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Linear precipitation systems are a prominent contributor to rainfall over Melbourne, Australia, and the surrounding region. These systems are often convective in nature, frequently associated with cold fronts, and in some cases can lead to significant rainfall and flash flooding. Various types of linearly organized systems (e.g., squall lines, quasi-linear convective systems) have been the subject of much research in the United States and elsewhere, but thus far relatively little analysis has been done on linear systems in Australia. To begin to understand rainfall extremes and how they may change in this region in the future, it is useful to explore the contribution of these types of systems and the characteristics that define them. To this end, we have examined the recently developed Australian Radar Archive (AURA), identifying objects that meet a specific set of relevant criteria, and used multiple methods to identify heavy and extreme daily rainfall. We found that on average, days with linear systems contribute over half of the total rainfall and 70%–85% of heavy/extreme rainfall in the Melbourne region. The linear systems that occur on heavy rainfall days tend to be larger, slower-moving, and longer-lived, while those on extreme rainfall days also tend to be more intense and have a greater degree of southward propagation than linear systems on other days. [ABSTRACT FROM AUTHOR]

The southern Nullarbor Plain is covered by low amplitude (generally 1–2 m) parallel ridges and swales with variable wavelength (300–900 m). The ridges are stony; the swales hold thin deposits of unconsolidated silt and clay. The ridges and swales have previously been attributed to joint control but are not parallel to joints exposed in cave roofs. Instead, they have a striking similarity to central Australian linear sand dunes: they are parallel, regularly spaced and most importantly, fork in a consistent direction. They are here explained as the etched footprints of an extensive linear dune system that once covered much of the southern Nullarbor. Rainwater collecting in the troughs between the sand dunes dissolved the underlying limestone to produce the swales. Recognition of this dune field fills a major gap in the distribution of linear dunes across Australia. The dunes have subsequently disappeared, apart from red aeolian sand in dolines in the southeastern part of the Nullarbor; most of the sand was probably blown offshore. The ridge and swales are oriented predominantly north-south in the west, and northeast-southwest and northwest-southeast in the centre and east, due to deposition by northerly and westerly winds respectively, as shown by directions of forking. The north-south Nullarbor dunes are probably older and may have been deposited in the arid climate of the late Neogene; this would make them the oldest linear dunes in Australia, remnants of an early phase of linear dune activity that has been removed or overprinted elsewhere. The change in wind direction shown by the dune orientation could represent northward migration of sub-tropical high-pressure systems during the late Neogene. • The southern Nullarbor Plain is covered by low amplitude parallel ridges and swales. • The ridges and swales represent the etched footprints of a linear dune system. • The north-south dunes were perhaps deposited by late Neogene northerly winds. • Such Late Neogene north-south dunes would be the oldest linear dunes in Australia. [ABSTRACT FROM AUTHOR]