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

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  • Fujiyoshi Yasushi
    Institute for Hydrospheric-Atmospheric Sciences, Nagoya University
  • Geng Biao
    Institute for Hydrospheric-Atmospheric Sciences, Nagoya University

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Other Title
  • 熱帯域で二つの対流性エコーから発達したレインバンドのデュアルドップラーレーダー観測
  • 熱帯域で2つの対流性エコーから発達したレインバンドのデュアルドップラーレーダー観測〔英文〕
  • ネッタイイキ デ 2ツ ノ タイリュウセイ エコー カラ ハッタツシタ レイン

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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 IOP. The rainband developed from two small convective cells and decayed within the dual-Doppler radar coverage area.<br>The rainband was oriented parallel to the low-level environmental shear with a lower magnitude of 2.5×10-3 s-1 and the CAPE was as small as 342 J kg-1. It moved from 320° to 140° at a speed of 5.5m s-1. During its mature stage, it was 30km long and 15km wide. Rain water within the rainband was mainly concentrated below the 3.0km level and decreased rapidly with height. The maximum updraft was about 4∼5m s-1 and the maximum radar reflectivity was about 35∼40 dBZ.<br>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.

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