School of Earth Sciences - Theses

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Sea level forecasts, tide prediction and mesoscale operational oceanography in Australia

Taylor, Andrew J ( 2021)

This thesis addresses conceptual issues at the intersection of sea level forecasting, tides and mesoscale oceanography with implications for operational practice. New methods for combining, evaluating and delivering nominally “tidal” sea level information are proposed and analysed, with a focus on representation issues and system compatibility. The results are expected to inform the development of seamless forecasting services and assert that aspects of conventional tide prediction will maintain relevance by supporting increasingly sophisticated numerical and data-driven prognostic tools. The study motivation and scope originates from within the ongoing operational movement towards what are increasingly called seamless services. All of the data and systems treated in this study reflect the setting within the Australian Bureau of Meteorology, though the findings are not specifically restricted in relevance to Australia. Chapter 1 portrays the operational context and establishes the relevance of the study scope being restricted to the overlap of mesoscale forecasts and tide prediction; chapter 2 unpacks relevant technical details and concepts within the seamless framework to highlight problematic areas of overlap or incompatibility; chapter 3 responds to this situation of overlap to present a methodology for deriving improved forecast value from existing systems to both set a performance benchmark for candidate ocean forecast system updates and elucidate details of predictability relevant to operational services; chapter 4 also addresses the topic of updates and extensions to the operational ocean forecasting suites by presenting an approach to connect the academic literature treating coastally trapped waves with the operational evaluation of candidate systems and guidance provided to forecasting staff; chapter 5 returns to the role of conventional tide prediction within the evolving operational suite of forecasting systems and proposes incremental but significant changes to the nature of that service to mitigate issues related to conceptual overlap and allow for ongoing ; finally chapter 6 considers the results of the study in the context of wider trends towards seamless forecasting and discusses how the peculiar characteristics of sea level demonstrate that forecast service plans should include more than the canonical pattern of nested simulations. The primary findings of the thesis are summarised as follows: Firstly, it was demonstrated that incompatible definitions of ocean “tide” are in parallel operational use. Whereas downscaling for coastal sea level forecasts is clearly a productive approach, mesoscale ocean forecasts can immediately and directly provide significant but qualified forecast value for coastal sea level. The fact that nominally tidal signals are present in mesoscale non-tidal ocean simulations means that care is required to avoid misinterpretation. An aggregation approach that combines existing heterogeneous data but accounts for double-counting provides an important skill benchmark for future sea level forecast system development. The point-based bias correction characteristics from these aggregated forecasts indicate that coastally contiguous extensions to model aggregation may be feasible. In the operational context of combining and upgrading forecast models, it was shown that the coastal propagation characteristics of candidate forecast systems can be usefully evaluated and compared in a grid-independent waveguide projection. Such a coastal waveguide projection also offers a means to direct forecaster attention to signals of special relevance along the Australian mainland coast. Finally, it was argued that conventional harmonic tide predictions are not redundant, despite the ongoing advances in hydrodynamic simulation, but that operational tide services require appropriate product differentiation to compliment modern applications and facilitate future refinement.
Antarctic sea ice and its interactions with high latitude weather and climate

Watkins, Andrew Bruce ( 1998)

