4357–78. http://dx.doi.org/10.5194/gmd-14-4357-2021.
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Abstract. Regional reanalyses provide a dynamically consistent recreation of past weather observations at scales useful for local-scale environmental applications. The development of convection-permitting models (CPMs) in numerical weather prediction has facilitated the creation of kilometre-scale (1–4 km) regional reanalysis and climate projections. The Bureau of Meteorology Atmospheric high-resolution Regional Reanalysis for Australia (BARRA) also aims to realize the benefits of these high-resolution models over Australian sub-regions for applications such as fire danger research by nesting them in BARRA's 12 km regional reanalysis (BARRA-R). Four midlatitude sub-regions are centred on Perth in Western Australia, Adelaide in South Australia, Sydney in New South Wales (NSW), and Tasmania. The resulting 29-year 1.5 km downscaled reanalyses (BARRA-C) are assessed for their added skill over BARRA-R and global reanalyses for near-surface parameters (temperature, wind, and precipitation) at observation locations and against independent 5 km gridded analyses. BARRA-C demonstrates better agreement with point observations for temperature and wind, particularly in topographically complex regions and coastal regions. BARRA-C also improves upon BARRA-R in terms of the intensity and timing of precipitation during the thunderstorm seasons in NSW and spatial patterns of sub-daily rain fields during storm events. BARRA-C reflects known issues of CPMs: overestimation of heavy rain rates and rain cells, as well as underestimation of light rain occurrence. As a hindcast-only system, BARRA-C largely inherits the domain-averaged bias pattern from BARRA-R but does produce different climatological extremes for temperature and precipitation. An added-value analysis of temperature and precipitation extremes shows that BARRA-C provides additional skill over BARRA-R when compared to gridded observations. The spatial patterns of BARRA-C warm temperature extremes and wet precipitation extremes are more highly correlated with observations. BARRA-C adds value in the representation of the spatial pattern of cold extremes over coastal regions but remains biased in terms of magnitude.
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Parker, Teresa J., Gareth J. Berry, and Michael J. Reeder. "The Structure and Evolution of Heat Waves in Southeastern Australia." Journal of Climate 27, no. 15 (July 29, 2014): 5768–85. http://dx.doi.org/10.1175/jcli-d-13-00740.1.
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Abstract The underlying large-scale dynamical processes responsible for the development of heat waves in Victoria, southeastern Australia, in summer are presented here. Heat waves are defined as periods of at least three days and two nights for which daily maximum and minimum temperatures exceed the 90th percentile for a particular location and month, using a station daily temperature dataset. Composites of upper-level potential vorticity anomalies from the Interim ECMWF Re-Analysis (ERA-Interim) reveal that heat waves in southeastern Australia are associated with propagating Rossby waves, which grow in amplitude and eventually overturn. The process of overturning generates an upper-level anticyclone over southern Australia and an upper-level trough to the northeast, with maximum amplitudes near the tropopause. The northerly flow associated with the circulation around the surface anticyclone advects hot air from the continental interior over the southeast of Australia, leading to extreme surface temperatures. Composite rainfall shows that precipitation is enhanced in the vicinity of the upper-level trough over northeastern Australia, consistent with adiabatically forced vertical motion, destabilization of the atmosphere, and modified moisture fluxes. Heat waves in the southeast are frequently accompanied by heavy rainfall over the northeast of the continent and adjacent ocean.
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Cowan, Tim, Ariaan Purich, Sarah Perkins, Alexandre Pezza, Ghyslaine Boschat, and Katherine Sadler. "More Frequent, Longer, and Hotter Heat Waves for Australia in the Twenty-First Century." Journal of Climate 27, no. 15 (July 29, 2014): 5851–71. http://dx.doi.org/10.1175/jcli-d-14-00092.1.
