ORCID Profile
0000-0002-9631-8181
Current Organisation
Australian Bureau of Meteorology
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Publisher: Wiley
Date: 02-07-2021
Publisher: CSIRO Publishing
Date: 16-03-2021
DOI: 10.1071/ES20003
Abstract: Climate scientists routinely rely on averaging over time or space to simplify complex information and to concisely communicate findings. Currently, no consistent definitions of ‘warm’ or ‘cool’ seasons for southern Australia exist, making comparisons across studies difficult. Similarly, numerous climate studies in Australia use either arbitrarily defined areas or the Natural Resource Management (NRM) clusters to perform spatial averaging. While the NRM regions were informed by temperature and rainfall information, they remain somewhat arbitrary. Here we use weather type influence on rainfall and clustering methods to quantitatively define climatic regions and seasons over southern Australia. Three methods are explored: k-means clustering and two agglomerative clustering methods, Ward linkage and average linkage. K-means was found to be preferred in temporal clustering, while the average linkage method was preferred for spatial clustering. For southern Australia as a whole, we define the cool season as April–September and warm season as October–March, though we note that a three-season split may provide more nuanced climate analysis. We also show that different regions across southern Australia experience different seasons and demonstrate the changing spatial influence of weather types with the seasons, which may aid regionally or seasonally specific climate analysis. Division of southern Australia into 15 climatic regions shows localised agreement with the NRM clusters where distinct differences in rainfall amounts exist. However, the climate regions defined here better represent the importance of topographical aspect on weather type influence and the inland extent of particular weather types. We suggest that the use of these regions would provide consistent climate analysis across studies if widely adopted. A key requirement for climate scientists is the simplification of data sets into both seasonally or regionally averaged subsets. This simplification, by grouping like regions or seasons, is done for a number of reasons both scientific and practical, including to help understand patterns of variability, underlying drivers and trends in climate and weather, to communicate large amounts of data concisely, to reduce the amount of data required for processing (which becomes increasingly important with higher resolution climate model output), or to more simply draw a physical boundary between regions for other purposes, such as flora and fauna habitat analysis, appropriate agricultural practices or water management.
Publisher: Wiley
Date: 13-10-2021
Publisher: Wiley
Date: 03-12-2021
Publisher: Springer Science and Business Media LLC
Date: 03-08-2022
DOI: 10.1007/S00382-021-05903-9
Abstract: We examine the climatology, variability and change in the global mean meridional circulation (MMC) as measured in a dry isentropic coordinate system from 1979–2017 using the ERA-Interim reanalysis. The methodology presents a zonal-mean view of the MMC as a single thermally direct circulation cell in each hemisphere. The circulation is decomposed into 'steady' and 'transient' components which allows us to identify and quantify several MMC features, including the Intertropical Convergence Zone, the descending branches of the Hadley circulation and a 'transient updraft' associated with the extratropical storm track. Large changes were identified in the Southern Hemisphere (SH) in both the Hadley Cell and the extratropical storm track in the late-1990s. These changes intertwine with the Interdecadal Pacific Oscillation that changed from a warm to a cold phase around 2000. Less significant changes were observed in the Northern Hemisphere, although high rates of tropical expansion during boreal summer may have been exacerbated by volcanic eruptions in the 1980s and 1990s. Further to those changes, tropical expansion was observed in autumn, with little change in the extratropical storm track. While potential inhomogeneities in the reanalysis limit the certainty about the magnitude of the identified changes, multiple non-reanalysis-based datasets suggest that large changes did occur in the 1990s in the SH, supporting the presented analysis.
Publisher: American Geophysical Union (AGU)
Date: 29-12-2022
DOI: 10.1029/2021JD035433
Abstract: The factors driving variability in rainfall stable water isotopes (specifically δ 18 O and deuterium excess, d = δ 2 H − 8 δ 18 O) were studied in a 13‐year data set of daily rainfall s les from coastal southwestern Western Australia (SWWA). Backwards dispersion modeling, automatic synoptic type classification, and a statistical model were used to establish causes of variability on a daily scale and predictions from the model were aggregated to longer temporal scales to discover the cause of variability on multiple timescales. Factors differ between δ 18 O and d and differ according to temporal scale. Rainfall intensity, both at the observation site and upwind, was most important for determining δ 18 O and this relationship was robust across all time scales (daily, seasonal, and interannual) as well as generalizing to a second observation site. The sensitivity of δ 18 O to rainfall intensity makes annual mean values particularly sensitive to the year's largest events. Projecting the rainfall intensity relationship back through ∼100 years of precipitation observations can explain ∼ –0.4‰ shifts in rainfall δ 18 O. Twentieth century speleothem records from the region exhibit signals of a similar magnitude, indicating that rainfall intensity should be taken into account during the interpretation of regional climate archives. For d , humidity during evaporation from the ocean was the most important driver of variability at the daily scale, as well as explaining the seasonal cycle, but source humidity failed to explain the longer‐term interannual variability.