Antarctic sea ice plays a major role in the earth system by greatly influencing the high latitude exchanges of heat, moisture and momentum between the ocean and atmosphere, as well as profoundly effecting the salt budget of the ocean, and thus the production of Antarctic Bottom Water, one of the driving mechanisms of worldwide oceanic circulation. With such considerable and far reaching impact, it is important to document its climatology, understand its variability and quantify its influence. Climatologies and trends of the Southern Ocean sea ice pack are presented using the most recent satellite observations available from the Defense Meteorological Program’s (DMSP) Special Sensor Microwave Imager (SSM/I). The analysis of these data show that Antarctic sea ice is highly variable in both time and space. Statistically significant increases in the sea ice extent, open water and ice areas have been determined from the SSM/I data for the 9 year period 1987 to 1996, a result which differs from the Scanning Multichannel Microwave Radiometer (SMMR) observations (1978-1987). The increasing trend in the SSM/I observations can be attributed to the large increases in sea ice observed in 1994-1995, as confirmed by an analysis of data from the ERS-1 satellite. The mean season length during these years has remained relatively unchanged. Regional trends, both in the sea ice concentration and in season length, showed vast spatial inhomogeneity. SSM/I data displayed increasing season length in the central Weddell Sea, Bellingshausen Sea and Balleny Islands regions, with decreasing length in the Amundsen Sea, eastern Ross Sea and in the coastal areas off Wilkes Land. Similar trends are observed in the seasonal sea ice concentration. In most cases, these trends are opposite to those observed in the SMMR data, which may be linked to the shift observed in the Amundsen Sea low after 1990. Comparisons with historical data would suggest that no large scale anomalous change has occurred in the Antarctic sea ice limits over the course of human observation. Furthermore, the degree of variability suggests great care is needed in interpreting large scale changes in sea ice conditions, and hence atmospheric or oceanic change, from locally observed anomalies. Case studies of the effect of individual cyclones upon the sea ice concentration show small but definite modification of the ice conditions. To further diagnose aspects of the thermodynamic and dynamic forcing upon the Antarctic pack, detailed analysis of the sea ice concentration variability has been conducted using spectral techniques, and the spectra have been compared to those of the European Centre for Medium Range Weather Forecasts (ECMWF) temperature and wind data. In all cases, and with the seasonal cycle removed, the sea ice concentration shows a bias towards longer timescales of variability than either the wind stress or surface air temperature. This “red shift” in its frequency spectrum is strongest with the wind stress, and weakest with the temperature. For longer period waves, this may be due to the formation of new ice by surface cooling or the moderation of melting by the cold surface water, whereas for shorter period waves, where wind stress dominates temperature and ice concentration respectively, time is required for winds to draw in warmer or cooler air, as well as to overcome the ice masses inertia and keel friction to open or close leads. Strong intraseasonal variability of the sea ice concentration is observed in the 20-25 day period, reflecting similar timescales of the temperature variability, as well as that of the energetic eddies of the Antarctic circumpolar current. Examination of the latitudinal variation of the sea ice concentration, temperature and wind stress spectra showed not only the importance of the north-south temperature gradient in influencing the variability, but also the seasonal changes in the semi annual oscillation of the circumpolar trough. Regional spectra showed clear differences between location, and reflected the influences of the atmosphere and ocean upon the sea ice pack. This is clearly shown in the Weddell Polynya region and off East Antarctica, with high variability in the synoptic timescales, and in the western Ross Sea where changes occur in timescales of greater than 20 days. In order to determine if satellite derived, real time sea ice concentration and distribution would be of benefit to operational numerical weather prediction (NWP) schemes, the effect of sea ice concentration change upon the atmosphere in synoptic timescales was examined using a general circulation model in conjunction with the Australian Bureau of Meteorology’s GASP analyses. Experiments were conducted with a typical July sea ice concentration and distribution, as well as slab concentrations of 0, 10, 25, 50, 80 and 100%. Results from 5-day numerical weather forecasts show that the central pressure, structure and tracks of individual cyclones are sensitive to the ‘switch on’ of different sea ice conditions. Composites of all forecasts made with each concentration showed considerable, and mostly statistically significant, anomalies in the surface temperatures and turbulent heat fluxes over the sea ice. The magnitudes of these changes varied monotonically with the area of open water. The largest changes were simulated closest to the coast for all concentrations except for the typical July sea ice run, which displayed maxima over the outer pack. Significant westerly anomalies were induced over the ice in all cases, as were reductions in mean sea level pressure. The July sea ice runs displayed a distribution of the mean sea level pressure anomaly different from all others, with maxima occurring in the central to outer pack. All other forecasts displayed maxima at the coast. The results suggest that sea ice concentration does induce anomalies in the atmospheric parameters in timescales of less than five days. Further, the use of a realistic distribution of sea ice concentration produces results distinct from the constant concentration forecasts. Hence it is suggested that real time Antarctic sea ice data may be of considerable benefit to numerical weather prediction models.
Australian rainfall and El Niño diversity: past variability and context for recent changes

