Statistical Properties of Cloud Propagation over Sumatra during CPEA-I

Cloud propagation over Sumatra and the surrounding area (10°S-10°N, 70°-120°E) during the Coupling Processes in the Equatorial Atmosphere-I (CPEA-I) campaign (10 April to 9 May 2004) was tracked using brightness temperature (Tb) data from the GOES-9 satellite. The cloud tracking was based on three-dimensional data with a threshold of Tb 210 K. During the campaign, westward-moving clouds were more dominant than eastward-moving systems, with a ratio of approximately 4:1. This characteristic coincided with the dominant easterly wind aloft. Most clouds propagated with a speed varying between 4 and 35 m/s, with a mean value of 13.7 m/s. If the westward and eastward propagations were separated, the average duration, speed, and span of the westward (eastward) moving clouds are 7.7 (5.8 h), -14.5 (9.8 m/s), and 435.5 (187.1 km), respectively. The characteristics of cloud propagation during the CPEA-I were influenced by environmental factors such as relative humidity, temperature, the vertical movement of air, and wind shear. Suchfactors interacted with the inactive and active phases of the Madden-Julian Oscillation.