Diurnal Cycle of Convection Over the Maritime Continent and Indo-Pacific Warm Pool: Houze's Early Work and Recent Results

Deep convection over tropical oceans has the peculiar trait that it tends to peak around sunrise, in sharp contrast to afternoon convection over land. Although many studies offered various explanations for this over the years, Bob Houze’s approach focusing on mesoscale convective system (MCS) structure and time evolution stood out. Observations by Houze et al. (1981) during WMONEX near Borneo provided a first description on how development of MCSs affected by land breeze and interacted with the monsoon circulation led to the maximum of convection in the morning hours several hundred kilometers from the coast. Later, through tracking of MCSs during TOGA COARE, Chen and Houze (1997) revealed that the life cycles of large MCSs contributed to the nocturnal maximum of convection over the open ocean in the West Pacific warm pool. MCSs were initiated in the afternoon and reached their largest areal extent in the early morning. These results inspired our recent study using TRMM rainfall data along with tracking of MCSs from hourly IR data. It is found that there are significant regional differences between the marginal seas over the Maritime Continent, the Indian Ocean, and the western North Pacific. The Indian Ocean-western North Pacific warm pool has a rainfall maximum just after midnight, several hours before the largest MCSs reach their maximum areal extent. Over the Maritime Continent seas, the rainfall maximum occurs several hours later in the morning and is more pronounced. The diurnal cycle of convection over the islands and seas in the Maritime Continent is modulated by the MJO, in a way that may draw some parallels and contrasts from previous studies.