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

Abstract

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, ΔZMP, 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 R1.6, is used. It is found that in non‐active phase of MJO, 2DVD‐derived ΔZMPs 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.