應用渦流相關法探討地表水氣通量與熱通量之特徵：以亞熱帶季節性常綠闊葉林為例;Investigating the Seasonal Variability of Surface Heat and Water Vapor Fluxes with Eddy Covariance Techniques: A Subtropical Evergreen Forest as An Example

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Title:	應用渦流相關法探討地表水氣通量與熱通量之特徵：以亞熱帶季節性常綠闊葉林為例;Investigating the Seasonal Variability of Surface Heat and Water Vapor Fluxes with Eddy Covariance Techniques: A Subtropical Evergreen Forest as An Example
Authors:	陳奕穎;Chen,Yi-ying
Contributors:	水文與海洋科學研究所
Keywords:	通量觀測;渦流相關法;資料缺補;能量閉合;地表過程;通量參數化;eddy covariance;gap-filling;energy closure;land surface process;surface parameterization;evapotranspiration;Penman-Monteith
Date:	2012-07-12
Issue Date:	2012-09-11 18:26:04 (UTC+8)
Publisher:	國立中央大學
Abstract:	地表與大氣之間水、熱通量交換速度的快慢，不但影響著近地表邊界層的發展，亦同時牽動著區域性氣候變化以及流域集水區之水文循環。為了瞭解上述的自然現象，我們常常透過數值模式對未來的環境進行模擬或預測。但是對這些模式而言，邊界條件的給定是相當重要的，例如：水文模式中的蒸發散估算、氣候模式中動量、水氣與熱通量的參數化方式。因此，惟有正確的瞭解這些通量的傳輸機制以及其在時間上的變化特性，這些模式工具才能提供給我們可靠的計算結果，讓我們瞭解地表-大氣的交互作用及其影響。在台灣應用渦流相關法觀測地表通量的技術相較於歐、美、日等國起步較晚，但近期已急起直追。且台灣本島丘陵森林居多且茂密，提供了在複雜地貌下應用渦流相關法的研究空間。本研究試圖瞭解在複雜地貌下以渦流相關法進行地表水、熱通量觀測所面臨的挑戰並提供解決方式，並將通量結果進行參數化，期有助於地表通量觀測與陸面過程之研究。本文根據文獻回顧、研究測站、研究方法、結果討論以及結論進行分段，主要可成六個章節。其中，第三章至第五章分別針對不同研究議題進行撰寫。第一章對渦流相關法的基礎理論與應用層面的文獻進行回顧。第二章則是介紹蓮華池研究樣區所架設之觀測儀器以及該測站的長期氣候狀態。第三章是說明如何在地形複雜的地貌條件下進行渦流相關法，期達到對地表水氣與熱通量進行精準的觀測。第四章則是敘述本研究所發展的一個地表水氣通量資料缺補的統計模式。第五章則發展地表阻抗的參數化模型。第六章是總結本研究之相關發現，並對地表通量觀測未來研究發展提出建議。彙整各章節的研究結果：於蓮華池測站進行渦流相關法觀測地表通量時會面臨能量不閉合的狀況；然此不閉合的狀態存在著一個明顯的季節性變化特徵，夏天能量閉合低(小於1)且較密集、而冬天較散亂能量閉合度高(大於1)。進一步使用通量源、匯模式對地表通量源、匯位置進行計算與調查。結果指出冬天的通量源位置較分散，且有部分會超出集水區的範圍；夏季通量源位置較集中，多數落於觀測塔附近。推論能量閉合度的高、低是季節性風場所造成與紊流發展強、弱有關。此外，在複雜的地形條件下以渦流相關法進行通量觀測建議採用平面擬合參考座標系統，並配合較長的平均時距，以60或120分鐘較佳，可降低短期能量閉合的不確定性，長期可達到年尺度的能量守恆。經由Ogive法分析水氣與熱通量觀測結果指出，使用較長的平均時距可以有效地觀測到紊流尺度較大的渦漩所動的可感熱通量，尤其是在午後熱對流較旺盛的期間。對於通量資料缺補模式的發展，主要結合主成分分析法與非線性內插方程式進行水氣通量資料缺補的統計模式開發，這個部分的研究結果指出：日間與夜晚應採取不同的內插樣本數，可以獲得較佳的通量資料缺補的結果。而地表參數化的研究，則是採用了Penman- Monteith方程式與實測通量結果繁衍地表阻抗。該研究資料顯示：當地表由濕變乾，地表阻抗與輻射之關聯性增加，地表阻抗與風速之關聯性減低；反之亦然。進一步嘗試將此地表阻抗特性參數化成微氣象因子與土壤水分之函數。該模式搭配標準微氣象觀測資料，可提供小時時間尺度下水氣通量或蒸發散量的推估。即當植被層上的微氣象條件與植被層下的土壤水分狀態同時取得時，地表水氣通量即可以Penman-Monteith方程式進行合理推算。目前成果多為針對環境條件與地表水氣或熱通量傳輸速率之影響進行探討，植物生生理反應對地表通量傳輸之機制調查仍顯不足。未來應可對碳通量進行觀測，進行植物生理對地表水、熱通量傳輸機制與特徵之探討。his dissertation focused on using eddy covariance technique to investigate a variety of primary hydrologic, radiative and turbulent transport processes driving forest-atmosphere exchanges of heat and water vapor at a subtropical evergreen forest. A total of six chapters was described in this study. A brief literature review on theoretical and applied eddy covariance techniques was introduced in Chapter1. Climatological condition and experimental setup at Lien-Hua-Chih study site were presented in Chapter 2. Determining the adequate averaging periods and reference coordinates for measuring surface heat and water vapor fluxes over the mountainous terrain was devoted in Chapter 3. In sequent Chapter 4, a gap-filling model, combining principle component analysis and the K-nearest neighbor algorithm, for estimating latent heat gaps was developed. In Chapter 5, a surface resistance parameterizing model for the Penman-Monteith equation suitable for application on hourly time scale was proposed. Finally, some thoughts summarizing my findings and future works were given in Chapter 6.To summarize, the seasonal energy closure variation at this study site was concluded as the result from having weak turbulence developments during wet seasons and mismatching flux footprint areas among flux sensors during dry seasons. The Ogive function analysis revealed that the energy closure was improved with the increase of averaging time by capturing sensible heat fluxes at low-frequency ranges during certain midday hours. For planar-fit rotation approach, a typical averaging period (30 min) is not suitable and a 60 min or 120 min averaging period is an adequate averaging period for calculating eddy fluxes at this study site. The developed gap-filling approach by incorporating the adaptive interpolation method resolves the eddy covariance data gaps problem on various timescales ranging from hours to years. Using an integrated hydrometeorological flux tower and field experiments, the surface resistance can be reasonably parameterized as a function of radiation forcing and environmental factors if meteorological conditions above canopy and soil moisture contents are well known.For my future work, this framework can be broadened to investigate the carbon exchange, e.g., CO2 flux, between terrestrial ecosystem and atmosphere for better understanding the effect of biological controls on evapotranspiration.
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