Freund, Mandy Barbara ( 2018)

The climate system integrates internally and externally induced variability at various time scales as a result of interactions between the ocean and atmosphere. The influence of external forcing on the climate system and with it the structural changes of climate variability, in particular on seasonal and longer time-scales, is difficult to examine due to high natural variability and short observational records. The interplay between high and low-frequency variability restricts our understanding of the full range of climate variability and our ability to contextualise changes. This thesis explores and evaluates the potential to use seasonal paleoclimate information to advance our knowledge of natural climate variability and the multi-century context of recent changes in the Australasian and tropical Pacific region. Climate modes of variability including the El Niño -Southern Oscillation influence Australian rainfall and make Australian rainfall highly variable at interannual timescales. Multi-century reconstructions of past climate variability are developed for Australian rainfall at bi-seasonal resolution. The rainfall reconstruction is based on local paleoclimate proxies and teleconnected links between remote paleoclimate proxies, climate modes of variability and Australian rainfall. In a multi-century context, the recent drying trends in parts of southern Australia, as well as the tendency towards wetter conditions in northern Australia, are found to be unusual. The cool and warm season rainfall reconstructions allow the documentation of distinct characteristics of past major droughts in terms of their spatial extent, duration, intensity, and seasonality. Using coral data at seasonal resolution, two El Niño index reconstructions illustrate the sequence of diversity of past eastern and central Pacific El Niño events for the last 400 years. The distinct spatio-temporal signatures of both types of El Niño are exploited, and together with a novel machine learning approach, the diversity of past El Niño events is reconstructed and compared to recent changes. The recent increase in the frequency of central Pacific El Niño events relative to eastern Pacific El Niño events during the late 20th century appears unusual. The most recent 30-year period includes more intense eastern Pacific events compared to the past four centuries. To further investigate the changes and interactions between Australian rainfall and El Niño diversity, observations and climate model simulations are compared to the multi-century reconstructions. A number of climate models taking part in the Coupled Model Intercomparison Project Phase 5 (CMIP5) are identified that simulate spatially distinct El Niño behaviour. Identification of El Niño events reveals a lack of model agreement about projected changes of El Niño diversity. The probability of infrequent El Niño characteristics is evaluated and point towards an under-representation of central Pacific events that are followed by eastern Pacific events in the observational records. Future simulations in climate models indicate that this El Niño transition as observed most recently in 2014-2016, could become less common. Based on the rainfall and El Niño reconstructions, the general drying impacts of El Niño is consistent for both types. Despite the strength asymmetry between eastern and central Pacific El Niño events, the impact on Australian rainfall is of a similar order of magnitude but also highlights a strong variable nature of the different types of El Niño and Australian hydroclimate. The context of recent changes provided by the reconstructions in this thesis advances our knowledge of natural climate variability in the Australasian and tropical Pacific region and offers new insights into the future climate of the region.
Fire weather in two regions of the Southern Hemisphere

Pazmiño, Daniel ( 2017)

