Case study on internal structure of westward migratory cloud systems with diurnal cycle observed in the west Sumatera during HARIMAU2006 campaign

A diurnal cycle of systematic migration of cloud systems exists over the entire Sumatera Island (about 1,500 km in length) in Indonesia. The cloud systems develop in a mountainous area in the afternoon and migrate westward and/or eastward for several hundred kilometers (about 500 km) from night to morning. Three-dimensional distribution of precipitation in the western part of Sumatera Island was obtained by Hydrometeorological ARray for ISV-Monsoon AUtomonitoring (HARIMAU) 2006 campaign. The internal structure and its process of the migratory cloud systems with diurnal cycle observed on 10 November 2006 were investigated by dual-Doppler radar analysis in order to understand the mechanisms of the diurnal cycle. Convection got active in the mountainous area around 11 LST, organized precipitation systems with a horizontal scale of several tens of kilometers migrated westward. The precipitation systems developed again over the sea off the western coast of Sumatera Island and became bigger than those over the land. The horizontal scale of the precipitation systems was 100 km in long axis which was on a parallel with the west coast line of Sumatera Island. Internal structure of the precipitation systems consisted of convective area which developed up to 16 km in height in the leading edge of the precipitation systems and stratiform area with a horizontal scale of 20 km in the rear of the leading edge. Downdraft was observed below 2 km in the leading edge of the precipitation systems. A storm-relative inflow turned to updraft above a gust front derived from the downdraft. It is considered that the inflow played an important role in the maintenance of the precipitation systems as a water vapor supply to the precipitation systems.