Near Real-time Forecast using a Global Nonhydrostatic Model for a Field Campaign in the Maritime Continent

A global nonhydrostatic model is a useful tool to investigate interactions among diurnal to subseasonal variabilities in the tropics. Nonhydrostatic Icosahedral Atmospheric Model (NICAM) have been used for studies on extended-range forecast of tropical cyclogenesis, Madden-Julian Oscillation (MJO), and also for near real-time forecast during field campaigns. In 2015, a field campaign was conducted in the southwest Sumatra during November to December 2015 by JAMSTEC, aiming for better understanding of the diurnal cycle and its interaction with various variabilities in the Maritime Continent region. The campaign serves as a pilot study for the forthcoming observation plan, “Years of the Maritime Continent (YMC)” project. Near real-time forecast using NICAM were routinely run for the observation period and in boreal summer. El Nino and positive phase of Indian Ocean Dipole kept developing since early summer over the Indo-Pacific domain, which led to negative anomalies of sea surface temperature (SST) off shore of the southwest Sumatra. These might affect convective behavior in 2015 as the background state. The model well captured convectively-coupled vorticity disturbances and their development into tropical storms over the western Pacific in boreal summer, and their modulation associated with intraseasonal variability (ISV) is roughly represented. In the early stage of the observation period, westward propagating vorticity disturbances repeatedly crossed the Maritime Continent region in the active phase of the ISV/MJO. Comparison of the forecast skill of these phenomena with those in the operational models which are provided by the WMO/WCRP/WWRP project for sub-seasonal to seasonal prediction (S2S) is also discussed.