This thesis investigated fire weather in Victoria, Australia and the Ecuadorian Andes. The selection of these areas considered several criteria. First of all, bushfires cause significant impacts in these two regions. Victoria has endured some of the most catastrophic bushfire events in Australian history (e.g. “Black Friday” (1939), “Ash Wednesday” (1983), “Black Saturday” (2009)). On the other hand, bushfires in Ecuador destroy every year large areas of national parks in one of the most biodiverse countries in the world. Secondly, the El Niño- Southern Oscillation (ENSO) is a strong climate driver in the two study areas. Finally, Victoria and Ecuador share the Eucalyptus as the dominant bushfire-prone species. The aim of this thesis is to better understand the drivers and evolution of fire weather in these two regions of the Southern Hemisphere. Specifically, it examined three aspects. First of all, it investigated fire weather spatial patterns in Victoria and their relationship with associated events like heatwaves. Subsequently, the study explored long-term fire weather variability and changes. Finally, the investigation evaluated the influence of ENSO and other climate drivers over fire weather. The analyses used three groups of data: bushfire records, meteorological and climate indices data. Consistent bushfire records were available only for Victoria during the period 1961-2010. Additionally, the investigation required observations from weather stations in Victoria and the Ecuadorian Andes. This research also analysed reanalysis data from the Twentieth Century Reanalysis Project (20CR) and the European Reanalysis of Global Climate Observations ERA-Clim project (ERA-20C). The study had a stronger emphasis on ENSO since it affects both regions. This research used two indices to represent fire weather. The first index was the McArthur Forest Fire Danger Index (FFDI). This Australian metric was designed for an Eucalyptus environment. Therefore, this investigation applied the FFDI for Victoria and Ecuador. Additionally, this thesis proposes an alternative fire weather index for Victoria: the “Victorian Seasonal Bushfire Index” (VSBI). The VSBI combines local meteorological variables and sea surface temperature in ENSO regions to represent—and predict—extreme fire weather. The investigation of fire weather in Victoria and the Ecuadorian Andes yielded several findings. First of all, bushfire and heatwave weather patterns display differences from one another in Victoria. These comparisons used synoptic climatologies with reanalysis data during the period 1961-2010. Additionally, the investigation showed that Victoria experienced an increase in fire danger during the period 1974-2010. There is also weaker evidence suggesting an increasing trend since 1920. “El Niño” events are the leading remote driver of fire activity in Victoria. In fact, the incorporation of ENSO indicators in a simple index (VSBI) shows skill to forecast extreme fire weather in this region. For the Ecuadorian Andes, this research indicates that its fire danger season (July-September) is longer than reported. October and November also display “high” fire danger during the period 1997-2012. Finally, “El Niño” events increase fire risk in the Ecuadorian Andes.
Measurement and modelling of heat flow in the Gippsland Basin, Victoria

HARRISON, BENJAMIN ( 2015)

Geothermal energy has the potential to provide significant quantities of highly available power with little environmental impact. Enhanced geothermal system (EGS) technologies have the potential to become major contributors to global energy production, with a much wider geographic scope than the more established conventional geothermal systems. Certain favourable geological conditions have been recognised as providing improved prospectivity for EGS resources, primarily elevated heat flow rates and thermally insulating cover sequences. Most attention has been given to the location of regions having anomalously high heat flow, typically due to increased heat production in basement rocks such as granites rich in radiogenic isotopes. Little attention has been paid to extremes in thermal insulation, which offer an alternative but equally effective mechanism for increasing geothermal gradients and thus reducing the depth to a geothermal resource. Large and thick deposits of highly insulating coal present a unique thermal environment, where the commonly assumed one-dimensional relationship between surface heat flow and temperature at depth described by Fourier's Law is not maintained due to heat refraction -- a three-dimensional process. Understanding the effects of heat refraction due to thermal insulation and its effect on surface heat flow is a crucial element of exploration strategies in coal-bearing sedimentary basins. The onshore Gippsland Basin, and in particular the Latrobe Valley, is an ideal setting to study the effects of buried confined insulators on surface heat flow and thermal structure. This thesis combines the results of observational insights from empirical field data collection with mathematically driven insights of theoretical models, and simulation-driven insights of numerical finite-element modelling. Additionally, it explores the relatively modern paradigm of data-driven statistical science to generate predictions of rock properties from related intrinsic variables. Measured surface heat flow is moderately variable, with the ten most reliable calculations from borehole data having an interquartile range of 61--78 mW/m², with a mean and standard deviation of 72±14 mW/m², slightly higher than previous estimates. Groundwater advection identified in previous studies appears to affect the thermal structure of only the Cainozoic stratigraphy. Losses of up to 37 mW/m² in the vertical heat flow in the sandy Balook Formation of borehole Rosedale-301 represents a local maximum of heat transfer associated with groundwater advection. Only minor thermal effects are observed in the uppermost Mesozoic section, indicating a return to a dominantly conductive thermal regime there. The self-organising map technique was applied to the prediction of lithostratigraphy and thermal conductivity from well-log data. It successfully identified 91.3% of lithostratigraphy samples from a supervised mapping of well-log data. Mapping of thermal conductivity with corresponding well-log data produced more variable results compared with a petrophysical log interpretation technique over a large cohort of boreholes. However, the SOM analysis returned predicted values with a better correlation with measured values at sampled depths, required less pre-processing of log data, and was able to perform with non-standard log data and legacy tools. With further refinements of the technique, potential improvements may be made with its prediction performance of thermal conductivity and other rock properties. Heat flow theory applied to an idealised simulation of the Latrobe Valley coal seams showed that temperature increases of 35°C beneath the coal are possible over a reference model having no such insulation. Finite-element forward models of cross-sections and 3D volumes through the onshore Gippsland Basin identified highly variable surface heat flow, having up to ±30 mW/m² variance from the basal flux input. Complex patterns resulting from heat refraction were produced, with two common features indicative of confined insulators: 1. the greatest increase in subsurface temperature is correlated with the greatest decrease in surface heat flow, however, 2. surface heat flow tends to be slightly increased above the margins of buried insulators. The main implication from these results is the identification of an end-member insulation-dominated geothermal resource style, requiring new strategies for exploration and resource targeting.
Investigating the diurnal variation of the water and energy cycle