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Abstract Extremes such as summer heat waves and winter warm spells have a significant impact on the climate of Australia, with many regions experiencing an increase in the frequency and duration of these events since the mid-twentieth century. With the availability of Coupled Model Intercomparison Project phase 5 (CMIP5) climate models, projected changes in heat waves and warm spells are investigated across Australia for two future emission scenarios. For the historical period encompassing the late twentieth century (1950–2005) an ensemble mean of 15 models is able to broadly capture the observed spatial distribution in the frequency and duration of summer heat waves, despite overestimating these metrics along coastal regions. The models achieve a better comparison to observations in their simulation of the temperature anomaly of the hottest heat waves. By the end of the twenty-first century, the model ensemble mean projects the largest increase in summer heat wave frequency and duration to occur across northern tropical regions, while projecting an increase of ~3°C in the maximum temperature of the hottest southern Australian heat waves. Model consensus suggests that future winter warm spells will increase in frequency and duration at a greater rate than summer heat waves, and that the hottest events will become increasingly hotter for both seasons by century’s end. Even when referenced to a warming mean state, increases in the temperature of the hottest events are projected for southern Australia. Results also suggest that following a strong mitigation pathway in the future is more effective in reducing the frequency and duration of heat waves and warm spells in the southern regions compared to the northern tropical regions.
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Edwards, G. C., and D. A. Howard. "Air-surface exchange measurements of gaseous elemental mercury over naturally enriched and background terrestrial landscapes in Australia." Atmospheric Chemistry and Physics 13, no. 10 (May 27, 2013): 5325–36. http://dx.doi.org/10.5194/acp-13-5325-2013.
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Abstract. This paper presents the first gaseous elemental mercury (GEM) air-surface exchange measurements obtained over naturally enriched and background (<0.1 μg g−1 Hg) terrestrial landscapes in Australia. Two pilot field studies were carried out during the Australian autumn and winter periods at a copper-gold-cobalt-arsenic-mercury mineral field near Pulganbar, NSW. GEM fluxes using a dynamic flux chamber approach were measured, along with controlling environmental parameters over three naturally enriched and three background substrates. The enriched sites results showed net emission to the atmosphere and a strong correlation between flux and substrate Hg concentration, with average fluxes ranging from 14 ± 1 ng m−2 h−1 to 113 ± 6 ng m−2 h−1. Measurements at background sites showed both emission and deposition. The average Hg flux from all background sites showed an overall net emission of 0.36 ± 0.06 ng m−2 h−1. Fluxes show strong relationships with temperature, radiation, and substrate parameters. A compensation point of 2.48, representative of bare soils was determined. For periods of deposition, dry deposition velocities ranged from 0.00025 cm s−1 to 0.0083 cm s−1 with an average of 0.0041 ± 0.00018 cm s−1, representing bare soil, nighttime conditions. Comparison of the Australian data to North American data suggests the need for Australian-specific mercury air-surface exchange data representative of Australia's unique climatic conditions, vegetation types, land use patterns and soils.
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Emmerson, Kathryn M., Martin E. Cope, Ian E. Galbally, Sunhee Lee, and Peter F. Nelson. "Isoprene and monoterpene emissions in south-east Australia: comparison of a multi-layer canopy model with MEGAN and with atmospheric observations." Atmospheric Chemistry and Physics 18, no. 10 (May 31, 2018): 7539–56. http://dx.doi.org/10.5194/acp-18-7539-2018.
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Abstract. One of the key challenges in atmospheric chemistry is to reduce the uncertainty of biogenic volatile organic compound (BVOC) emission estimates from vegetation to the atmosphere. In Australia, eucalypt trees are a primary source of biogenic emissions, but their contribution to Australian air sheds is poorly quantified. The Model of Emissions of Gases and Aerosols from Nature (MEGAN) has performed poorly against Australian isoprene and monoterpene observations. Finding reasons for the MEGAN discrepancies and strengthening our understanding of biogenic emissions in this region is our focus. We compare MEGAN to the locally produced Australian Biogenic Canopy and Grass Emissions Model (ABCGEM), to identify the uncertainties associated with the emission estimates and the data requirements necessary to improve isoprene and monoterpene emissions estimates for the application of MEGAN in Australia. Previously unpublished, ABCGEM is applied as an online biogenic emissions inventory to model BVOCs in the air shed overlaying Sydney, Australia. The two models use the same meteorological inputs and chemical mechanism, but independent inputs of leaf area index (LAI), plant functional type (PFT) and emission factors. We find that LAI, a proxy for leaf biomass, has a small role in spatial, temporal and inter-model biogenic emission variability, particularly in urban areas for ABCGEM. After removing LAI as the source of the differences, we found large differences in the emission activity function for monoterpenes. In MEGAN monoterpenes are partially light dependent, reducing their dependence on temperature. In ABCGEM monoterpenes are not light dependent, meaning they continue to be emitted at high rates during hot summer days, and at night. When the light dependence of monoterpenes is switched off in MEGAN, night-time emissions increase by 90–100 % improving the comparison with observations, suggesting the possibility that monoterpenes emitted from Australian vegetation may not be as light dependent as vegetation globally. Targeted measurements of emissions from in situ Australian vegetation, particularly of the light dependence issue are critical to improving MEGAN for one of the world's major biogenic emitting regions.
