Diurnal Cycle of Rainfall and Winds near the South Coast of China

The characteristics and mechanisms of diurnal rainfall and winds near the south coast of China are explored using satellite data (CMORPH), long-term hourly WRF Model data (Du model data), a simple 2D linear model, and 2D idealized simulations. Both the CMORPH and Du model data indicate that the diurnal cycle of rainfall has two propagation modes near the coast: onshore and offshore. The diurnally periodic winds (vertical motions) also show a similar propagation feature. Analysis of the rainfall budget indicates that vertically integrated vertical vapor advection plays a key role in the diurnal cycle of rainfall and thus provides a physical connection between winds and rainfall in the diurnal cycle. It was found that a simple 2D linear land-sea breeze model with a background wind can well capture the two propagation modes, which are associated with inertia-gravity waves, in terms of speed and phase. The background wind changes the pattern of the inertia-gravity waves and further affects the diurnal propagation. The effect of the background wind on the diurnal propagation was verified through idealized simulations using a simplified version of the WRF Model that can also capture the diurnal features.