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Advances in Meteorology
Volume 2017 (2017), Article ID 5962356, 15 pages
https://doi.org/10.1155/2017/5962356
Research Article

Early Detection of Baby-Rain-Cell Aloft in a Severe Storm and Risk Projection for Urban Flash Flood

1Disaster Prevention Research Institute, Kyoto University, Uji, Kyoto 611-0011, Japan
2Graduate School of Engineering, Kyoto University, Uji, Kyoto 611-0011, Japan
3Sumitomo Heavy Industries, Ltd., Shinagawa, Tokyo 141-6025, Japan
4Tokyo Electric Power Company Holdings, Inc., Chiyoda, Tokyo 100-8560, Japan

Correspondence should be addressed to Eiichi Nakakita; pj.ca.u-otoyk.irpd.dmh@atikakan

Received 22 July 2016; Revised 10 November 2016; Accepted 15 December 2016; Published 22 January 2017

Academic Editor: Ke Zhang

Copyright © 2017 Eiichi Nakakita et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

In July 2008, five people were killed by a tragic flash flood caused by a local torrential heavy rainfall in a short time in Toga River. From this tragic accident, we realized that a system which can detect hazardous rain-cells in the earlier stage is strongly needed and would provide an additional 5 to 10 min for evacuation. By analyzing this event, we verified that a first radar echo aloft, by volume scan observation, is a practical and important sign for early warning of flash flood, and we named a first echo as a “baby-rain-cell” of Guerrilla-heavy rainfall. Also, we found a vertical vorticity criterion for identifying hazardous rain-cells and developed a heavy rainfall prediction system that has the important feature of not missing any hazardous rain-cell. Being able to detect heavy rainfall by 23.6 min on average before it reaches the ground, this system is implemented in XRAIN in the Kinki area. Additionally, to resolve the relationship between baby-rain-cell growth and vorticity behavior, we carried out an analysis of vorticity inside baby-rain-cells and verified that a pair of positive and negative vertical vortex tubes as well as an updraft between them existed in a rain-cell in the early stage.