This study investigates the diurnal cycle of convection over the northern South China Sea (SCS) during the 1998 Southeast Asian summer monsoon, using reflectivity and instantaneous rain rate data from the BMRC C-POL radar on Dongsha Island, and geometrically-corrected GMS-5 satellite IR brightness temperatures. Using Hovmöller diagrams of IR brightness temperature, the most convectively active period over the northern SCS (15 May-10 June) was logically subdivided into three active subperiods (15-20 May, 21-31 May, 1-10 June) based on the repetitive convective nature of each subperiod and the abrupt shift between subperiods. Each subperiod contained several convective events on the mesoscale with a high degree of daily repetition.

Satellite proxies, such as brightness temperature minima and deep convective activity (Hendon and Woodberry, 1993) maxima, were used to determine the diurnal characteristics of the convection over the northern SCS. In general, the maximum convective activity occurred during the early to mid-morning hours in areas adjacent to the southeastern China coast, but later in the afternoon as distance from the coastline increased. This was verified by radar reflectivity and rain rate data for the region surrounding Dongsha Island, and by rain gauge data on the island itself. Evolutionary histograms (e.g. Morcrette 1991) of brightness temperature indicated that the highest clouds preferentially occurred during the afternoon hours, while clear-sky conditions occurred most often during the late evening and night. Following a technique similar to Liberti et al. (2001), this afternoon maximum of convection was attributed to a propagation of convective systems in a direction perpendicular to and away from the China coast.