マルチパラメータ・フェーズドアレイ気象レーダーを用いたダウンバーストを発生させる積乱雲の力学的構造の解析

Abstract

Dynamical structure and mechanism of a downburst-producing cumulonimbus cloud system in Tokyo on August 27, 2018, is examined using a state-of-the-art multi parameter phased-array weather radar. Before the outbreak the downburst, three characteristics that are considered to be precursors of the downburst were observed in the cumulonimbus cloud; (1) a precipitation core descended from above 5 km toward the ground surface 4 min before the outbreak, (2) a reflectivity notch deepened at 4–5 km, and (3) a strong horizontal convergence appeared at 3–4 km. Corresponding to these precursor regions, there are vortex pairs with positive and negative vertical vorticity, respectively, and the downdraft was distributed across the vortex pairs. These results suggest that the horizontal vortices of the background wind may have been raised by the downdrafts in the cumulonimbus cloud to form vertical vortex pairs and contribute to the generation of the downburst.