RAUNIYAR, SURENDRA ( 2015)

Many weather forecasting models have fundamental difficulties in accurately predicting the intensity and timing of rainfall over the Maritime Continent (MC) just north of Australia, a region known as the weather “boiler box” of the globe. Here, we examine the spatio-temporal variability of the diurnal cycle of rainfall over the MC and northern Australia caused by the major modes of climate variability, namely the Madden Julian Oscillation (MJO) and the El Niño Southern Oscillation (ENSO) using the high resolution TRMM 3B42 and 3G68 rainfall datasets. In addition, using datasets of unprecedented spatial and temporal resolutions over Darwin, Australia and its vicinity, a life-cycle of rainfall building mechanisms is examined during an event of the eastward progressing MJO to determine the reasons behind occurrence of secondary maximum rainfall in the diurnal cycle of rainfall at Darwin. Distinct variations in the rainfall distribution pattern amongst categories of the MJO over land and ocean are seen. The result of the composite mean rainfall distribution shows that the average daily rainfall rate over many parts of islands is substantially higher compared to the climatology during the suppressed MJO. In contrast, over the surrounding oceans and northern regions of Australia more rainfall occurs during MJO active days. These differences are also well depicted in large-scale dynamical and thermodynamical fields derived from the NCEP reanalyses. Unlike previous studies, we found that the MJO modulates both the amplitude and phase of the diurnal cycle of rainfall. The amplitude of morning maximum rainfall near coastal areas during active days of the MJO is 1.5 times greater than the climatological mean rainfall, but is less than or equal to the climatological mean during other phases of the MJO and depends on the local geography and orography. Similarly, the peak in the diurnal cycle for active and suppressed/weak days of the MJO respectively, lags and leads the peak in the diurnal cycle for total rainfall by two hours. Despite the alternating patterns of widespread large-scale subsidence and ascent associated with the Walker circulation, which dominates the climate over the MC during the opposing phases of ENSO, many of the islands of the MC show localized differences in rainfall anomalies that depend on the local geography and orography. While ocean regions mostly experience positive rainfall anomalies during La Niña, some local regions over the islands have more rainfall during El Niño. These local features are also associated with anomalies in the amplitude and characteristics of the diurnal cycle in these regions. These differences are also well depicted in large-scale dynamical fields derived from the ERA-interim reanalyses. Detailed analysis of rainfall building mechanisms over Darwin and its vicinity showed that the large-scale forcing dominates during the MJO phase 4 - 7, starting by the reversal of low- to mid-level easterly winds to moist westerly winds, reaching a maximum in phase 5 and weakening through phases 6 to 7. During phases 4-6, most of the study domain experiences widespread rainfall, but with distinct spatial and temporal structures. In addition, during these phases, coastal areas near Darwin receive more rainfall in the early morning due to the spreading or expansion of rainfall from the Beagle Gulf, explaining the occurrence of a secondary peak over Darwin. Even with correct initialization of the MJO, the 12 km resolution ACCESS-A model fails to simulate this peak. In contrast, local-scale mechanisms (sea breezes) reinvigorate from phase 8, further strengthening through phases 1-3, when low-level easterly winds become established over Darwin producing rainfall predominately over land and island locations during the afternoon. During these phases, below average rainfall is observed over most of the radar domain, except over the Tiwi Islands in phase 2.
Exploring the palaeoclimate potential of South East Australian speleothems

