Raindrop size distributions of convective rain over equatorial Indonesia during the first CPEA campaign

Abstract

As part of the Coupling Processes in the Equatorial Atmosphere (CPEA) campaign, precipitation was observed at Kototabang (0.20°S, 100.32°E), Indonesia, by a 2D-Video Disdrometer (2DVD), a 1.3-GHz wind profiler, an Equatorial Atmosphere Radar (EAR) and a Mobile Automatic Weather Station (MAWS). The campaign period is from April 10 to May 9, 2004. This paper presents a comprehensive follow-up of the previous study on the intraseasonal variation (ISV) of raindrop size distribution (DSD) during this campaign. The data were partitioned into stratiform, mixed stratiform/convective, deep convective and shallow convective. Besides the DSD parameters of gamma distribution, Δ Z MP defined as the difference between a measured radar reflectivity and that from Marshall and Palmer's model was also analyzed. Intraseasonal variation of Δ Z MP was only found at heavy rain. Consistent with the previous study, during the inactive phase, Δ Z MP s were generally positive (broad DSD) and decrease toward negative values (narrow DSD) as the phase of ISV shifts to active ones. We found that a broad DSD and skewed towards higher drop diameters during the inactive ISV phase came mainly from deep convective, while a narrow DSD during the active phase came mainly from shallow convective events. Like surface DSD, mass-weighted mean diameter ( D m ) revealed from the EAR measurement was also larger during the inactive phase (deep convective) than that for the active phase (shallow convective). In general, we found that vertical profile of reflectivity gradient (VPRG) from 1.3-GHz wind profiler observations during the inactive phase was larger than for the active phase. This phenomenon may be due to significant coalescence process during the inactive phase.