School of Earth Sciences - Research Publications

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Author: Ashcroft, Linden × Author: Gergis, Joelle × Author: Karoly, David × Start date: 2000 ×

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    Long-term stationarity of El Nino-Southern Oscillation teleconnections in southeastern Australia
    Ashcroft, L ; Gergis, J ; Karoly, DJ (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.
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    A historical climate dataset for southeastern Australia, 1788-1859
    Ashcroft, L ; Gergis, J ; Karoly, DJ (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.