Tropical Super Clusters within Intraseasonal Variations over the Western Pacific

Abstract

The fine structure of super clusters was analyzed using the 3-hourly Geostationary Meteorological Satellite (GMS) Infrared (IR) data. A super cluster is defined as an ensemble of cloud clusters having different life stages with an observed horizontal scale of several thousand kilometers found near the equator during the active phase of intraseasonal variations (ISVs). Super clusters move eastward with a phase speed of about 10-15ms-1. GMS IR data reveal that the life time of each cloud cluster within a super cluster is about 1-2 days and its phase propagation is westward along the equator. Although each cloud cluster moves westward, a super cluster moves eastward due to the successive formation of a new cloud cluster east of the mature-stage cloud cluster. The above results suggest the existence of a hierarchy of convective activity in the tropical atmosphere.
During the onset phase of the 1986/87 ENSO event in November 1986, an eastward moving super cluster was observed over the western Pacific to the dateline.