The Diurnal Cycle of Convection over the Northern South China Sea

The diurnal cycle of convection over the northern South China Sea (SCS) during the onset of the summer monsoon is documented using data from the May-June 1998 South China Sea Monsoon Experiment (SCSMEX) and from ten years of observations from the Tropical Rainfall Measuring Mission (TRMM) precipitation radar. Results both during SCSMEX and from TRMM observations show a prominent signal of propagating convection over the northern SCS. In particular, convection is found to initiate just off the southern coast of mainland China near sunrise and propagate southeastward at about 10-15 m s(-1) to the central part of the northern SCS the early afternoon, finally dissipating about 500 km offshore in the late evening. Both indirect measures, such as infrared brightness temperatures and areal cold (< 208 K) convective cloud coverage, and direct measures, i.e., radar reflectivities from the Bureau of Meteorology Research Centre (BMRC) and TRMM radars, show this behavior. The radar data indicate an increasing stratiform contribution to total precipitation as the convective systems move farther offshore, indicative of maturing mesoscale convective systems. Neither advection nor gravity current processes appear to explain the offshore propagation of the envelope of convection, suggesting gravity wave dynamics, possibly associated with discrete propagation, as a factor in the system motion.