School of Earth Sciences - Research Publications
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ItemNo Preview AvailableRevised stratigraphy of the Blanchetown Clay, Murray Basin: age constraints on the evolution of paleo Lake Bungunnia(TAYLOR & FRANCIS LTD, 2009)
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ItemNo Preview AvailableDistribution of Palaeozoic reworking in the Western Arunta Region and northwestern Amadeus Basin from 40Ar/39Ar thermochronology: implications for the evolution of intracratonic basins(WILEY, 2009-06)ABSTRACT The Centralian Superbasin in central Australia is one of the most extensive intracratonic basins known from a stable continental setting, but the factors controlling its formation and subsequent structural dismemberment continue to be debated. Argon thermochronology of K‐feldspar, sensitive to a broad range of temperatures (∼150 to 350 °C), provides evidence for the former extent and thickness of the superbasin and points toward thickening of the superbasin succession over the now exhumed Arunta Region basement. These data suggest that before Palaeozoic tectonism, there was around 5–6 km of sediment present over what is now the northern margin of the Amadeus Basin, and, if the Centralian superbasin was continuous, between 6 and 8 km over the now exhumed basement.40Ar/39Ar data from neoformed fine‐grained muscovite suggests that Palaeozoic deformation and new mineral growth occurred during the earliest compressional phase of the Alice Springs Orogeny (ASO) (440–375 Ma) and was restricted to shear zones. Significantly, several shear zones active during the late Mesoproterozoic Teapot Orogeny were not reactivated at this time, suggesting that the presence of pre‐existing structures was not the only controlling factor in localizing Palaeozoic deformation. A range of Palaeozoic ages of 440–300 Ma from samples within and external to shear zones points to thermal disturbance from at least the early Silurian through until the late Carboniferous and suggests final cooling and exhumation of the terrane in this interval. The absence of evidence for active deformation and/or new mineral growth in the late stages of the ASO (350–300 Ma) is consistent with a change in orogenic dynamics from thick‐skinned regionally extensive deformation to a more restricted localized high‐geothermal gradient event.
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ItemNo Preview AvailableAge constraints on Oligocene sedimentation in the Torquay Basin, southeastern Australia(TAYLOR & FRANCIS LTD, 2009)
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ItemPrecipitation Simulations Using WRF as a Nested Regional Climate Model(AMER METEOROLOGICAL SOC, 2009-10)Abstract This note examines the sensitivity of simulated U.S. warm-season precipitation in the Weather Research and Forecasting model (WRF), used as a nested regional climate model, to variations in model setup. Numerous options have been tested and a few of the more interesting and unexpected sensitivities are documented here. Specifically, the impacts of changes in convective and land surface parameterizations, nest feedbacks, sea surface temperature, and WRF version on mean precipitation are evaluated in 4-month-long simulations. Running the model over an entire season has brought to light some issues that are not otherwise apparent in shorter, weather forecast–type simulations, emphasizing the need for careful scrutiny of output from any model simulation. After substantial testing, a reasonable model setup was found that produced a definite improvement in the climatological characteristics of precipitation over that from the National Centers for Environmental Prediction–National Center for Atmospheric Research global reanalysis, the dataset used for WRF initial and boundary conditions in this analysis.
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ItemDecadal prediction: can it be skilful?(American Meteorological Society, 2009)A new field of study, “decadal prediction,” is emerging in climate science. Decadal prediction lies between seasonal/interannual forecasting and longer-term climate change projections, and focuses on time-evolving regional climate conditions over the next 10–30 yr. Numerous assessments of climate information user needs have identified this time scale as being important to infrastructure planners, water resource managers, and many others. It is central to the information portfolio required to adapt effectively to and through climatic changes. At least three factors influence time-evolving regional climate at the decadal time scale: 1) climate change commitment (further warming as the coupled climate system comes into adjustment with increases of greenhouse gases that have already occurred), 2) external forcing, particularly from future increases of greenhouse gases and recovery of the ozone hole, and 3) internally generated variability. Some decadal prediction skill has been demonstrated to arise from the first two of these factors, and there is evidence that initialized coupled climate models can capture mechanisms of internally generated decadal climate variations, thus increasing predictive skill globally and particularly regionally. Several methods have been proposed for initializing global coupled climate models for decadal predictions, all of which involve global time-evolving three-dimensional ocean data, including temperature and salinity. An experimental framework to address decadal predictability/prediction is described in this paper and has been incorporated into the coordinated Coupled Model Intercomparison Model, phase 5 (CMIP5) experiments, some of which will be assessed for the IPCC Fifth Assessment Report (AR5). These experiments will likely guide work in this emerging field over the next 5 yr.