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Potgieter, A. B., G. L. Hammer, H. Meinke, R. C. Stone, and L. Goddard. "Three Putative Types of El Niño Revealed by Spatial Variability in Impact on Australian Wheat Yield." Journal of Climate 18, no. 10 (May 15, 2005): 1566–74. http://dx.doi.org/10.1175/jcli3349.1.
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Abstract The El Niño–Southern Oscillation (ENSO) phenomenon significantly impacts rainfall and ensuing crop yields in many parts of the world. In Australia, El Niño events are often associated with severe drought conditions. However, El Niño events differ spatially and temporally in their manifestations and impacts, reducing the relevance of ENSO-based seasonal forecasts. In this analysis, three putative types of El Niño are identified among the 24 occurrences since the beginning of the twentieth century. The three types are based on coherent spatial patterns (“footprints”) found in the El Niño impact on Australian wheat yield. This bioindicator reveals aligned spatial patterns in rainfall anomalies, indicating linkage to atmospheric drivers. Analysis of the associated ocean–atmosphere dynamics identifies three types of El Niño differing in the timing of onset and location of major ocean temperature and atmospheric pressure anomalies. Potential causal mechanisms associated with these differences in anomaly patterns need to be investigated further using the increasing capabilities of general circulation models. Any improved predictability would be extremely valuable in forecasting effects of individual El Niño events on agricultural systems.
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Engel, Chermelle, and Elizabeth E. Ebert. "Gridded Operational Consensus Forecasts of 2-m Temperature over Australia." Weather and Forecasting 27, no. 2 (April 1, 2012): 301–22. http://dx.doi.org/10.1175/waf-d-11-00069.1.
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Abstract This paper describes an extension of an operational consensus forecasting (OCF) scheme from site forecasts to gridded forecasts. OCF is a multimodel consensus scheme including bias correction and weighting. Bias correction and weighting are done on a scale common to almost all multimodel inputs (1.25°), which are then downscaled using a statistical approach to an approximately 5-km-resolution grid. Local and international numerical weather prediction model inputs are found to have coarse scale biases that respond to simple bias correction, with the weighted average consensus at 1.25° outperforming all models at that scale. Statistical downscaling is found to remove the systematic representativeness error when downscaling from 1.25° to 5 km, though it cannot resolve scale differences associated with transient small-scale weather.
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Duan, Yongliang, Hongwei Liu, Weidong Yu, Lin Liu, Guang Yang, and Baochao Liu. "The Onset of the Indonesian–Australian Summer Monsoon Triggered by the First-Branch Eastward-Propagating Madden–Julian Oscillation." Journal of Climate 32, no. 17 (July 29, 2019): 5453–70. http://dx.doi.org/10.1175/jcli-d-18-0513.1.
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Abstract The Madden–Julian oscillation (MJO) often causes the onset of the Indonesian–Australian summer monsoon (IASM) over Indonesia and northern Australia. In the present study, a composite analysis is conducted to reveal the detailed IASM onset process and its air–sea interactions associated with the first-branch eastward-propagating MJO (FEMJO) based on 30-yr ERA-Interim data, satellite-derived sea surface temperature (SST), outgoing longwave radiation (OLR), and SODA3 ocean reanalysis. The results distinctly illustrate the phase-locked relationships among the persistent sea surface warming north of Australia, the FEMJO, and the established westerlies. It is found that the SST to the north of Australia reaches its annual maximum just before the onset of the summer monsoon. The oceanic surface mixed layer heat budget discloses that this rapid warming is primarily produced by the enhanced surface heat flux. In addition, this premonsoon sea surface warming increases the air specific humidity in the low-level troposphere and then establishes zonal moisture asymmetry relative to the FEMJO convection. This creates a more unstable atmospheric stratification southeast of the FEMJO and favors convection throughout the vicinity of northern Australia, which ultimately triggers the onset of the IASM. The results in this study thus may potentially be applicable to seasonal monsoon climate monitoring and prediction.
