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博碩士論文 etd-0912107-170519 詳細資訊
Title page for etd-0912107-170519
論文名稱
Title
南海時間序列站之生地化年間變化研究:利用一維海洋生地化模式之探討
Inter-annual variability of marine biogeochemistry at the SEATS site: application of a one-dimensional coupled physical-biogeochemical model
系所名稱
Department
畢業學年期
Year, semester
語文別
Language
學位類別
Degree
頁數
Number of pages
126
研究生
Author
指導教授
Advisor
召集委員
Convenor
口試委員
Advisory Committee
口試日期
Date of Exam
2007-07-27
繳交日期
Date of Submission
2007-09-12
關鍵字
Keywords
季風、聖嬰年、反聖嬰年、模擬、南海時間序列站、葉綠素
monsoon, La Nina, chlorophyll, El Nino, modeling, SEATS
統計
Statistics
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中文摘要
本研究利用Mellor & Yamada(1982)之一維紊流閉合模式與生地化模式偶合,發展出模擬南海上層水體生地化作用之數值模式,主要目的在探討南海北部之SEATS 測站(18oN;116oE)自1997 年初至2003 年底的生地化年間變化。由於本研究所探討之年間,曾發生兩次聖嬰(El Niño;1997∼1998 及2002∼2003)現象及兩次反聖嬰現象(La Niña;1998∼1999 及1999∼2000),因此研究的重點將放在這些事件中SEATS 測站之水文及生地化反應狀態的探討。
為瞭解此模式在物理及生地化上的表現,本研究曾針對重要的物理及生地化過程,進行理想數值實驗之模擬。物理的數值模擬顯示,對同一組模式初始場而言,風應力越大則物理模式所模擬的海表溫度與混合層深度的變化也越大,此外海水的初始垂直結構對模式模擬結果的重要性並不亞於風應力。偶合模式的數值實驗結果顯示,生地化變數初始場的計算方式與其絕對大小(硝酸鹽除外),對模式的模擬結果及其變化趨勢的影響並不大,可見此生地化初始場的計算方式還算合理。由生地化參數之敏感度數值實驗結果得知,海表層初級生產力的模擬,似乎對碎屑物質的再分解速率(δ)及浮游動物的相關參數如生長、攝食與死亡(μZ20、λ 與ε1)較為敏感,對浮游植物的集結速率(ω)則較不敏感。
海科中心之SEATS 計畫,利用SeaWiFS 衛星水色數據估算的SEATS 測站之海表面葉綠素濃度(S-chl),經由實際的船測資料進行校驗,得到從1997 年1 月∼2003 年12 月連續的S-chl。資料顯示在最近這兩個El Niño 年的冬季(12∼2 月),平均的S-chl 分別減少到低於氣候平均值達35 % 與9 %。與此S-chl 負異常值相對應的是海表溫(SST)提升,分別比氣候平均值高1.4 oC 與0.4 oC;平均風速ii
分別降低20 % 與13 %;海表面的淨熱通量也從原本的海洋損失熱量反轉成為獲得熱量或是淨熱通量趨近於0。推測此S-chl 負異常值可能為El Niño 年冬季季風減弱,降低海水的垂直混合作用,而且海水溫度分層的層化現象增強所致。本研究所發展的一維偶合物理與生地化模式可用來測試此假說。
驅動偶合模式所需要的海氣熱通量與風應力,主要是利用靠近SEATS 測站附近的NCEP 再分析資料(116.25oE; 18.095oN)計算求得。生地化變數之初始條件則是利用SEATS 計畫所取得的觀測資料。此模式成功地模擬出S-chl 與海表層總初級生產力(IPP)的季節性變化。這些結果在與實際的船測資料及SeaWiFS 衛星水色數據估算而得的資料相比對時,也呈現相當的一致性。此外,模式更成功地模擬出最近兩個El Niño 年的S-chl 與IPP 負異常值。然而,在冬季季風季強與淨熱損失增加的La Niña 年(1998∼1999 與1999∼2000 年),模式所預報相當強的S-chl 與IPP 正異常訊號並未被觀測所證實。
SEATS 測站在La Niña 年的水文資料指出,南海北部上層水中出現不尋常的高溫,且次表層之營養鹽儲量異常的低,顯示有西菲律賓海水之高鹽與低營養鹽之海水累積於南海北部,抵消掉La Niña 年增強的垂直混合作用之效應,此為一維模式所無法考慮的三維過程,可能因
而造成模式結果與實際觀測之差異。由此可知,南海北部的生地化活動在El Niño 與La Niña 年對大氣驅動力之反應相對的不對稱。
Abstract
In this study, a one-dimensional model based on the Mellor and Yamada level 2.5 turbulence closure model was coupled with a biogeochemical model to investigate the inter-annual variation of biogeochemistry at the South-East Asian Time-series Study (SEATS) Site in the northern South China Sea (SCS) from 1997 to 2003. During the study period there were two El Niño Events and two La Niña Events. This study was focused on the hydrographic and biogeochemical conditions during these events.
