Journal of Southern Hemisphere Earth Systems Science

A newly discovered erosional scar on the Nullarbor Plain in southern Australia reveals the immense power of tornadoes in shaping the landscape. This scar, identified by satellite imagery, stretches 11 km and is marked by distinct cycloidal patterns, indicating it was formed by a tornado with estimated wind speeds exceeding 200 km h^–1. These findings underscore the importance of using modern technology to understand and track tornado activity in remote regions, aiding in better prediction and preparedness for such destructive events.

This summarises the southern hemisphere atmospheric circulation patterns and meteorological indices for 2019–20; an account of rainfall and temperature for the Australian region is also provided. The second half of 2019 was dominated by a strong positive Indian Ocean Dipole, before a return to more normal conditions from early 2020. Australia was exceptionally dry in the second half of 2019, which contributed to an extreme fire season. Temperatures were well above average in Australia and the hemisphere as a whole.

This is a seasonal climate summary for autumn 2020, detailing the weather and oceanic conditions and events for March, April and May. During this period south-east Australian rainfall led to flooding and extinguished the remaining fires of the 2019–2020 bushfire season, and 2020 marked the second time that the Great Barrier Reef experienced mass coral bleaching due to elevated ocean temperatures in an ENSO neutral year.

Extratropical lows and east coast lows cause a large proportion of rainfall in southern Australia during the months May–October. Their frequency varies from year to year, but new data show that they have been becoming less common in recent decades compared to the 1960s. This is contributing to decreases in cool season rainfall in southern Australia. (Image credit: Acacia Pepler.)

The planetary boundary layer height (PBLH) measurements are rare at the Great Barrier Reef (GBR), limiting our ability to evaluate weather, climate and air pollution models in this significant region. Here we show that drone-based sampling and Mini-Micropulse (MP) LiDAR, are complementary ways of calculating the PBLH at the GBR. We find the boundary layer to be consistently stable and well-mixed during the campaign, with good congruence between the thermodynamical-derived drone PBLH, and the backscatter-derived MP LiDAR PBLH.

We develop and present a dataset that helps quantify how much more often coastal floods will occur as sea-level rise continues and accelerates. Our dataset is designed so that it is adaptable to any local context, considering relevant planning guidelines, adaptation triggers and flood impacts of concern. Our dataset is analysed to show that once-a-century floods are expected to become chronic occurrences at 85% of Australian locations studied under 1-m sea-level rise.

Grain production from south-west Western Australia (SWWA) is heavily dependent on rainfall. The Southern Annular Mode (SAM) has been linked to SWWA rainfall variability. This study evaluates growing season rainfall forecasts in SWWA and the simulation and prediction of SAM, using the Australian Bureau of Meteorology’s seasonal forecasting model (ACCESS-S2). The results show limited forecast skill for rainfall but generally good forecast skill for SAM. These results highlight the low predictability for SWWA rainfall and suggest other factors may be limiting model skill rather than the model’s ability to capture SAM.

A new convection scheme, ‘CoMorph-A’, has been introduced into the latest UK Met Office coupled (GC4) and atmosphere-only (GA8) models. Our results show improvements over the Indo-Pacific and northern Australian regions, as well as significant improvements in the rainfall bias, Madden–Julian Oscillation simulation and prediction, tropical cyclone forecasts and the diurnal cycle of rainfall over the Maritime Continent. The use of this new convection scheme is promising for improving the simulation and prediction of Australian weather and climate.

The impacts of tropical cyclone rainfall on the northern coastlines of Australia can be severe. Trends for widespread and localised cyclone rainfall are examined in this paper in three historical datasets using innovative methods. There was a general disagreement in trends and average recurrence interval for the different measures of cyclone rainfall between datasets. By contrast, an increase in the fractional contribution of cyclone rainfall was more consistent between datasets, particularly over the north-western coastal region of Australia.

Fog has a big effect on aviation and two case studies are presented to investigate the role of topography on the local circulation and fog formation at Perth Airport. The main finding was that the northerly near-surface winds stem from a blocking of the airmass in the lower levels by the Darling Scarp. The light near-surface winds in combination with nocturnal surface cooling and moisture from the environmental flow create conditions favourable for the development of fog at Perth Airport.

The merging of weather radar data with rain gauge data offers a practically usable and affordable technology to interpolate rainfall amounts at fine spatial resolution between sparsely located rain gauges, particularly in rain-fed agricultural regions. This work details the provision of rainfall maps at high spatial and temporal resolution at the agricultural field scale. Knowledge of the spatial variability of rainfall at the field level can support precision agriculture management strategies for the growing of dryland crops and pastures.