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Lee, S. Y., and T. Y. Koh. "Teleconnection between Australian winter temperature and Indian summer monsoon rainfall." Atmospheric Chemistry and Physics Discussions 11, no. 9 (September 22, 2011): 26415–40. http://dx.doi.org/10.5194/acpd-11-26415-2011.
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Abstract. The large-scale circulation over the Indian Ocean during the boreal summer raises the question of whether atmospheric conditions in Australia could influence conditions over the Indian subcontinent, despite the long passage of air over the Indian Ocean. Using a combination of reanalysis, satellite and in situ data, we argue that unusually low temperature over inland Australia during austral winter can enhance evaporation rate over the eastern tropical Indian Ocean, and hence enhance rainfall over western India after 10–18 days. Since extreme winter temperature in Australia is often associated with cold-air outbreaks, the above mechanism can be an example of how southern hemispheric mid-latitude weather can influence northern hemispheric monsoon rainfall.
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Reid, Kimberley J., Ian Simmonds, Claire L. Vincent, and Andrew D. King. "The Australian Northwest Cloudband: Climatology, Mechanisms, and Association with Precipitation." Journal of Climate 32, no. 20 (September 10, 2019): 6665–84. http://dx.doi.org/10.1175/jcli-d-19-0031.1.
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Abstract Australian northwest cloudbands (NWCBs) are continental-scale bands of continuous cloud that stretch from northwest to southeast Australia. In earlier studies, where the characteristics of NWCBs and their relationship with precipitation were identified from satellite imagery, there was considerable uncertainty in the results due to limited quality and availability of data. The present study identifies NWCBs from 31 years of satellite data using a pattern-matching algorithm. This new climatology is the longest record based entirely on observations. Our findings include a strong annual cycle in NWCB frequency, with a summer maximum and winter minimum, and a statistically significant increase in annual NWCB days over the period 1984–2014. Physical mechanisms responsible for NWCB occurrences are explored to determine whether there is a fundamental difference between summer and winter NWCBs as hypothesized in earlier studies. Composite analyses are used to reveal that a key difference between these is their genesis mechanisms. Whereas summer NWCBs are triggered by cyclonic disturbances, winter NWCBs tend to form when meridional sea surface temperature gradients trigger baroclinic instability. It was also found that while precipitation is enhanced over parts of Australia during a cloudband day, it is reduced in other regions. During a cloudband day, precipitation extremes are more likely over northwest, central, and southeast Australia, while the probability of extreme precipitation decreases in northeast and southwest Australia. Additionally, cold fronts and NWCBs can interact, leading to enhanced rainfall over Australia.
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Weller, Evan, and Wenju Cai. "Asymmetry in the IOD and ENSO Teleconnection in a CMIP5 Model Ensemble and Its Relevance to Regional Rainfall." Journal of Climate 26, no. 14 (July 12, 2013): 5139–49. http://dx.doi.org/10.1175/jcli-d-12-00789.1.
