Abrupt surface drying and fire weather Part 2: a preliminary synoptic climatology in the forested areas of southern Australia

The climatology and synoptic environments in which abrupt surface drying events, such as those associated with two 2003 and 2005 wildfire events in Australia can occur, are described. Rules to identify such events over six fire seasons indicate that abrupt surface dryings might be expected to occur several times at a given station, although with considerable regional and interannual variability. It is shown that a significant proportion of the events can be associated with mid-tropospheric dry bands clearly identifiable in geostationary satellite water vapour channel imagery, and that the abrupt surface drying is a result of the exchange of this extremely dry air with the surface. Mechanisms that can contribute to this vertical transport are dry convective turbulence in deep daytime mixed layers, vertical circulations associated with frontal circulations, and topographically-induced flows on the downstream side of topographic barriers. Examples of these mechanisms are presented.