The climatology of Australian tropical aerosol: Evidence for regional correlation

Abstract

[1] 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 Ångström 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.

The Climatology of Australian Aerosol

“…The extent to which such coherence applies on shorter timescales is unclear, although its persistence among tropical stations was explored by Mitchell et al (2013). Although a monthly climatology is useful for low-frequency applications, including solar resource prediction and arguably climate change, it is by no means suitable for applications requiring instantaneous aerosol fields such as the atmospheric correction of remote sensing imagery from satellites.…”

“…Australia is the largest dust source in the Southern Hemisphere (Tanaka and Chiba, 2006) and is a significant source of smoke aerosol from savanna burning (Mitchell et al, 2013). Hence, it is clear that Australia's aerosol emissions make up a significant fraction of the Southern Hemisphere total.…”

“…While coastal maritime aerosol has been extensively studied (Gras and Ayers, 1983;Gras, 1991), studies of the continental aerosol are more restricted. Thus, Scott et al (1992) characterised the aerosol cycle caused by seasonal biomass burning at Broome in the tropical northwest of Australia in the late 1980s, with more extended analysis of regional tropical aerosol carried out by Mitchell et al (2013); see also references cited therein, including Bouya et al (2010). Studies of the smoke from eucalypt fires in southern temperate forests are few in number, but include Mitchell et al (2006) and Radhi et al (2006).…”

Fire in Australian savannas: from leaf to landscape

“…In a similar experiment for equatorial Asia, touching on northern Australia, Tosca et al (2010) found similar feedback mechanisms. In Mitchell et al (2013), recent observational data are presented that give evidence for a fairly homogeneous distribution of elevated fire-induced aerosol levels during the late dry season.…”

The Climatology of Australian Aerosol

“…While coastal maritime aerosol has been extensively studied (Gras and Ayers, 1983;Gras, 1991), studies of the continental aerosol are more restricted. Thus Scott et al (1992) characterised the aerosol cycle caused by seasonal biomass burning at Broome in the tropical north west of Australia in the late 1980s, with more extended analysis of regional tropical aerosol carried out by Mitchell et al (2013); see also references cited therein. Studies of the smoke from Eucalypt fires in southern temperate forests are few in number, but include Mitchell et al (2006) and Radhi et al (2006).…”