Green, Helen Elizabeth ( 2013)

The paucity of palaeoclimatic data existing for the Southern Hemisphere and the regional bias of new data from the Northern Hemisphere has meant conclusions regarding the global response to the numerous climatic events of the last 20 kyr is both widely disputed and poorly understood. Despite being one of the Southern Hemisphere’s largest landmasses, Australia in particular displays a limited pool of palaeoclimatic information and the production of a new, robust record providing an insight into the response and timing of key climatic events is paramount to generating a more comprehensive characterisation and improved understanding of palaeoclimate in this region. Speleothems (cave deposits) are valuable archives of palaeoclimate variation, characterised by their extensive growth intervals and large geographic extent. They contain a multitude of ‘proxy’ records both directly and indirectly linked to climatic fluctuations and are typically robust, displaying high preservation potential with no post-depositional alteration. Key to their success is their amenability to radiometric dating, allowing the establishment of robust and reliable chronologies to which their multi-proxy records can be anchored. Consequently speleothems provide a clear opportunity to explore and expand palaeoclimatic knowledge at sites across the globe. This thesis describes and explains the use of state of the art technology to exploit relatively recent advances in U-series dating to construct reliable and detailed records of south east Australia’s response to palaeoclimatic fluctuations over the last 50 kyr using samples collected from cave sites from across the states of Victoria and New South Wales. 28 speleothem samples have been analysed in terms of both their coincident growth intervals and stable isotope variation to provide records with palaeoclimatic implications at a range of time scales. The production of a chronological template of speleothem growth intervals has enabled the assessment of south east Australia’s response to some of the key local and global millennial scale climatic events of the last glacial to interglacial transition and detailed stable isotope analysis of selected samples have been interpreted with the aid of a thorough cave monitoring programme, identifying increased variability in the region’s climate during the late Holocene. The palaeoclimatic records developed in this thesis represent a significant step forward in Southern Hemispheric palaeoclimatology. These records offer valuable new data for both palaeoclimatologists exploring south east Australia’s past climate and those investigating climatic fluctuations at a hemispheric to global scale. The high resolution and robust chronology of the records produced means that they provide a benchmark to which future records might be anchored.
The weather and climate of Australia at the Last Glacial Maximum

Hope, Pandora ( 2005)

