| 摘要: | 本研究主要受美國及荷蘭預計在2020年共同開發的海上城市計畫(Floating City Project)所啟發，此計畫目前規畫之建設預定地為中美洲外海近赤道東太平洋海域。考慮到未來海上城市的水資源問題，本研究致力於對目標區域(6N-12N,86W-94W)之濕季降水的年際變化進行分析。研究中根據目標區域在雨季的降水氣候型態，主要將雨季分為三個時期，第一時期為五、六月，第二時期為七、八月，第三時期為九、十月。透過合成分析的方法，分別對1979-2014年之間每一時期取出六個乾年及六個濕年進行合成，並利用其結果進行分析。
根據水氣收支方程(Moisture Budget)在目標區域的診斷結果顯示出，第一及第二時期在乾年的降水受減弱的上升運動及乾平流影響，在濕年的降水受增強的上升運動及濕平流影響。第三時期垂直運動變化對於降水的影響力則是不管在乾年或是濕年都較第一、第二時期來得高，反之水氣平流變化對於降水的影響程度則是第一、二時期較第三時期來的相對明顯。從全球海溫及目標區域之降水相關性的分析結果顯示，目標區域的降水與太平洋及大西洋的海溫變化均有相關性存在。所以本研究進一步使用經驗正交函數(EOF)分別對太平洋及大西洋分離出訊號強度較高的前三個海溫震盪模態，使用各模態海溫震盪訊號與目標區域降水進行相關性及多元回歸分析，可以驗證第一、第二時期的乾濕年主要受到中太平洋聖嬰(CP)、東太平洋聖嬰(EP)及北大西洋震盪(NAO)訊號所影響，到了第三時期的降水則只受到CP及EP的影響。其中CP及EP兩類聖嬰的生命週期對於沃克環流強弱的影響，以及NAO對於北大西洋副熱帶高壓強弱變化的影響即為主導著水氣垂直平流變化與水氣水平平流變化的主要原因，間接呼應了水氣收支方程對於目標區域降水變化診斷之結果。
;This research is inspired by Floating City Project which is going to be implemented by American and Netherland Cooperated Institution in 2020. The floating city has been planned to construct over the eastern equatorial Pacific Ocean near Central America in the project. Consider to the future water resource problem of the floating city, this research is dedicated to understand inter-annual precipitation variation over Target Area (6N-12N, 86W-94W) in rainy season. Target Area is actually a place where the floating city would be built in 2020. In this research, climatology rainy season of Target Area has been classified as three periods. Period-1, Period-2 and Period-3 are represent of May-June, July-August and September-October respectively. Wet years and dry years are picked up in each period, then analysis of atmospheric and oceanic gridded datasets would be conducted through composite analysis method according to these wet and dry years.
Follow the diagnostic results of moisture budget over Target Area, Period-1 and Period-2 has dry advection and downward motion anomaly contribution for less precipitation in Dry year. Conversely, wet advection and upward motion anomaly contributed for more precipitation in Wet year. With regard to Period-3, contribution intensity of vertical motion anomaly is much higher than Period-1 and Period-2, but for advection term contribution is much less than former two periods. From the results of correlation analysis between global sea surface temperatures (SST) and Target Area precipitation, precipitation has found to have related with Pacific and Atlantic SST. Therefore, this research further applied Empirical Orthogonal Function (EOF) with SST datasets to separate out the most three significant climate oscillation signals of Pacific and Atlantic Ocean. Through correlation and multi-regression analysis of climate oscillation signals and precipitation, Period-1 and Period-2 precipitation are demonstrated that affected by Central Pacific ENSO (CP), Eastern Pacific ENSO (EP) and North Atlantic Oscillation (NAO). When getting into Period-3, precipitation only affected by CP and EP in this time. Especially for Walker Circulation variation during CP and EP events, Atlantic Subtropical High variation during NAO event, these phenomenon are the main cause of vertical motion and advection anomaly contribution, it is also consistent with the diagnostic results of moisture budget. |