Publisher: Elsevier BV
Date: 07-2023
Publisher: Springer Science and Business Media LLC
Date: 26-10-2017
Publisher: Wiley
Date: 20-01-2023
DOI: 10.1002/WCC.820
Abstract: Southern Australia's rainfall is highly variable and influenced by factors across scales from synoptic weather to large‐scale circulation and remote climate modes of variability. Anthropogenic climate change and natural variability modulate these factors and their interactions. However, studies often focus on changes in selected parts of the climate system with less emphasis on the system as a whole. As such, it is difficult to gain a complete understanding of how southern Australia's rainfall responds to broad‐scale changes in the climate system. We step through the existing literature on long‐term changes in synoptic‐to‐large‐scale atmospheric circulation and drivers of climate variability to form a more complete story of rainfall changes across southern Australia. This process reveals that the most robust change is the observed winter decline in rainfall as it is consistent with several changing climatic factors: decreasing rainfall from weather systems, strengthening subtropical ridge, poleward shifts in the Hadley Cell and the Southern Annular Mode, and increasing frequency of positive Indian Ocean Dipole events. In other seasons, particularly summer, changes in atmospheric circulation and drivers may not agree with observed rainfall changes, highlighting gaps in our knowledge of atmospheric dynamics and climate change processes. Future work should focus on research across temporal‐ and spatial‐scales, better understanding of jet interactions, the influence of stratospheric processes on the troposphere, and instances of contrasting trends in drivers and southern Australian rainfall changes. This article is categorized under: Paleoclimates and Current Trends Modern Climate Change Paleoclimates and Current Trends Detection and Attribution Assessing Impacts of Climate Change Observed Impacts of Climate Change
Publisher: Informa UK Limited
Date: 02-01-2020
Publisher: Springer Science and Business Media LLC
Date: 22-01-2021
Publisher: American Geophysical Union (AGU)
Date: 23-09-2018
DOI: 10.1029/2018GL079312
Abstract: During the summer months, there is a semipermanent trough in the low‐level easterlies over the west coast of Australia. This “West Coast Trough” plays an important role in summer severe weather in western Australia including thunderstorms and severe heat waves. The land‐sea contrast is believed to be the driver of the location of this trough. As land masses are warming more quickly than their surrounding oceans, it is timely to readdress the drivers of the location and intensity of this important climatological feature. Using a 20‐year regional climate modeling simulation, we show that Australian orography is critical to the accurate representation of the trough in climate models, in contrast to earlier low‐resolution studies.
Publisher: American Geophysical Union (AGU)
Date: 06-2023
DOI: 10.1029/2022WR033692
Abstract: Many Victorian catchments experienced a rainfall‐runoff relationship (RRR) shift during the Millennium Drought (1997–2009). Less annual streamflow was generated from annual rainfall during the drought than would have been expected for the same rainfall before the drought. Changes in weather systems, such as cyclones, fronts, and thunderstorms, were also observed during this period. In this study, we assess the role that changes in weather systems played in the RRR shift. We find that catchments that experienced a RRR shift tended to receive less of their rainfall from frontal weather systems, and more of their rainfall from thunderstorm‐enhanced cyclone and cyclone‐front hybrid systems during the drought than catchments that showed little change in RRR. Overall, changes in the proportion of rainfall from weather systems alone explained up to 43% of the variance in the RRR shift between catchments. Including parameters that quantify catchment processes and physiographic features indicated that weather system changes are not the primary indicator of a RRR shift. Catchment mean slope, aridity and valley confinement, together with proportional rainfall change of cyclone‐thunderstorms and cyclone‐front‐thunderstorms, explained 60% of the variance in the RRR shift between catchments. Focusing on streamflow availability, we find the importance of different weather systems and catchment characteristics varies depending on warm or cool season, eastern or western Victoria, and before or during the drought. Following the drought, some catchments largely maintained the RRR shift that occurred during the drought, and also experienced less of their rainfall from fronts and cyclones compared to the other catchments.
Publisher: Elsevier BV
Date: 03-2021
No related grants have been discovered for Pandora Hope.