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.

Multi-Scale Convective Systems during the Initial Phase of the 1986/87 El Niño

“…WWBs dominated the regions on and to the west of the convective system and moved eastward as the convective system moved eastward. in which the SCC propagated in the western Pacific (Nakazawa, 1988). The active convective regions (shaded in the figure) are determined threehourly, based on the GMS equivalent black body temperature index.…”

“…Also, we will present additional analyses with respect to propagating features of convective systems such as SCC, twin cyclone and WWB from the Indian Ocean through the Pacific Ocean. Here, SCC is defined as an ensemble of could clusters with a longitudinal scale of 10 to 20 degrees and a life time of about 10 days, observed near the equator (Nakazawa, 1988). A twin cyclone corresponds to cyclone pairs developed both in the equatorial northern and southern hemispheres symmetric to the equator (Keen, 1982;Nitta, 1989).…”

Equatorial Atmosphere Radar (EAR): System description and first results

“…The mechanisms responsible for these atmospheric changes and fluctuations, however, have not yet been clearly identified because of the sparseness of observational data from that region. The mechanisms that cause atmospheric changes in the equatorial region are thought to have a hierarchical (or multiple) structure, one that would require observations of the atmosphere at different horizontal scales for comprehensive description [Nakazawa, 1988]. Ideally, it is necessary to conduct coordinated experiments that include various groundbased and space-based instruments to derive a comprehensive understanding of these mechanisms.…”

A multiscale model for tropical intraseasonal oscillations

“…In mid-latitudes, the theory of baroclinic instability successfully describes the influence of coherent synoptic scales disturbances on the planetary scales. In the tropics, superclusters (2,(18)(19)(20) are the documented coherent structures on the equatorial synoptic scales [O (1,500 km)], and the observations also indicate that the MJO is a propagating planetary-scale envelope of such superclusters (2). Here we develop a multiscale model that focuses on the planetary-scale circulation anomalies induced by the interaction with equatorial synoptic-scale circulations created by a wave train of superclusters.…”