The "Red Dawn" dust storm on 22 and 23 September 2009, called "Red Dawn", was the largest to pass over Sydney in term of reduced visibility (400 m) since reliable records began in 1940. The maximum hourly PM 10 concentration measured near Sydney was 15,366 μg/m 3 at Bringelly and is the highest ever recorded for Sydney and possibly any Australian capital city. The Australian air quality standard of 50 μg/m 3 per 24 hours was massively exceeded at Randwick (1,734 μg/m 3) and Newcastle (2,426 μg/m 3). Red Dawn was caused by drought and the extreme wind conditions caused by a low pressure trough and cold front associated with a deep cutoff low pressure system. The source of the dust was the red sandplains of western New South Wales, the sandplains, riverine channels and lakes of the lower Lake Eyre Basin and Channel Country of Queensland. Between 22 September 2009 at 1400 to 23 September 2009, 0.3 Mt of PM 10 dust was transported off the coast between Albion Park and Newcastle (182 km length) near Sydney. The maximum hourly rate of PM 10 dust lost off the coast near Sydney was 71,015 t/h on 22 September at 2100. Calculating the total suspended particulate sediment lost off the Australian coast for the 3000 km long Red Dawn dust storm gives an estimate of 2.54 Mt for a plume height of 2500m. This is the first and largest offcontinent loss of soil ever reported using measured, as apposed to modelled, dust concentrations for Australia.
Field experiments using a sand particle counter and an optical particle counter clarified the links between saltation and dust emission under wet and weakly crusted conditions in a fallow field previously cultivated with wheat in Australia. A crust was formed by the impact of raindroplets after small precipitation events. A little soil moisture enhanced the strengths of crust and aggregation even though the soil was dried. Dust concentration was proportional to friction wind velocity, but the proportionality was dependent on ground surface conditions, such as the minimally dispersed particle size distribution of parent soil and the presence or absence of crust.
Extruded rice crisps were adjusted to water activities in the range of 0.05–0.65, and texture measurements were carried out by single compression or compression of a layer of 10 specimens. Sensory crispness ranking was performed by a panel familiar with texture evaluation. Several parameters were derived from the force/displacement curves, and a crispness indicator was calculated on the basis of the relationship between the texture parameters and water activity. This crispness indicator showed best correspondence sensory results, especially when layer compression was performed.
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