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Abstract Recent studies have shown that the impact of the Indian Ocean dipole (IOD) on southern Australia occurs via equivalent barotropic Rossby wave trains triggered by convective heating in the tropical Indian Ocean. Furthermore, the El Niño–Southern Oscillation (ENSO) influence on southern Australian climate is exerted through the same pathway during austral spring. It is also noted that positive phase [positive IOD (pIOD) and El Niño] events have a much larger impact associated with their respective skewness. These phenomena play a significant role in the region's rainfall reduction in recent decades, and it is essential that climate models used for future projections simulate these features. Here, the authors demonstrate that climate models do indeed simulate a greater climatic impact on Australia for pIOD events than for negative IOD (nIOD) events, but this asymmetric impact is distorted by an exaggerated influence of La Niña emanating from the Pacific. The distortion results from biases in the Pacific in two respects. First, the tropical and extratropical response to La Niña is situated unrealistically too far westward and hence too close to Australia, leading to an overly strong impact on southeast Australia that shows up through the nIOD–La Niña coherence. Second, the majority of models simulate a positive sea surface temperature skewness in the eastern Pacific that is too weak, overestimating the impact of La Niña relative to that of El Niño. As such, the impact of the positive asymmetry in the IOD only becomes apparent when the impact of ENSO is removed. This model bias needs to be taken into account when analyzing projections of regional Australian climate change.
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Ayers, Gregory P. "Australia's Air Temperature Trend Reviewed." Journal of Southern Hemisphere Earth Systems Science 66, no. 3 (2016): 270. http://dx.doi.org/10.1071/es16019.
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The hypothesis of an artificially exaggerated temperature trend in the Australian continental surface air temperature record is tested via comparison with four other records of temperature measured in the Australian region. The trends extracted from all five records are consistent, so the hypothesis of bias in the Bureau of Meteorology’s Australian surface air temperature record cannot be sustained and is rejected. Using three different methods of trend estimation applied to five temperature anomaly time series, the anthropogenic contribution to warming of the Australian region since 1950 is determined to have occurred at a rate of 0.12 ± 0.02K per decade, which translates to a total anthropogenic warming contribution of 0.78 ± 0.13K over the period 1950 to 2015.
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Hirsch, Annette L., Jatin Kala, Andy J. Pitman, Claire Carouge, Jason P. Evans, Vanessa Haverd, and David Mocko. "Impact of Land Surface Initialization Approach on Subseasonal Forecast Skill: A Regional Analysis in the Southern Hemisphere." Journal of Hydrometeorology 15, no. 1 (February 1, 2014): 300–319. http://dx.doi.org/10.1175/jhm-d-13-05.1.
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Abstract The authors use a sophisticated coupled land–atmosphere modeling system for a Southern Hemisphere subdomain centered over southeastern Australia to evaluate differences in simulation skill from two different land surface initialization approaches. The first approach uses equilibrated land surface states obtained from offline simulations of the land surface model, and the second uses land surface states obtained from reanalyses. The authors find that land surface initialization using prior offline simulations contribute to relative gains in subseasonal forecast skill. In particular, relative gains in forecast skill for temperature of 10%–20% within the first 30 days of the forecast can be attributed to the land surface initialization method using offline states. For precipitation there is no distinct preference for the land surface initialization method, with limited gains in forecast skill irrespective of the lead time. The authors evaluated the asymmetry between maximum and minimum temperatures and found that maximum temperatures had the largest gains in relative forecast skill, exceeding 20% in some regions. These results were statistically significant at the 98% confidence level at up to 60 days into the forecast period. For minimum temperature, using reanalyses to initialize the land surface contributed to relative gains in forecast skill, reaching 40% in parts of the domain that were statistically significant at the 98% confidence level. The contrasting impact of the land surface initialization method between maximum and minimum temperature was associated with different soil moisture coupling mechanisms. Therefore, land surface initialization from prior offline simulations does improve predictability for temperature, particularly maximum temperature, but with less obvious improvements for precipitation and minimum temperature over southeastern Australia.
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Taschetto, Andréa S., and Matthew H. England. "El Niño Modoki Impacts on Australian Rainfall." Journal of Climate 22, no. 11 (June 1, 2009): 3167–74. http://dx.doi.org/10.1175/2008jcli2589.1.
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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.
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Liess, Stefan, Arjun Kumar, Peter K. Snyder, Jaya Kawale, Karsten Steinhaeuser, Frederick H. M. Semazzi, Auroop R. Ganguly, Nagiza F. Samatova, and Vipin Kumar. "Different Modes of Variability over the Tasman Sea: Implications for Regional Climate*." Journal of Climate 27, no. 22 (November 4, 2014): 8466–86. http://dx.doi.org/10.1175/jcli-d-13-00713.1.