In order to better understand the model performance in the physical and biogeochemical aspects, numerical experiments were conducted to investigate the key processes. Numerical experiments by using idealized forcing conditions revealed that stronger wind stresses resulted in stronger cooling and deeper mixed layer. The model results were as sensitive to the initial density structure of the water column as to wind stress. Numerical experiments with the coupled model revealed that the biogeochemical results are insensitive to the initial biogeochemical conditions except the nitrate profile. Sensitivity tests indicated that primary production was sensitive to the remineralization rate constant for the detritus and parameters related to zooplankton, such as growth rate, grazing constant and mortality rate constant. It is less sensitive to iv aggregation constant of phytoplankton.
The SEATS project of the National Center for Ocean Research provided data of sea surface chlorophyll-a (S-chl) concentrations, which were derived from SeaWiFS data for the period from Jan. 1997 to Dec. 2003 by calibrating against shipboard observations. The time-series showed decreases of mean S-chl by 35% and 9% below the climatological mean in the winter months (DJF) of the two El Niño Events. The negative S-chl anomalies corresponded to elevated sea surface temperature (SST) by 1.4oC and 0.4oC above the climatological mean, while the mean wind speed (WS) was reduced by 20% and 13%, and the surface heat exchange reverted from net loss to net gain or null. It is hypothesized that the anomalously low S-chl may have been caused by the weakened wind mixing and strengthened stratification. A 1-dimensional coupled physical-biogeochemical model was developed to test this hypothesis. The model driven by wind stress and surface heat fluxes successfully reproduced the seasonal cycles of S-chl and integrated primary productivity (IPP) as compared to shipboard observations and SeaWiFS data derived values, and predicted the negative anomalies of S-chl and IPP under the 1997-98 and 2002-03 El Niño conditions. However, the model-predicted strong positive anomalies of S-chl and IPP under the 1998-99 and 1999-2000 La Niña conditions, which brought v stronger wind and heat loss, were not substantiated by observations. Hydrographic conditions at the SEATS station indicated that, under La Niña conditions, unusual accumulation of warm and nutrient-depleted water occurred in the upper water column cancelled out the effect of stronger mixing. Therefore, the biogeochemical responses of the northern SCS to surface forcing during the recent El Niño/La Niña conditions displayed in a highly asymmetrical manner.
目次 Table of Contents
致謝 i
摘要 i
Abstract iii
表目錄 ix
圖目錄 X
第一章 緒論 1
1.1 南海的環境背景 1
1.2 南海的生地化研究 3
1.3 研究動機與目的 4
第二章 研究方法與資料來源 6
2.1 模式描述 6
2.1.1 物理模式 6
2.1.2 生地化模式 8
2.1.3一維海洋物理與生地化模式之耦合 11
2.2 資料處理 12
2.2.1 熱通量與動量通量的計算 12
2.2.2初級生產力的估算方式 14
2.3資料來源 15
第三章 研究結果 17
3.1 一維海洋物理模式的理想數值實驗 17
3.1.1評估海洋表面風應力影響的理想數值實驗 17
3.1.2 評估混合層深度影響的理想數值實驗 19
3.2 一維海洋物理與生地化偶合模式的理想數值實驗 20
3.2.1 P、Z、D與chl初始場設定的敏感度數值實驗 21
3.2.2偶合模式的生地化參數之敏感度數值實驗 22
3.3 SEATS測站的多年數值實驗模擬 25
3.3.1 初始場的設計及模式驅動力(上邊界層)的給定 25
3.3.2 實驗設計 26
3.3.3 數值實驗的模擬結果 27
3.3.3.1 模式模擬變數之垂直深度剖面的連續時間變化 27
3.3.3.2 模式模擬變數在海洋表層的時間變化 28
3.3.3.3模式模擬生地化變數之垂直深度剖面比較 29
3.3.3.4模擬結果與觀測值之相關性比較 31
3.4 小結 31
第四章 討論 34
4.1 年間變化(interannual variability) 34
4.1.1 El Niño事件 35
4.1.2 La Niña事件 36
4.2 可能的影響因子 36
4.2.1 平流效應的探討 36
4.2.2 敏感度實驗 37
4.2.3 雲的遮蔽效應 39
4.3 熱通量與動量通量對模式模擬的影響與探討 40
第五章 結論 43
參考文獻 45
附錄一、生地化模式採用的參數值(Liu et al., 2002; 2007) 86
附錄二、Paper submitted to Geophysical Research Letters 87
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