The Diurnal Cycle of Convection in Papua New Guinea and Its Offshore Propagation: The Role of Monsoons, Land Breezes, and Cold Pools

Understanding the diurnal cycle of convection near tropical islands presents numerous challenges due to the complex interaction between ocean, land, and atmospheric processes. The delicate interplay of these actors leads to diurnally varying precipitation and widespread offshore propagation (OP) around islands. Papua New Guinea is one of the largest tropical islands in the world and has received less attention than other islands. With elevations exceeding three kilometers, convection on the island exhibits an afternoon maximum in land-based precipitation, an early-morning rainfall maximum, and dynamic offshore propagation events northeast of the island. However, the details of these processes and their underlying mechanisms remain unclear.

This study addresses these issues using both observational data and realistic simulations. First, Global Precipitation Measurement (GPM) data is utilized to establish the climatology of diurnal offshore convection around New Guinea. Second, convection-permitting Weather Research and Forecasting (WRF) simulations are employed to analyze the multiscale density currents that significantly contribute to offshore propagation over the warm ocean. The cross-equator monsoon significantly influences the daily variability of OP in February by impacting the wind field and acting as a large-scale source of dry air that interacts with the diurnal cycle. Additionally, land breezes serve as a major dynamic source for diurnal OP, creating moist patches at their edges, similar to precipitation-driven cold pools that develop later, which facilitate convective propagation. These findings underscore the critical roles of monsoon, land breeze, and cold pools and their interactions within the moist boundary layer dynamics.