Intraseasonal variation of raindrop size distribution at Koto Tabang, West Sumatra, Indonesia

Intraseasonal variation of raindrop size distribution (DSD) in response to Madden Julian Oscillation (MJO) is studied using a 2D video disdrometer (2DVD), a boundary layer radar (BLR) and the Equatorial Atmosphere Radar, operated at Koto Tabang, west Sumatra, as well as GOES-9 infra-red brightness temperature. As a parameter of DSD, Delta Z(MP), which is defined as the difference between a measured radar reflectivity in dB and that from the Marshall-Palmer (MP) radar reflectivity (Z) - rain rate (R) relationship, Z = 200 R-1.6, is used. It is found that in non-active phase of MJO, 2DVD-derived Delta Z(MP)s are generally positive, indicating that DSDs are broad, while they decrease toward negative values as the phase of MJO shifts to active ones. Rain-top height derived from the BLR indicates that the convective processes are more intense in the non-active MJO phase than in the active phase, which would cause the difference in DSDs.