1924年6月22日社頭龍捲風事件的氣象特徵與救災應變

Meteorological Characteristics and Disaster Responses to the Shetou Tornado Event on June 22 of 1924

龍捲風為短時間發生的劇烈氣流旋渦現象，可導致天氣災害。龍捲風的生命期通常不逾10分鐘，總移動距離數公里。本研究分析1924年6月22日上午9時53分的彰化員林-社頭陸龍捲，該龍捲風發生於員林驛南方3哩5鎖（4.93公里）1、社頭驛北方1哩（1.61公里），旋轉空氣柱持續約10分鐘，影響區域110-130平方公尺，以致自臺南發車北上的第28號列車翻覆。就公共安全與傷亡規模皆具代表性，其為日治時期文獻首次記錄列車遭旋風吹襲，並引起官方關切，《臺灣總督府（官）報》〈彙報觀象〉紀錄之；日治時期龍捲風肇致的傷重程度，該個案排名第22，共45人遭害。
綜合分析天氣圖、測站數據和美國國家海洋大氣總署20世紀重分析資料，此個案的鋒面前緣有不穩定的暖濕空氣、較強的西南風、暖空氣平流、垂直風切、對流不穩定等氣象條件，加上彰化平原廣大水田的水氣供應和八卦山台地的地形抬升，皆利龍捲風的形成和發展。文史資料著重災時的境況與災後應變，地方保甲壯丁團協力救災，以及列車調度與修復顯示日治時期已有城鄉連結的緊急救援機制。

A tornado is a type of violent vortex that occurs over a short period and can cause severe weather disasters. On average, the life cycle of a tornado is usually less than 10 minutes, and its total travel distance is around several kilometers. An overview of 11 tornado cases in Taiwan during the Japanese colonial period shows that sudden, intense convective events often caused human casualties and building damage. This study analyzes the land tornado that occurred between Yuanlin and Shetou, Changhua, at 9:53 a.m. on June 22, 1924. The tornado occurred at an approximate location 3 miles and 5 suoes (4.93 kilometers) south of Yuanlin Station and 1 mile (1.61 kilometers) north of Shetou Station. The rotating column of air lasted for 10 minutes and affected an area of 110-130 square meters, causing the derailment of Train No. 28 northbound from Tainan. In terms of public safety and the scale of casualties, this incident is representative. First of all, this case is the first tornado event recorded in documents from the Japanese colonial period in which a train was affected, and it gave rise to official concern. The“Comprehensive Report Weather Observation”included in Taiwan Governor's Office (Official) News recorded this incident. As far as severity of injuries, this case ranked 2nd with a grand total of 45 people having suffered from the calamity.
A comprehensive analysis of weather maps and meteorological station data from the Japanese rule period, as well as 20th-century reanalysis data from the U.S. National Oceanic and Atmospheric Administration, reveals that this case exhibited favorable meteorological conditions, including unstable warm and humid air at the pre-frontal edge, strong southwest winds, warm air advection, vertical wind shear, and convective instability. These conditions, combined with moisture from the vast paddy fields of the Changhua Plain and the topographically forced lifting effect of the Bagua Mountain Plateau, all contributed to the formation and development of the tornado. This study also uses historical documents from the Japanese rule period to reconstruct the whole event. Local Baojia youth teams joined disaster relief efforts, and the dispatch and repair of trains demonstrate an emergency relief mechanism that connected urban and rural areas during the Japanese rule period.