Characterizing Australia's east coast cyclones (1950–2019)

East coast cyclones (ECCs) provide an essential reprieve from dry periods across eastern Australia. They also deliver flood‐producing rains with significant economic, social and environmental impacts. Assessing and comparing the influence of different types of cyclones is hindered by an incomplete understanding of ECC typology, given their widely variable spatial and temporal characteristics. This study employs a track‐clustering method (probabilistic curve‐aligned regression model) to identify key cyclonic pathways for ECCs from 1950 to 2019. Six spatially independent clusters were successfully distinguished and further sub‐classified (coastal, continental and tropical) based on their genesis location. The seasonality and long‐term variability, intensity (maximum Laplacian value ± two days) and event‐based rainfall were then evaluated for each cluster to quantify the impact of these storms on Australia. The highest quantity of land‐based rainfall per event is associated with the tropical cluster (Cluster 6), whereas widespread rainfall was also found to occur in the two continental lows (Cluster 4 and 5). Cyclone tracks orientated close to the coast (clusters 1, 2 and 3) were determined to be the least impactful in terms of rainfall and intensity, despite being the most common cyclone type. In terms of interannual variability, sea surface temperature anomalies suggest an increased cyclone frequency for clusters 1 (austral winter) and 4 (austral spring) during a central Pacific El Niño. Further, cyclone incidence during IOD‐negative conditions was more pronounced in winter for clusters 1, 2, 3 – and clusters 4 and 5 in spring. All cyclones also predominantly occurred in SAM‐positive conditions. However, winter ECCs for clusters 1 and 3 had a higher frequency in SAM‐negative. This new typology of ECCs via spatial clustering provides crucial insights into the systems that produce extreme rainfall across eastern Australia and should be used to inform future hazard management of cyclone events. This article is protected by copyright. All rights reserved

Wave Climate off the Perth Coast: evaluation of an ocean HF radar system and WaveWatch3

Knowledge of the wave climate is important for both economical and environmental motives. Here, we are investigating the wave climate near Rottnest Island, using a combination of observational data (via an HF radar system) and numerical modelling (WaveWatch3). WaveWatch3 facilitates the modelling of wave properties, including directional wave spectra, over a large spatial area. The observations from the Fremantle HF radar station compare reasonably well with the modelling results, inducing confidence in the capability of the radar station to accurately represent the wave climate over mesoscale distances

Wave climate in the Southern Great Barrier Reef, Australia: evaluation of an ocean HF radar system and WaveWatch3

The impact of waves on the environment (e.g. erosion) and industries (incl. shipping and tourism) can be very significant. Here, we are presenting analysis of coastal wave data in the southern Great Barrier Reef (GBR), Australia, using a combination of observational data (HF radar) and a numerical wave model (WaveWatch3). The modeled significant wave height fields compare reasonably well with those obtained from the radar stations, inducing confidence in the two datasets. The radar-produced wave fields are spatially more variable compared to the model results, linked to the influence of wind stress resolution and currents in accurately determining wave characteristics

Wave and wind parameters from HF ocean radar

A sparse network of surface current and wave-capable HF radars is being established around the Australian coastline to produce quality controlled data into a public-domain archive under the umbrella of the Integrated Marine Observing System (IMOS). The phased array installations\ud within the Australian Coastal Ocean Radar Network (ACORN) produce maps of significant wave heights, and wind directions, and under good signal-to-noise conditions, generate directional wave spectra.\ud \ud The radar installations are always made in matched pairs, spatially separated so that the beams formed by the phased arrays cross at a non-acute angle in the primary area being mapped; this gives the 2-D capability of each radar pair. Phased-array stations are installed at the Capricorn/Bunker Groups, QLD (Tannum Sands, and Lady Elliot Island); the entrance to the South Australian Gulfs, SA (Cape Wiles, Eyre Peninsula and Cape Spencer, Yorke Peninsula);\ud Rottnest Area, WA (Port Beach, Fremantle and Guilderton); and Coffs Harbour, NSW (Red Rock and North Nambucca)

