Dual Doppler Radar Observation of a Tropical Rainband Developed from Two Convective Clouds

Abstract

The structure and evolution of a small, isolated convective rainband, which developed over the warm pool between January 5 and 6, 1993, were examined in detail using sounding and dual-Doppler radar data from Manus Island, Papua New Guinea, during the TOGA-COARE TOP. The rainband developed from two small convective cells and decayed within the dual-Doppler radar coverage area.The rainband was oriented parallel to the low-level environmental shear with a lower magnitude of 2.5 x 10-3 s-1 and the CAPE was as small as 342 J kg-1. It moved from 320 to 140 at a speed of 5.5 m s-l. During its mature stage, it was 30 km long and 15 km wide. Rain water within the rainband was mainly concentrated below the 3.0 km level and decreased rapidly with height. The maximum updraft was about 4N5 m s-1 and the maximum radar reflectivity was about 3540 dBZ.The number of convective cells changed with time as follows: two at the initial stage, five at the developing stage, and one at the mature stage. The low-level front inflow was lifted upward within the cells, formed the main updrafts over the reflectivity cores, and then moved toward the trailing region. There were no strong downdrafts below the heavy rainfall area, and there was no widespread stratiform region behind the convective region. Convective-scale rear inflows were observed in the early stage. These rear inflows aggregated with each other, increased in area and depth, and developed into a flow like a gravity current. The aggregated rear inflow with a gravity current "head" moved faster than the rainband, caused strong low-level convergence, and triggered explosive development of a convective cell in the mature stage, according to a detailed analysis of the dual Doppler radar data. The aggregation of convective-scale rear inflows appears to be important in the organization of a rainband.

Multiscale Organization of Convection Simulated with Explicit Cloud Processes on an Aquaplanet

“…Cloud clusters are a common tropical cloud system (Leary and Houze 1979;Houze and Betts 1981;Takayabu and Murakami 1991;Mori 1992Mori , 1995Satoh et al 1995;Chen et al 1996;Houze et al 2000). Studies using data from the Global Atmospheric Research Program's (GARP) Atlantic Tropical Experiment (GATE) showed that a CC is comprised of cloud systems organized on the mesoscale with a horizontal scale of O(10 km) and a lifetime of several to ten hours (e.g., Zipser 1969Zipser , 1977Houze 1977; Leary and Houze 1979;Zipser et al 1981;Mori 1992Mori , 1995Satoh et al 1995;Fujiyoshi and Geng 1995;Takahashi and Uyeda 1995;Chen et al 1996;Houze et al 2000). A variety of terms have been used to define various mesoscale cloud systems, such as mesoscale precipitating feature (MPF; Leary and Houze 1979), mesoscale convective system (MCS; Houze 1993, p. 334), rainband, squall line, and sometimes cloud cluster.…”

Doppler Radar Observations on the Structure and Characteristics of Tropical Clouds during the TOGA-COARE IOP in Manus, Papua New Guinea

“…The 5J (5 January) case is that of an echo merging, evolved under a relatively stable condition by taking a long time (about three hours) for a small echo to reach to the maximum echo area (810km2). Fujiyoshi and Geng (1995) described the development process of this echo. The 16D(a) (First line echo of 16 December) and 16D(b) (Second line echo of 16 December) are squall-line-like echoes developed successively in the southeast and northwest of Manus.…”

“…The role of the warm-rain process in squall lines at Darwin, Australia, was discussed by Keenan and Rutledge (1993). As an example of a simple case of cloud development, Fujiyoshi and Geng (1995) analyzed an isolated convective echo over the sea (5 January case) and described the process and mechanism of the merging effect of clouds for development in a relatively stable condition. At the beginning stage of the cloud cluster development, the warm-rain process dominated.…”

Tentative Utilization of a Raindrop Size Distribution Meter Specially Designed for the Observation of Tropical Precipitation in the TOGA/COARE Project

“…7b. Fujiyoshi et al (1994) had supposed that such enhancements of echo intensity were caused by coalescence growth taking place, namely, the "warm-rain mechanism". The results of the present work show simultaneous measurements of an increase in frequencies around 1.0mm in diameter on the size distribution of raindrops in Fig.…”