Impact of high-resolution air-sea interactions on the Australian climate

We have developed a Regional Coupled Model for the Australian region based on NEMO-OASIS-WRF (NOW) at 1/4° resolution. This is used to assess the importance of resolving high-resolution air-sea interactions at the mesoscale 0(100 km) in representing the oceanic circulation around Australia and key features of the Australian climate. Australia has very diverse climatic regions and is affected by a variety of extreme events such as storms, droughts, atmospheric and marine heatwaves. Amongst those regions, the east coast of Australia is particularly impacted by persistent low-pressure systems, commonly known as the East Coast Lows (ECLs) that are associated with intense rainfall and often cause considerable damage. The sensitivity of these ECLs to the mesoscale air-sea interactions are studied using a hierarchy of simulations performed with the NOW model. First, the ocean current feedback is suppressed to investigate how mechanical exchanges contribute to the statistics of ECLs. Then, the sea surface temperature (SST) is smoothed during the coupling to analyse how the thermal feedback of small-scale SST modifies the ECLs. Finally, the SST taken from a fully coupled run is used to force an atmosphere-only model. The latter simulation serves to assess how current dynamical downscaling methods represent the ECLs, temperature and precipitation patterns over Australia, compared to a fully-coupled model including mesoscale air-sea interactions.