The global climate has experienced four glacial cycles in the last 420,000 years, with each cycle characterised by a prolonged period of cooling culminating in maximal glaciation followed by a brief warm period. The most recent period of maximal glaciation is termed the Last Glacial Maximum (LGM) and occurred about 21,000 years ago. We currently live in one of the warm periods. The global climate is changing, and it is becoming more important to understand the extremes of the climate system and how well our modelling capability can capture those extremes. There has been a modelling intercomparison project established to examine how global general circulation models compare in simulating past climates, including the LGM. Analysis and comparison of these model results has been presented for many parts of the globe, but there has not been a comparison of the different model results over the Australian region. This thesis aims to fill that gap and explore the simulated LGM weather and climate of Australia and its drivers in more detail. Comparison with proxy evidence is also undertaken, and inconsistencies seen in the literature addressed. The Australian climate at the LGM was believed to be generally cooler, drier and possibly windier from proxy evidence in the literature. In the comparison done here the mean temperature and precipitation fields from most models show cooler and drier conditions, with some seasonal variability, but there are some strong outliers. It was found that the differences were not dependent on model resolution, but that the surface parameterisations were highly important for these fields. The shifts in the circulation were examined both in the model results and with a study of the non-linear link between the wind, surface moisture and dunes, which are a proxy for past winds. All the models simulate a southward shift in the westerlies in the Australian region. This is strongly driven byte prescribed sea-surface temperatures. Australia's current wind regime is conducive to dune building. However, the binding effect of soil moisture (or vegetation) is strong enough to limit present day movement, whereas in the drier climate at the LGM there was a capacity for sand movement. The analysis of dune orientations did not produce conclusive evidence for how the westerlies might have shifted at the LGM. An apparent enigma in the proxy evidence at the LGM is the high lake levels in Australia’s south east, while most inland lakes were dry. Previous authors believed that the precipitation was still low, but the high lake levels were driven by lowered potential evaporation. The hydrological cycle was generally depressed in the LGM simulations, but the potential for evaporation remained high. Thus an alternative hypothesis is posed based on increased run off due to a known shift in the vegetation types and a lag in the timing of the run off due to snowmelt. The analysis here shows that our capacity to simulate climates quite different from the present is still developing, but that model results can help explain apparent inconsistencies in the reconstruction of past climates from proxies.
The development of a high quality historical temperature data base for Australia

Torok, Simon James ( 1996)

A high quality, historical surface air temperature data set is essential for the reliable investigation of climate change and variability. In this study, such a data set has been prepared for Australia by adjusting raw mean annual temperature data for inhomogeneities associated with station relocations, changes in exposure, and other problems. Temperature records from long-term stations were collaborated from the set of all raw data held by the Australian Bureau of Meteorology. These long-term records were extended by combining stations and manually entering previously unused archived temperature measurements. An objective procedure was developed to determine the necessary adjustments, in conjunction with complementary statistical methods and station history documentation. The objective procedure involved creating a reference time series for each long-term station, from the median values at surrounding, well-correlated stations. Time series of annual mean maximum and mean minimum temperatures have been produced for 224 stations, and the adjusted dataset has been made available to the research community. The adjusted data are likely to be more representative of real climatic variations than raw data due to the removal of discontinuities. The adjusted data set has been compared with previously used temperature data sets, and data sets of other parameters. The adjusted data set provides adequate spatial coverage of Australia back to 1910. Additional adjusted data are available prior to this date at many stations. Trends in annual mean maximum, minimum, the mean of the maximum and minimum, and the range between the maximum and minimum, have been calculated at each site. Maximum and minimum temperatures have increased since about 1950, with minimum temperatures increasing faster than maximum temperatures.
Vertical structure Of atmospheric trace gases over Southeast Australia

Pak, Bernard Ching-Yuen ( 2000-01)

Trace gas (CO2 and its carbon and oxygen isotopes, CH4, CO, H2 and N2O) vertical profile data above Cape Grim, Tasmania for the period April 1992 to February 1997 are investigated. A climatology of the distribution of each trace gas has been compiled from statistical treatment of the raw data. These climatologies are useful for verification of transport model outputs. Here, the CO2 climatology is compared to simulation results from two transport models (Melbourne University Transport Model and TM2Z) using three different sets of CO2 fluxes separately (compiled with different methods by different authors). Large discrepancies are found between simulations and observations, especially in the free troposphere (4-6 km). By considering emission ratios, trajectories, satellite fire counts and simulation with biomass burning fluxes, the influence of tropical biomass burning plumes on the southeastern Australian region in the austral winter/spring is studied and quantified. This identification process requires a multiple-species approach where the large CO anomalies and the unexpected behaviour of H2 are most revealing. The frequent presence of burning plumes in the mid troposphere complicates one of the original motivations for the Cape Grim Overflight Program, which is to estimate the air-sea exchange of CO2 in this region. A suggestion arising from analysis of pre-1992 aircraft sampling in this region was that the regional CO2 air-sea flux south of Australia is exceptionally large.

School of Earth Sciences - Theses

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