新的潮汐型態指標

Abstract

本文主利用K-means法將一個新的潮型指標(PR)分成三類，當PR值小於等於0.55為半日潮型，在0.55至0.80為混合潮型，大於等於0.80為全日潮型。檢驗台灣十個潮汐測站的PR指標值不受年份的影響，大多數測站在不同年的PR值，相對標準偏差都在2%以下，其中淡水和蘭嶼因在2006年資料缺漏率達52%及31%而造成相對偏差到6%和3%，而成功地區也有6%相對標準偏差。由一季或半年的資料長度影響PR值的檢驗發現蘭嶼、成功、基隆及高雄四站一季資料長度所得PR值會超越過潮型指標界線，造成判斷成不同潮型的困難，而且發現各測站因為資料長度因素，在混合潮型和全日潮型測站的PR值的變異較在半日潮型處大，在半日潮測站PR值的最大相對標準偏差可達4%，在混合潮測站的PR值的最大相對標準偏差則為14%。 另外，本文再以潮汐的潮差及週期的常態分布機率密度函數的兩參數比值TR及TP，劃分潮型界線。當TR的判別界線為小於0.15的為半日潮，大於0.30的為混合潮，介於之間為全日潮；TP值界線為小於0.23為半日潮，大於0.29為混合潮，介於之間為全日潮，其分類群集結果與PR值分類群集結果相同。

This paper presents a new definition of tide type, period ratio (PR), to indicate three tide types using K-means method. That PR is lower than 0.55 shows semidiurnal tide and that PR exceeds 0.80 indicates diurnal tide. PR between 0.55 and 0.80 shows mixed tide. Relative standard deviation (STD) of PR within a range of 2% slightly varies for three annual tidal data sets at one of seven locations around Taiwan. However Due to a mount of data missing in 2006 Danshui and Lanyu the relative STD reach 6% and 3%, respectively. The PR at Chengkung reach 6% for annual variation of tides. Different seasonal and semiannual data lengths are examined for the variation of PR. The result shows that the PRs at Lanyu, Chengkung, Keelung and Kaohsiung vary too much to show the same tide type. PRs for different data length of diurnal and mixed tides have larger variation than those of semidiurnal tide. Maximum STD of PRs of semidiurnal tide is 4% and that of mixed tide is 14% . Other two indicators (TP and TR) for tide types are obtained from two parameters of normal distribution fitting for the tidal ranges and the periods of individual tide Lower and upper indexes of TR separating semidiurnal, mixed and diurnal tides are 0.15 and 0.30. Lower and upper indexes of TP separating semidiurnal, mixed and diurnal tides are 0.23 and 0.29.