School of Earth Sciences - Research Publications
Permanent URI for this collection
Search Results
1 - 4 of 4
-
ItemLong-term stationarity of El Nino-Southern Oscillation teleconnections in southeastern Australia(Springer (part of Springer Nature), 2016-05-01)The El Niño–Southern Oscillation (ENSO) phenomenon plays a large role in the modulation of Aaustralian rainfall, particularly in the highly populated southeast. However, this influence is not stationary over time: weak ENSO teleconnections in Australia have been identified during 1920–1950, and palaeoclimate reconstructions indicate that a breakdown in global ENSO teleconnections may have also occurred in the early to mid-1800s. A lack of long-term instrumental data has prevented detailed examination of this intriguing earlier period. This study uses newly recovered instrumental rainfall observations to determine whether the weakening of ENSO teleconnections in the nineteenth century is apparent in eastern and southern southeastern Australia (SEA). Quantitative rainfall and rainday data from 1788 to 2012 are compared with three ENSO indices derived from palaeoclimate data. Statistical analysis suggests a weakening of the relationship between ENSO and SEA rainfall in the early nineteenth century data (~1835–1850), supporting results reported in previous global and regional studies based on palaeoclimate and documentary rainfall reconstructions. Possible causes of this weakening in teleconnection strength are then explored by examining a range of Southern Hemisphere circulation indices. The 1835–1850 period of low ENSO–SEA rainfall correlations appears to be characterised by a combination of reduced La Niña events and ENSO variance associated with a positive phase of the Interdecadal Pacific Oscillation, with the possible influence of a predominately negative phase of the Southern Annular Mode. However, current temporal and geographical data limitations prevent definitive conclusions from being drawn. Despite these caveats, this study illustrates the considerable value of historical instrumental climate data in assessing long-term variations in climate mode teleconnections, particularly in the data-poor Southern Hemisphere.
-
ItemNo Preview AvailableAustralasian Temperature Reconstructions Spanning the Last Millennium(AMER METEOROLOGICAL SOC, 2016-08)Abstract Multiproxy warm season (September–February) temperature reconstructions are presented for the combined land–ocean region of Australasia (0°–50°S, 110°E–180°) covering 1000–2001. Using between 2 (R2) and 28 (R28) paleoclimate records, four 1000-member ensemble reconstructions of regional temperature are developed using four statistical methods: principal component regression (PCR), composite plus scale (CPS), Bayesian hierarchical models (LNA), and pairwise comparison (PaiCo). The reconstructions are then compared with a three-member ensemble of GISS-E2-R climate model simulations and independent paleoclimate records. Decadal fluctuations in Australasian temperatures are remarkably similar between the four reconstruction methods. There are, however, differences in the amplitude of temperature variations between the different statistical methods and proxy networks. When the R28 network is used, the warmest 30-yr periods occur after 1950 in 77% of ensemble members over all methods. However, reconstructions based on only the longest records (R2 and R3 networks) indicate that single 30- and 10-yr periods of similar or slightly higher temperatures than in the late twentieth century may have occurred during the first half of the millennium. Regardless, the most recent instrumental temperatures (1985–2014) are above the 90th percentile of all 12 reconstruction ensembles (four reconstruction methods based on three proxy networks—R28, R3, and R2). The reconstructed twentieth-century warming cannot be explained by natural variability alone using GISS-E2-R. In this climate model, anthropogenic forcing is required to produce the rate and magnitude of post-1950 warming observed in the Australasian region. These paleoclimate results are consistent with other studies that attribute the post-1950 warming in Australian temperature records to increases in atmospheric greenhouse gas concentrations.
-
ItemNo Preview AvailableA historical climate dataset for southeastern Australia, 1788-1859(WILEY, 2014-11)There is a significant lack of historical climate data in the Southern Hemisphere compared to the northern latitudes. To address this data scarcity and to improve understanding of regional climate variability, historical instrumental observations were recovered for southeastern Australian (SEA) for the 1788–1859 period. Instrumental observations of temperature, atmospheric pressure, rainfall and raindays were rescued from 39 archival sources, and examined to identify observer biases and inhomogeneities. The rescued data provide continuous information on SEA climate variability from 1826 to 1859, with short periods of observations identified between 1788–1791, 1803–1805 and 1821–1824. Quality control and homogenization of each data source indicates that the historical observations successfully capture regional interannual climate variability. The historical records exhibit high correlations between neighbouring observations and related climate variables. The instrumental observations also display very good agreement with documentary climate reconstructions, further verifying their quality. As an example of how this new historical dataset may be used, regional averages of the observations were calculated to estimate interannual climate variability across SEA from 1826 to 1859. Prolonged dry conditions were identified in various parts of the region during 1837–1843 and 1845–1852, while wet conditions were noted from 1836 to 1838, primarily in southern SEA. Anomalously cold periods were also identified in 1835–1836 and 1848–1849, in general agreement with temperature reconstructions from other regions of the Southern Hemisphere. This new dataset provides a valuable source of subdaily to monthly information on SEA climate variability for future climate analysis, palaeoclimate reconstruction verification and historical studies.
-
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.