Statistical Properties of Stratiform and Convective Rain-rates under Seasonal Changes and MJO Propagation at Jakarta, the Maritime Continent

The Megacity Jakarta encounters hydrometeorological hazards driven by intense and/or frequent rainfall. The Madden-Julian Oscillation (MJO), a large-scale atmospheric disturbance propagating eastward through the tropics every 30–60 days, influences rainfall variability in Jakarta. Existing studies often rely on coarse-resolution data and neglect the distinct roles of stratiform versus convective rain-rates, especially in relation to the MJO. This study examines the locally diurnal and seasonal characteristics of stratiform and convective rain-rates and variations with the MJO, using high-resolution C-band Doppler radar data (2009–2012). Results show that although convective rain rates peak in Dec-Jan (DJF), the intensity calculated over rainy pixels is higher in Sep-Oct (SON). The diurnal afternoon peak of rain-rate total is primarily attributed to the convective rain-rate over mountains (24%) and lowlands, whereas the morning peak of overall rain-rate is affected by the stratiform rain-rate (11%). There is a higher proportion of stratiform rain-rate during the MJO active phase, and this rain-rate is not particularly tied to the diurnal cycle. However, in JJA and SON, the suppressed MJO phases produce a larger ratio of stratiform to convective rain-rates, with a more localized signature. The stratiform rain-rate in the suppressed phase is likely associated with anvils from the isolated convection, while in the active phase, it is linked to the large-scale MJO envelope. The high convective rain-rate during SON, despite lower overall totals, implies greater potential for flash flooding due to its intensity. Therefore, understanding the seasonal predominance of rain types by MJO phase can improve early-warning accuracy for Jakarta.