Spatial averaging of HF radar data for wave measurement applications

HF radar data are often collected for time periods that are optimized for current measurement applications where, in many cases, very high temporal resolution is needed. Previous work has demonstrated that this does not provide sufficient averaging for robust wave measurements to be made. It was shown that improvements could be made by averaging the radar data for longer time periods. HF radar provides measurements over space as well as in time, so there is also the possibility to average in space. However, the radar data are correlated in space because of the range and azimuth processing. The implications of this are discussed and estimates of the impact on the reduction in variance in the radar Doppler spectral estimates are obtained. Spatial inhomogeneities and temporal nonstationarity in the ocean wave field itself also need to be taken into account. It is suggested that temporal averaging over periods of up to one hour and spatial averaging over 9–25 nearest neighbors may be suitable, and these will be explored in later work

Teleconnection of atmospheric and oceanic climate anomalies with Australian weather patterns: a review of data availability

The quality and quantity of observed and reanalysed data influence the direction and accuracy of scientific research. This paper reviews the data available for the study of climate and weather patterns in Australia. A list of global reanalysis and satellite data is provided, along with a more detailed review of available in situ (weather station) data in Australia. Regularly updated climate indices are identified that have previously been linked to Australian climate and weather events. Observation of Australian weather is severely hampered by the continents' vastness and remoteness, as evidenced by heavy bias of in situ measurements that are generally clustered in the coastal high-population centres (mainly southeast of Australia), with central and northern regions often having to rely on remote sensing and reanalysis data. Data sparsity can introduce significant uncertainty in terms of extreme weather and climate change management, as variables such as rainfall exhibit high spatial and temporal variability. Several areas for future research are identified, including investigation into the impact of Australian aerosol levels, the connection between soil moisture and flooding potential, and teleconnection between Atlantic sea surface temperature and Australian climate. While this study focusses on data availability to investigate Australian climate patterns, findings are applicable at a global scale

Hydrological characteristics of Australia: relationship between surface flow, climate and intrinsic catchment properties

Streamflow and baseflow dynamics are driven by complex, interconnected catchment properties. A national study was conducted to assess the relationship between surface flow, climate and intrinsic catchment attributes in Australia. Subcatchments were delineated based on Horton's 5th stream order and were characterised by identifying parameters that influence streamflow and flood behaviour. Because observational datasets like rainfall and streamflow commonly have a non-normal distribution, the method of L-moments was applied to several time series. Surface hydrology and baseflow patterns were represented by twenty indices, which were statistically summarised via principal component (PC) analysis, yielding six PCs. Forty catchment descriptors from the themes of climate, topography, surface condition and hydrogeology were used to investigate their link with runoff patterns. Among these is the land surface value, a newly defined index incorporating soil properties and land use to estimate the capacity for water infiltration. All metrics were explored via correlation and regression analysis against the surface hydrology PCs and their influence on runoff discussed. The predictive skill of the regression models is improved when non-perennial waterways are excluded. Although rainfall characteristics dominate streamflow behaviour, topographical and surface conditions also greatly impact on runoff, especially during low-flow periods

Nitrate and ferrous iron concentrations in the lower Burdekin aquifers: assessing denitrification potential

The lower Burdekin is one of Australia’s premier irrigation districts with more than 80,000 ha of sugarcane and other crops. Because it is located adjacent to the Great Barrier Reef Lagoon, there is strong interest in understanding the fate of nitrogen applied as fertiliser. Natural denitrification is increasingly recognised for its ability to reduce nitrate concentrations in groundwater and we therefore analysed water samples for a range of constituents (nitrate, ferrous iron, dissolved oxygen, redox potential, pH) from 57 monitoring bores to investigate the denitrification potential of the lower Burdekin aquifers. Nitrate concentrations ranged from <0.1 to 14.4 mg/L NO3-N (three times the ANZECC environmental standard of 5 mg/L). Ferrous concentration varied from 1 to 360 mg/L, dissolved oxygen was < 2 mg/L, redox potential varied from -120 to +235 mV, and pH ranged from 5.9 to 7.6. Elevated nitrate levels were observed in 16% of the bores located mostly in the Home Hill area. These areas also had low ferrous levels. High ferrous levels were found mostly in the Ayr area and at shallow depths. The data in general showed an inverse relationship between nitrate and iron, and between nitrate and ammonium. Furthermore, undetectable amounts of nitrate were measured in the nested bores located along the coast. These geochemical conditions favour the presence of ferrous iron and a reduced environment conducive to denitrification. These results suggest that denitrification is one of the mechanisms involved in reducing the amount of nitrate in the lower Burdekin aquifers and hence reducing the potential for nitrate to move from the groundwater into the near-shore marine environment