The climatology of Australian tropical aerosol: Evidence for regional correlation

Biomass burning aerosols from the tropical savanna of Northern Australia constitute a globally significant aerosol source, with impacts on regional climate and air quality. Knowledge of the seasonal cycle and spatial distribution of this aerosol is required for its realistic representation in models of global climate, and to help define the role of this region in the global carbon cycle. This paper presents a decadal climatology of these aerosols, based on Sun photometer records from three stations in the Australian tropics, over the period 1998-2012. The monthly time series shows enhanced aerosol emissions following prodigious wet seasons, two of which occurred during the study period. The monthly climatology shows the expected peak during the late dry season (September-November), when most burning takes place, with clear evidence of the dominant modulating effect of fine-particle smoke emission apparent from the annual cycle of the angstrom ngstrom exponent, a proxy for particle size. The aerosol levels during the early dry season are higher at the northern Top End stations than at the south-westerly Kimberley station. The time variation of aerosol optical depth is highly correlated between all three station pairs, with a correlation coefficient r(2)>0.75 at monthly resolution between all pairs. This high correlation between widely separated stations declines only gradually as the filtering interval is reduced, suggesting remarkably high coherence in the emission and transport of biomass burning aerosol across the entire region.