Model Fidelity of Multi-scale Variability over the Maritime Continent

The Maritime Continent (MC) represents a critical region of multi-scale interactions, key to local as well as remote weather and climate variability. It is essential that global models represent these interactions with high fidelity to achieve skillful weather and climate forecasts. In this study, the twenty-year climate simulations from the GEWEX Atmospheric System Study (GASS) and Year of Tropical Convection (YOTC) multi-model experiment are used to assess contemporary model performance over the MC. Of particular interest of this study is the representation of the diurnal cycle of precipitation, including its interactions with synoptic intraseasonal and seasonal variability. Model performance is assessed using metrics that utilize the mean precipitation pattern and the magnitude and phase of the diurnal cycle. Furthermore we examine cross model differences to gain insight into key processes that need to be represented in a model in order to realistically represent these multi-scale interactions. The analysis focuses on 4 land regions (Sumatra, Borneo, New Guinea and Southeast Asia) and 4 ocean regions (Eastern Indian Ocean, West of Sumatra, between Sumatra and Borneo and Banda Sea) which are found to be characterized by large, albeit varying relative, amplitudes of the mean and diurnal harmonic of the precipitation. In addition, it was found that a phase of the diurnal cycle differs between regions but is constant within each of them. Preliminary results for example show that of the 22 models analyzed, about ¼ have good representation of the diurnal cycle – including the relative size of diurnal amplitude to the mean and how they represent the similarities and differences between the land and ocean diurnal cycle. Most models perform well in representing seasonal cycle of mean precipitation patterns. However, realistic seasonal cycle of the diurnal cycle is still challenging to the models. These results will be discussed along with additional highlights from our ongoing comprehensive assessment of model performance over the MC. This work is being done in support of the WWRP-WCRP Subseasonal to Seasonal Project's Subproject on interactions between the MJO and the MC.