Summertime precipitation over northern Australia in AMIP simulations from CMIP5

Tropical precipitation is caused by many processes that occur over a wide range of temporal and spatial scales. Such processes vary from local, diurnal convection driven by a destabilisation of the boundary layer to planetary-scale systems that result in rainfall over many days. It is therefore important to assess whether general circulation models (GCMs) can represent these processes given that such models are routinely used to project future rainfall in the low latitudes. In this study, we evaluate the rainfall and circulation characteristics of ten GCMs from the Coupled Model Intercomparison Project Phase 5 (CMIP5) over northern Australia. This work shows that the diurnal cycle of the low-level (925 hPa) flow around the heat low is represented well by the models but the timing of precipitation is not (triggered too early). There is also evidence that mid-level synoptic systems that are responsible for initiating rain in the observations are also present in all of the models. Nevertheless, the biases in the modelled seasonal mean precipitation seem to be linked to the strength of both the meridional flow into northern Australia and the vertical mass flux. Furthermore, there is also evidence that the representation of convection in these models is likely contributing to both the precipitation and circulation errors over northern Australia.