Modelling dust transport over Central Eastern Australia

The local or long-range transport of dust by wind erosion, events most commonly referred to as dust storms, are a regular occurrence over much of central eastern Australia. Annual dust storm frequencies over Australia for the period 1957 to 1984 can be as high as 5 to 10 times per year in some areas. Australian dust storms may be divided into two groups with distinct dust storm seasons, namely, spring-summer (September-February) and summer-autumn (December-May). Dust storms can be further subdivided into two types; those that result in the local dust transport and those that produce long-range dust transport. Local dust transport typically occurs over periods ranging from a few minutes to a few hours as a result of short-lived, extreme wind speeds generated, for example, by thunderstorms. Long-range dust transport occurs on longer time scales and on spatial scales ranging from hundreds to thousands of kilometres usually with the passage of frontal systems. In prolonged dust storm episodes, wind erosion has a dramatic effect on the air quality in regions downstream of the dust sources, reduce the quality of the topsoil, play an important role in the global dust cycle and disrupt social and economic activities. In this study we focus on long-range dust transport from 1995 to February 2005 as identified from dust reports at Bureau of Meteorology synoptic reporting stations over central eastern Australia.

A climatology of dust reporting days from 1995 to February 2004 in central eastern Australia reveals a total of 55 days consisting of 43 associated with fronts of which 24 were classified as embedded in the zonal westerlies in the Great Australian Bight (GAB) or in westerlies derived from low pressure systems in the GAB. The remaining 19 were associated with fronts over eastern Australia where high pressure systems in the GAB controlled postfrontal south to southeast winds. Three case studies of dust storm generation and transport were modelled using an integrated wind erosion prediction system. The model predictions were broadly consistent with both satellite images highlighting dust and the synoptic observations reporting dust. Representation of antecedent land surface conditions is critically important in generating dust and in providing good model predictions of dust transport.