Validation of Australian atmospheric aerosols from reanalysis data and CMIP6 simulations.

This study evaluates the performance of different data sources in representing the spatio-temporal characteristics of aerosol species over Australia, which is one of the primary sources of dust in the Southern Hemisphere and an important contributor to global biomass burning emissions. First, NASA/MERRA2 and ECMWF/CAMS Total AOD550nm are evaluated against 16 AERONET stations during 2003–2018, with CAMS consistently under­ estimating (− 15%) and MERRA2 overestimating (19%) the total AOD. Despite the differences in magnitudes, both reanalyses capture the measured Australian aerosols’ seasonal and interannual variability, mainly modu­ lated by seasonal biomass burning and episodic dust storms. CAMS performs remarkably well in low aerosol conditions, while MERRA2 captures extreme aerosol events better. The intercomparison of the different aerosol species from the two reanalyses confirms that CAMS shows lower mean aerosol species concentrations than MERRA2. Results show the greatest differences (more than 50%) in sea salt and sulfates, while organic matter AOD is similarly represented between both reanalyses, with differences of roughly 3%. The spatial distribution and annual cycle of the aerosol types are also compared. In both reanalyses, carbonaceous AOD (black carbon and organic matter) are predominant in the northern part of the country during austral spring, and are highly correlated with MODIS active fires. Dust aerosols prevail in central Australia in summer, and sulfates in the main urban areas throughout the year. However, unlike the other species, sea salt exhibits opposite annual cycles in the two reanalyses. Finally, both MERRA2 and CAMS are used to evaluate the historical simulations of 16 GCM from CMIP6. The models capture the Australian aerosols’ annual variation, although they tend to overestimate dust and underrepresent biomass burning AOD. IPSL-CM6A-LR and EC-Earth3-AerChem perform particularly well simulating aerosols over Australia. The evaluation of Australian aerosols performed in this study could contribute to reanalysis and climate model improvements, as well as improving long-term solar energy resources assessment.

Figure 11. Annual cycles of CMIP6 models, the mean of the models, MERRA2 and CAMS for (a) total AOD, (b) dust, (c) black carbon, (d) organic matter, (e) sea salt, and (f) sulfates. The shaded grey highlight the observation range between MERRA2 and CAMS. in sign.