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ItemAtypical influence of the 2007 La Nina on rainfall and temperature in southeastern Australia(American Geophysical Union, 2009)Interannual climate variations associated with El Niño – Southern Oscillation (ENSO) dominate rainfall and temperature variability in southeastern Australia's Murray-Darling Basin (MDB), an important region for agricultural productivity. Following a decade-long dry period, a La Niña during 2007 failed to provide above average rainfall and cool temperatures in the southern half of the MDB, typical of most La Niña events for the region. Instead, annual (winter half-year) rainfall was 17% (35%) below average and maximum temperatures 0.91°C (1.26°C) above average. Based on the past variability between La Niña events, the combined probability of such anomalies is less than 2%. It is likely that these anomalies contain some contribution from a positive Indian Ocean Dipole (IOD). However, the IOD and other large-scale circulation features are unlikely to explain the atypical conditions that occurred in the southern MDB during the 2007 La Niña.
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ItemA climate reconstruction of Sydney Cove, New South Wales, using weather journal and documentary data, 1788-1791(Australian Meteorological and Oceanographic Society, 2009)This study presents the first analysis of the weather conditions experienced at Sydney Cove, New South Wales, during the earliest period of the European settlement of Australia. A climate analysis is presented for January 1788 to December 1791 using daily temperature and barometric pressure observations recorded by William Dawes in Sydney Cove and a temperature record kept by William Bradley on board the HMS Sirius anchored in Port Jackson (Sydney Harbour) in the early months of the First Fleet’s arrival in Australia. Remarkably, the records appear comparable with modern day measurements taken from Sydney Observatory Hill, displaying similar daily variability, a distinct seasonal cycle and considerable inter-annual variability. To assess the reliability of these early weather data, they were cross-verified with other data sources, including anecdotal observations recorded in First Fleet documentary records and independent palaeoclimate reconstructions. Some biases in the temperature record, likely associated with the location of the thermometer, have been identified. Although the 1788–1791 period experienced a marked La Niña to El Niño fluctuation according to palaeoclimatic data, the cool and warm intervals in Sydney over this period cannot be conclusively linked to El Niño– Southern Oscillation (ENSO) conditions. This study demonstrates that there are excellent opportunities to expand our description of pre-20th century climate variability in Australia while contributing culturally significant material to the emerging field of Australian environmental history.
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ItemObservation and modeling of stable water isotopes as diagnostics of rainfall dynamics over southeastern Australia(AMER GEOPHYSICAL UNION, 2009-12-09)A unified approach of observation and modeling was applied to the investigation of three circulation types that typically bring rain to southeastern Australia. Observations from the Melbourne University Network of Isotopes in Precipitation of high‐resolution variations in the ratios of 18O and 2H were collected for (1) mixed frontal, (2) convective, and (3) stratiform precipitation events. Isotopic content of precipitation varied over both high and low frequencies because of influences from local variations in rain intensity and rainout by large‐scale precipitation. Deuterium excess showed a weak relationship with rainfall amount on intraevent time scales but was stronger under convective rainfall conditions. As a supplement to the observations, a version of the National Center for Atmospheric Research Community Atmosphere Model running an isotope hydrology scheme simulated the mixed frontal and stratiform events by nudging with reanalyses. The simulations represented well the evolution of vapor profiles of 18O and deuterium excess. Trajectories for the mixed frontal case illustrated the structure of the vapor profiles, revealing a convergence of air masses from different source regions. Deuterium excess in precipitation was represented less accurately by the model, indicating a possible shortcoming in the parameterization of postcondensation processes in the general circulation model. By combining observations and modeling in this way, detail of the structure and history of the events was provided that would be unavailable from the sampling of precipitation alone.
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ItemBiases in the calculation of Southern Hemisphere mean baroclinic eddy growth rate(American Geophysical Union, 2009)The maximum Eady growth rate measure of baroclinic instability is very commonly used in the literature. Its average is usually calculated directly from the time-mean flow. It is suggested here that this approach is not entirely suitable, but rather one should obtain the Eady growth rates at all relevant synoptic times and average these. It is found at the 850 hPa level in the Southern Hemisphere that the time-mean of the instantaneous rates exceed those calculated from the time-mean field over much of the mid and high latitudes, and the difference is even more marked at 500 hPa. At both levels the axes of the maxima Eady growth rates are displaced to the south. Some implications are discussed, including the need for caution when diagnosing changes in cyclone properties from changes in Eady growth rate calculated directly from the time-mean flow in climate change model simulations.
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ItemNew perspectives on the synoptic development of the severe October 1992 Nome storm(AMER GEOPHYSICAL UNION, 2009-07-14)Understanding the characteristics of storms that impact the Alaska region is of importance to emergency planning. The 5–7 October 1992 storm was a severe event which cost Nome, a town in Alaska, $6 million dollars. We will explore its characteristics with the aid of two established cyclone tracking schemes: the NOAA CPC current operational algorithm and the University of Melbourne algorithm. Manual tracking was performed as a control. The essential features are captured by both algorithms, but they differ in the genesis and lysis location. The NOAA algorithm broke the storm into two separate events. Synoptic development of the storm was influenced by a blocking high that affected how the tracking algorithms handled the event. A synoptic re‐examination of this storm is presented in terms of the depth, Laplacian and radius of the system. These new results present a fresh perspective on the intensity and longevity of this dramatic storm.