Assessment of Temperature and Humidity Changes Associated With the September 2009 Dust Storm in Australia

A historic dust storm affected the eastern portions of Australia between September 22 and 24, 2009, causing significant reductions in air quality and visibility. Using multiple satellite remote sensing data sets and meteorological information, we assess the distribution of dust aerosols and their potential effects on the Earth-atmosphere system. Spaceborne active lidar data showed that dust aerosols were located up to 2 km above the surface. The thickness of the dust plume (0.55-μm aerosol optical thickness >; 1.0) reduced surface visibility to below 2 km. Dew-point depressions of 20 <;sup>;°<;/sup>;C or more occurred after passage of the dust plume, with decreases in surface temperature observed at some locations. Between the surface and 2-km level, temperature data show a cooling of ~10°C in the hours after passage of the cold front along which dust aerosols had converged. However, much of the temperature change that occurred is a result of cold air advection behind the northward traveling plume. Radiative transfer modeling suggests that only up to 1°C per day of this cooling is due to the decrease in solar radiation reaching the surface layer. Radiative transfer modeling also indicates a net warming of up to 2°C per day within and above the dust layer, possibly offsetting some cooling aloft due to the cold front passage. Modeling results indicate that expected aerosol radiative effects to temperature are small compared to synoptic influences and are unlikely to be sampled in observations under this scenario since the magnitudes of these effects are quite small.