The influences on Australian east coast lows in present and future climates

East Coast Lows (ECLs) are midlatitude cyclones that develop on the east coast of Australia, responsible for the majority of coastal flooding, large waves, erosion, and dam-filling events. Because of their impacts, there is a need to better understand both how and why they develop, and how they may change in coming decades. The objective of this thesis was to use a combination of observational datasets and regional climate model simulations to improve our understanding of the influences on the frequency, characteristics, and impacts of East Coast Lows in both the present and future climates. Key outcomes include: - Assessing the representation of ECLs in reanalysis data, and identifying that the observed interannual variability and seasonal distribution of East Coast Lows are sensitive to the identification method used. - Evaluating the skill of high-resolution regional climate models to reproduce the observed frequency and distribution of ECLs - Developing the most robust projections of future ECL activity in the coming century, using an ensemble of regionally-downscaled climate model projections for Australia and a number of automated methods for identifying ECLs. This identified a robust decline in future ECLs during the winter months, but large uncertainty in the warm season and for ECLs close to the coast. The frequency of ECLs associated with heavy rain is likely to increase in both seasons. - Quantifying the impact of the East Australian Current and Great Dividing Range on the frequency, intensity, and impacts of ECLs using a suite of multi-year regional climate model experiments. Warmer oceans were identified as important for the development of weak to moderate ECLs, with a 20% increase in ECL frequency for a 1 2°C increase in coastal sea surface temperatures, with a lesser influence on the most intense events. Changes to topography had a smaller impact on the frequency and distribution of ECLs, with a 7 10% decline in ECLs when topography was removed. However, the detailed effects of topography on ECL characteristics were sensitive to the modelling approach used. In total, this thesis represents a substantial improvement of our understanding of East Coast Lows in regional climate model simulations

Multi-decadal increase of forest burned area in Australia is linked to climate change

Fire activity in Australia is strongly affected by high inter-annual climate variability and extremes. Through changes in the climate, anthropogenic climate change has the potential to alter fire dynamics. Here we compile satellite (19 and 32 years) and ground-based (90 years) burned area datasets, climate and weather observations, and simulated fuel loads for Australian forests. Burned area in Australia’s forests shows a linear positive annual trend but an exponential increase during autumn and winter. The mean number of years since the last fire has decreased consecutively in each of the past four decades, while the frequency of forest megafire years (>1 Mha burned) has markedly increased since 2000. The increase in forest burned area is consistent with increasingly more dangerous fire weather conditions, increased risk factors associated with pyroconvection, including fire-generated thunderstorms, and increased ignitions from dry lightning, all associated to varying degrees with anthropogenic climate change

Subseasonal to Seasonal Climate Forecasts Provide the Backbone of a Near-Real-Time Event Explainer Service

The Bureau of Meteorology serves the Australian community to reduce its climate risk and is developing a suite of tools to explain the drivers of extreme events. Dynamical sub-seasonal to seasonal forecasts form the backbone of the service, potentially enabling it to be run in near real time

Dynamics and predictability of El Nino-Southern Oscillation: an Australian perspective on progress and challenges

Many scientific challenges remain for managing the risk of future ENSO impacts in countries like Australia that are strongly affected by ENSO event diversity

Global cyclone and anticyclone tracks, 1948-2022

This dataset includes all global surface anticyclones as well as both surface and 500hPa cyclones tracked using the University of Melbourne cyclone tracking scheme over all available years until 2022. The dataset is an update of that available at https://doi.org/10.6084/m9.figshare.c.4944135.v1, but with some changes to parameters:The intensity of surface cyclones is based on the Laplacian averaged within 2 degrees of the centre rather than 5 degrees, to better detect the most intense part of the low500hPa lows are also included. In contrast to previous datasets for ERA5 (e.g. https://doi.org/10.6084/m9.figshare.19669518.v1) these are tracked using 6-hourly instantaneous 500hPa geopotential height, rather than daily mean fields.These anticyclones and cyclones were identified using the Murray and Simmonds (1991) and Simmonds et al. (1999) cyclone tracking scheme. The source code and documentation is available at https://cyclonetracker.earthsci.unimelb.edu.au/, with additional example processing scripts available at https://github.com/apepler/cyclonetracking. The included ".incycloc" and ".intrack" files give the parameters used for tracking. Tracks are provided for ERA5 during 1959-2022, JRA55 for 1958-2022, and NCEP1 for 1948-2022. Cyclone tracks are provided based on the weakest intensity threshold, noting that the associated paper reports results for only lows exceeding additional minimum intensity thresholds. Both open and closed circulations are included, although only closed circulations are used in the paper. Each zipfile contains all results for a single synoptic type and reanalysis. A separate track file is provided for each year, beginning on 1 December of the previous year, to allow for the identification of cross-year tracks when relevant.Column headings:ID Track IDFix Instance within trackDate Date* (UTC)Time Time (UTC)Open/closed Is there closed circulation (0) or an "open" ridge. Lon LongitudeLat LatitudeMSLP Central pressure (hPa) or central height (Z500, m)Laplacian Laplacian of MSLP (hPa. Deg.lat^2) or (m. Deg.lat^2), which represents the curvature of the MSLP. This is a better indicator of the strength of a system, and represents the curvature of the field. Depth Depth of system relative to the background region (hPa)Radius Radius of system (degrees)Up Steering velocity (U)Vp Steering velocity (V)*Dates are two digit years, and in some cases are wrong because of the way the tracking scheme works (e.g. 1999-2001) These need to be corrected when using multiple files, noting that the true year of the Jan-Dec data is given in the filename.References:Murray, R. J., and I. Simmonds, 1991: A numerical scheme for tracking cyclone centres from digital data. Part I: Development and operation of the scheme. Aust. Meteorol. Mag., 39, 155166.Simmonds, I., R. J. Murray, and R. M. Leighton, 1999: A refinement of cyclone tracking methods with data from FROST. Aust. Meteorol. Mag., (special edition), 3549.Pepler (2023) Emerging trends in extratropical lows and their rainfall over Australia (submitted to ERCL)</ul

A robust error-based rain estimation method for polarimetric radar. Part II : case study

Rainfall estimation using polarimetric radar involves the combination of a number of estimators with differing error characteristics to optimize rainfall estimates at all rain rates. In Part I of this paper, a new technique for such combinations was proposed that weights algorithms by the inverse of their theoretical errors. In this paper, the derived algorithms are validated using the "CP2" polarimetric radar in Queensland, Australia, and a collocated rain gauge network for two heavy-rain events during November 2008 and a larger statistical analysis that is based on data from between 2007 and 2009. Use of a weighted combination of polarimetric algorithms offers some improvement over composite methods that are based on decision-tree logic, particularly at moderate to high rain rates and during severe-thunderstorm events.12 page(s

Low pressure systems off the New South Wales coast and associated hazardous weather: establishment of a database

11 page(s

A Robust error-based rain estimation method for polarimetric radar. Part I: Development of a method

The algorithms used to estimate rainfall from polarimetric radar variables show significant variance in error characteristics over the range of naturally occurring rain rates. As a consequence, to improve rainfall estimation accuracy using polarimetric radar, it is necessary to optimally combine a number of different algorithms. In this study, a new composite method is proposed that weights the algorithms by the inverse of their theoretical error. A number of approaches are discussed and are investigated using simulated radar data calculated from disdrometer measurements. The resultant algorithms show modest improvement over composite methods based on decision-tree logic-in particular, at rain rates above 20 mm h-1.12 page(s