Seasonal Cycles in Aerosol Optical Properties in Darwin
Atmospheric aerosols are highly variable in space and time, and knowledge of this variability is important for a variety of applications. We have investigated the seasonal cycles in aerosol properties in Darwin using Multifilter Rotating Shadowband Radiometer (MFRSR) optical thickness measurements obtained from the Tropical Western Pacific (TWP) facilities site in Darwin, part of the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Program.
Regression analysis of the Darwin data for the period March 2002 to June 2003 shows a strong seasonal cycle in aerosol optical thickness, with marked periods of low optical depth during autumn (March-May) and periods of high optical depth during spring (September-November). The periods of high optical depth coincide with the biomass burning season in the north. The aerosol optical thickness and Angstrom coefficient seasonality were strongly correlated with the meteorological parameters. Comparisons with aerosol optical properties from independent aerosol measurements by other authors showed generally good agreement
The aerosol optical depth measurements for 323 cases, representing days with clear stable morning and/or afternoon, were inverted to obtain the size distribution. The aerosol size distributions show seasonal variations, differences between mornings and afternoons, and strong correlations with wind speed and direction.
An intensive study of the biomass burning season measurements and their correlation with the fire regime in the Australian Northern Territory and the local meteorology was carried out. Results show that the aerosol loading is influenced by the meteorology and strongly linked to the fire activity in the north.