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Abstract A new approach is used to detect atmospheric teleconnections without being bound by orthogonality (such as empirical orthogonal functions). This method employs negative correlations in a global dataset to detect potential teleconnections. One teleconnection occurs between the Tasman Sea and the Southern Ocean. It is related to El Niño–Southern Oscillation (ENSO), the Indian Ocean dipole (IOD), and the southern annular mode (SAM). This teleconnection is significantly correlated with SAM during austral summer, fall, and winter, with IOD during spring, and with ENSO in summer. It can thus be described as a hybrid between these modes. Given previously found relationships between IOD and ENSO, and IOD’s proximity to the teleconnection centers, correlations to IOD are generally stronger than to ENSO. Increasing pressure over the Tasman Sea leads to higher (lower) surface temperature over eastern Australia (the southwestern Pacific) in all seasons and is related to reduced surface temperature over Wilkes Land and Adélie Land in Antarctica during fall and winter. Precipitation responses are generally negative over New Zealand. For one standard deviation of the teleconnection index, precipitation anomalies are positive over Australia in fall, negative over southern Australia in winter and spring, and negative over eastern Australia in summer. When doubling the threshold, the size of the anomalous high-pressure center increases and annual precipitation anomalies are negative over southeastern Australia and northern New Zealand. Eliassen–Palm fluxes quantify the seasonal dependence of SAM, ENSO, and IOD influences. Analysis of the dynamical interactions between these teleconnection patterns can improve prediction of seasonal temperature and precipitation patterns in Australia and New Zealand.
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Potemra, James T., and Niklas Schneider. "Influence of Low-Frequency Indonesian Throughflow Transport on Temperatures in the Indian Ocean in a Coupled Model*." Journal of Climate 20, no. 7 (April 1, 2007): 1339–52. http://dx.doi.org/10.1175/jcli4146.1.
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Abstract The relationship between 3- and 10-yr variability in Indian Ocean temperatures and Indonesian throughflow (ITF) volume transport is examined using results from a 300-yr integration of the coupled NCAR Parallel Climate Model (PCM). Correlation and regression analyses are used with physical reasoning to estimate the relative contributions of changes in ITF volume transport and Indian Ocean surface atmospheric forcing in determining low-frequency temperature variations in the Indian Ocean. In the PCM, low-frequency variations in ITF transport are small, 2 Sv (1 Sv ≡ 106 m3 s−1), and have a minimal impact on sea surface temperatures (SSTs). Most of the low-frequency variance in Indian Ocean temperature (rms > 0.5°C) occurs in the upper thermocline (75–100 m). These variations largely reflect concurrent atmospheric forcing; ITF-induced temperature variability at this depth is limited to the outflow region between Java and Australia extending westward along a band between 10° and 15°S.
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Wang, Guomin, and Harry H. Hendon. "Sensitivity of Australian Rainfall to Inter–El Niño Variations." Journal of Climate 20, no. 16 (August 15, 2007): 4211–26. http://dx.doi.org/10.1175/jcli4228.1.
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Abstract Australia typically experiences drought during El Niño, especially across the eastern two-thirds of the continent during austral spring (September–November). There have, however, been some interesting departures from this paradigm. For instance, the near-record-strength El Niño of 1997 was associated with near-normal rainfall. In contrast, eastern Australia experienced near-record drought during the modest El Niño of 2002. This stark contrast raises the issue of how the magnitude of the drought is related to the character and magnitude of El Niño, for instance as measured by the broadscale sea surface temperature (SST) anomaly in the equatorial eastern Pacific. Internal (unpredictable) atmospheric noise is one plausible explanation for this contrasting behavior during these El Niño events. Here, the authors suggest that Australian rainfall is sensitive to the zonal distribution of SST anomalies during El Niño and, in particular, the greatest sensitivity is to the SST variations on the eastern edge of the Pacific warm pool rather than in the eastern Pacific where El Niño variations are typically largest. Positive SST anomalies maximized near the date line in 2002, but in 1997 maximum anomalies were shifted well into the eastern Pacific, where their influence on Australian rainfall appears to be less. These findings provide a plausible physical basis for the view that forecasting the strength of El Niño is not sufficient to accurately predict rainfall variations across Australia during El Niño.