台灣沿岸氣象海嘯特性之初步研究

Abstract

本文利用所收集台灣沿岸12測站，自2008年1月至2009年7月間之潮位資料，以FFT、Wavelet與EEMD分析氣象海嘯現象發生之時段。且探討氣象海嘯發生之時間與空間分布特性、週期分布特性，及海嘯週期與港灣共振週期之關係。本研究結果發現台灣氣候海嘯發生之時間集中在1-3月間，發生地點以北台灣為主，發生之最大振幅達到1.0-1.5公尺，相對年平均潮差之比值約有0.4-0.6。在週期分布特性上，除了海嘯週期(10-60分鐘)區間外，相同的外力因素也會附帶1-10分鐘週期之訊號。本研究發現各港灣內大部份氣象海嘯現象並無受到港池共振之影響，因此觀測到氣象海嘯現象之水位變化多低於1公尺。最後本研究分析壓力變化與氣象海嘯之相關性時發現，必須使用高取樣頻率之訊號，方能分析出氣象海嘯之變化特性；而使用方均根分析氣象海嘯特性的平均時間建議以30-40分鐘為佳。另外本研究發現在季節風影響下，陣風風速大幅度跳動也是影響氣象海嘯振幅的因子之一。

This paper investigates meteo-tsunami around Taiwan through FFT, Wavelet and EEMD methods based on collected tide data during Jan, 2008 to July, 2009 at 12 tide stations. The temporal and spatial distributions, and the dominant periods of meteo-tsunami around Taiwan was discussed and related to harbor resonance. Meteo-tsunami more occasionally happens in the period of from January to March and at the north waters of Taiwan than the other months and waters due to northeastern monsoons. The maximum amplitude of meteo-tsunami can reach 1.0-1.5 m, whose relative amplitude to mean tidal range is about 0.4-0.6 m. Meteo-tsunami with periods less than 10 minute was newly found together with possibly existing components, which were identified by the previous researchers, with periods ranged from 10-60 minute. Most dominant periods of meteo-tsunami are off from the modes of harbor resonance so that meteo-tsunamis are not amplified in the harbors and are less than 1m. The relationship between pressure variation and meteo-tsunami was confirmed from data at high sampling rate. The characteristics of meteo-tsunami can be clarified by taking root mean square on data at a mean of about 30-40 minute. An interesting speculation is that l:arge jump of the gust during monsoon is a possible factor generating meteo-tsunami.