Precipitation Diurnal Cycle over the Maritime Continent Modulated by the Climatological Annual Cycle

The modulation of the diurnal cycle (DC) of precipitation over the Maritime Continent (MC) by the background annual cycle mean state was studied for the period of 1998-2014 through observational analyses and high-resolution simulations using the Weather Research and Forecasting (WRF) Model. The observational analyses reveal that there are statistically significant differences in the DC amplitude between boreal winter and summer. The amplitude of precipitation DC reduces by about 35% during boreal summer compared to boreal winter, especially over the MC major islands and adjacent oceans. A precipitation budget analysis indicates that the DC amplitude difference is primarily attributed to vertically integrated convergence of the mean moisture by diurnal winds. The relative roles of the background dynamic and thermodynamic states in causing the enhanced diurnal wind activity in boreal winter are further investigated through idealized WRF simulations. The results show that the seasonal mean background moisture condition is most critical in inducing the winter-summer difference of the precipitation DC over the MC, followed by atmospheric static stability (i.e., vertical temperature gradient) and circulation conditions.

Automated summary

Observational analyses and high-resolution simulations using the WRF Model revealed significant differences in the diurnal cycle amplitude of precipitation between boreal winter and summer over the Maritime Continent. Additionally, a precipitation budget analysis suggested that the DC amplitude difference is primarily influenced by the convergence of mean moisture by diurnal winds. Further investigations through idealized WRF simulations indicated that the seasonal mean background moisture condition plays a critical role in the winter-summer difference of the precipitation DC over the MC.