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Climate Chemistry

We use the UKCA (UK Chemistry and Aerosols) model within the ACCESS (Australian Community Climate and Earth System Simulator (ACCESS) framework to include and understand the role of chemical cycles of reactive gases (e.g. ozone and methane), aerosols, and their interactions, that have important (radiative) feedbacks on the current state and the predictions of the future state of the Earth’s climate. UKCA includes both tropospheric and stratospheric chemistry.

The inclusion of coupled chemistry as an Earth System component within ACCESS (together with the CABLE land-surface scheme and the MOM ocean model components) enables investigation of a range of topics including climate-chemistry-aerosol interactions and process understanding, e.g. the impact of near-term climate forcers (methane, ozone and aerosols), nitrous oxide and ozone-depleting halocarbons. Currently ACCESS-UKCA is configured to run in atmosphere-only mode, with a particular focus on the Southern Hemisphere.

We also have the capability to compile global emission databases for ACCESS-UKCA, include atmospheric nudging for process understanding, and developed model evaluation suites with data from the Cape Grim Baseline Air Pollution Station and from other global sites. We have developed an ocean ozone deposition scheme and included it in ACCESS-UKCA, with significant consequences on tropospheric ozone. A parameterisation for marine aerosols has also been included, and studies are underway to understand the Antarctic ozone hole and linkage with other climate drivers, and tropospheric ozone changes, budgets and governing processes (e.g. deposition and lightning), Southern ocean aerosols, and oxidative capacity of the troposphere.

UKCA modelled ozone dry deposition velocity (cm/s) to the ocean for the year 2006 obtained using the original dry deposition scheme (top plot) and a new mechanistic dry deposition scheme (Luhar et al., 2017, 2018) (bottom plot). The new scheme reduces the global oceanic ozone dry deposition to a third of the original amount, with consequences on the tropospheric ozone burden.

 

We have included a parameterisation for marine organic emission based on Gantt et al. (2011; 2015) in UKCA. This plot shows the significant differences resulting from including primary and secondary marine organics in cloud droplet number (CDN) (top plot) and top of atmosphere short wave (TOA SW) radiative effect (bottom plot), from nudged one year UKCA simulation.