Evaluation of aerosol representation by ACCESS-CM2 with increased aerosol-chemistry complexity in the Southern Ocean
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2020
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Melbourne Authors
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School of Earth Sciences
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Masters Coursework thesis
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Open Access
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© 2020 Imogen Wadlow
Abstract
This thesis identifies the inherent biases of aerosol parameters within the next-generation Global Climate Model (GCM); the Australian Community Climate and Earth System Simulator Coupled Model (ACCESS-CM2). GCMs poorly represent clouds and aerosols over the Southern Ocean, resulting in systematic shortwave (SW) radiation biases with widespread global energy budget impacts. This research determines whether a more complex, physically-representative aerosol-chemistry scheme may reduce the Southern Ocean radiation bias, and the inherent aerosol biases established within ACCESS-CM2.
Southern Ocean aerosols are dominated by sea-salt and biogenic products. This study ran a control ACCESS-CM2 simulation and three perturbation simulations, which altered either the representation of Primary Marine Organic aerosols, sea-salt, or implemented a fully interactive chemistry scheme respectively. A suite of ground-based and satellite observations was collected and compared against each simulation to establish model bias respective to key aerosol metrics including Aerosol Optical Depth (AOD), Cloud Con- densation Nuclei (CCN) and SW radiation. Simulation biases were explained through model-observation comparisons of aerosol chemistry, size and number parameters.
Overall, ACCESS-CM2 exhibited a substantial positive bias in Aerosol Optical Depth (AOD) and SW radiation, and underestimated Cloud Condensation Nuclei concentration. This research suggests that increasing the complexity of aerosol schemes was able to provide a closer model agreement with observed aerosol metrics of AOD and CCN. Fully interactive chemistry provided the best reduction in both AOD and CCN bias. However, modified aerosol schemes have negligible effects upon the inherent SW radiation bias in ACCESS-CM2, suggesting further research into cloud schemes is necessary.
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Aerosol, aerosols, clouds, Southern Ocean, Aerosol Optical Depth, Cloud Condensation Nuclei, climate model, climate modelling, ACCESS, ACCESS-CM2, atmospheric chemistry