Multiscale Aspects of Convective Systems Associated with an Intraseasonal Oscillation over the Indonesian Maritime Continent

Abstract

Multiscale aspects of convective systems over the Indonesian Maritime Continent in the convectively active phase of an intraseasonal oscillation (ISO) during November 2002 are studied using Geostationary Meteorological Satellite infrared data and ground-based observational data from X-band rain radar, equatorial atmosphere radar, L-band boundary layer radar, and upper-air soundings at Koto Tabang (KT; 0.20°S, 100.32°E; 865 m above mean sea level), West Sumatera, Indonesia. In the analysis period, four super cloud clusters (SCCs; horizontal scale of 2000?4000 km), associated with an ISO, are seen to propagate eastward from the eastern Indian Ocean to the Indonesian Maritime Continent. The SCCs are recognized as envelopes of convection, composed of meso-α-scale cloud clusters (MαCCs; horizontal scale of 500?1000 km) propagating westward. When SCCs reach the Indonesian Maritime Continent, the envelopes disappear but MαCCs are clearly observed. Over Sumatera, the evolution and structure of a distinct MαCC is closely related to the organization of localized cloud systems with a diurnal cycle. The cloud systems are characterized by westward-propagating meso-?-scale cloud clusters (M?CCs; horizontal scale of ?100 km) developed in eastern Sumatera, and an orographic cloud system formed over a mountain range in western Sumatera. Ground-based observations further revealed the internal structure of the orographic cloud system around KT. A meso-?-scale convective precipitation system with eastward propagation (E-M?CP; horizontal scale of ?40 km) is found with the formation of the orographic cloud system. This is associated with a low-level wind change from easterly to westerly, considered to be local circulation over the mountain range. The E-M?CP also indicates a multicell structure composed of several meso-?-scale convective precipitation systems (horizontal scale of <10 km) with multiple evolution stages (formation, development, and dissipation).