| 摘要: | 近年來，全球暖化導致北極海冰迅速融化，增加了流入北大西洋的淡水，進而加強海洋分層。大氣和海洋之間的熱平衡交互作用影響了大西洋深層水（North Atlantic Deep Water, NADW）的形成。位於北極的弗拉姆海峽是一個關鍵點，它是北極海冰流向北大西洋的主要通道，其中的西斯匹次卑爾根洋流（West Spitsbergen Current, WSC）是向北極海輸送熱量和鹽分的主要途徑。這個海流的特徵以及由西北轉西南迴流至北大西洋的循環過程對北極海冰迅速消退和NADW的形成至關重要。特別是，海洋渦漩可能是推動這一循環過程的關鍵因素。此外，弗拉姆海峽也是北極海邊緣冰區的重要部分。隨著海冰年輕化和變薄，它更易受波浪能量破壞。這不僅影響北極海冰的厚度和面積，也增加了波浪模式預測的挑戰，迫切需要對波浪與海冰交互作用進行更精確的參數化。
本研究專注於弗拉姆海峽邊緣冰區的波浪特性和WSC的變異性，旨在定量分析波浪與海冰的交互作用及探討WSC變動對NADW生成的影響。本研究利用國立中央大學自製的微型波浪浮標，於2021至2023年的夏末秋季（8月至10月），在弗拉姆海峽，位於北緯77.5至78.5度、東經6至13度範圍內的海域，以陣列形式進行實地觀測。實驗期間共佈放36顆浮標，量測示性波高、波浪周期、波浪能譜、海表粗糙度和海表溫度（Sea Surface Temperature, SST）等海洋參數，以量化受邊緣冰區海冰影響的波浪能譜衰減率。此外，我們將觀測數據與北極波浪數值模式數據集Arctic Ocean Wave Analysis and Forecast （AOWAF）與ECMWF Reanalysis v5（ERA5）波浪場進行比較，以多種統計指標定量評估模式的表現。同時，我們使用水平擴散係數、有限尺度Lyapunov指數（Finite-Size Lyapunov Exponents, FSLE）、渦漩辨識和海表溫指數衰減時間等分析手段，研究浮標軌跡和海表溫度觀測數據，探討WSC的海表動力、渦漩活動和海氣熱交換的時空分布特徵對NADW生成的影響。為了增加資料的樣本量，本研究還包括了OSMC（Observing System Monitoring Center）的漂流浮標軌跡數據，將其作為分析的額外數據來源。
本研究在弗拉姆海峽進行的波浪特性研究顯示，弗拉姆海峽九月的示性波高與海冰邊界位置存在正相關。當波浪模式納入波冰交互作用後，對波浪週期的估算更為準確。比較統計結果顯示，AOWAF和ERA5均低估了示性波高，其百分比誤差分別為13.02%和8.31%。在R2方面，兩者均接近0.9。然而，兩模式在平均週期的趨勢出現了歧異：AOWAF模式的估計僅低估5.36%，而ERA5則高估了36.6%，顯示AOWAF在考慮波冰交互作用方面具有優勢，這與波浪週期取決於波浪譜型有關。譜寬參數與波齡倒數分析結果顯示，受海冰影響的弗拉姆海峽高頻波浪譜寬較窄。基於對冰中波浪的實地觀測，發現海冰區的波浪能量衰減率隨週期的降低而增加，遵循??(??)=??*??-4.51的衰減形式。
在WSC變異性分析結果中，本研究發現WSC在耶爾馬克高原（Yermak Plateau, YP）西南區域和莫洛伊深淵(Molloy Deep, MD)東側出現流向分岔和相對WSC主流較強的中尺度海水混合（Richardson擴散）。這個分岔點同時也是SST指數衰減時間場的梯度增大、海洋熱量大量散失到大氣（?120 W/m2）的區域。我們透過擴散係數場進一步發現，WSC在MD西側與HG區域等先前文獻指出的迴流區，出現海表水匯聚而形成沉降力的現象，這些迴流區主要由反氣旋式渦旋（佔94.44%）主導，這對當地的海洋垂直運動產生了影響。此外，風場條件被發現是有利於迴流區反氣旋式渦旋形成的關鍵因素之一。
;In recent years, global warming has led to rapid melting of Arctic sea ice, increasing the influx of freshwater into the North Atlantic and thereby intensifying ocean stratification. The heat balance interaction between the atmosphere and ocean has been influencing the formation of North Atlantic Deep Water (NADW). The Fram Strait, located in the Arctic, is a critical point as the main channel through which Arctic sea ice flows into the North Atlantic. The West Spitsbergen Current (WSC) within this strait is the primary pathway for transporting heat and salinity to the Arctic Ocean. The characteristics of this current and its circulatory process, transitioning from northwest to southwest into the North Atlantic, are crucial for the rapid retreat of Arctic sea ice and the formation of NADW. Particularly, oceanic eddies may play a key role in driving this circulation. Furthermore, the Fram Strait constitutes a significant part of the Arctic′s marginal ice zone. With sea ice becoming younger and thinner, it is increasingly susceptible to wave energy, affecting the thickness and extent of the Arctic sea ice and posing challenges to wave model predictions. This underscores the urgent need for more accurate parameterization in modeling wave-ice interactions.
This study focuses on the wave characteristics in the marginal ice zone of the Fram Strait and the variability of the WSC, aiming to quantitatively analyze the interactions between waves and sea ice and investigate the impact of WSC variations on the formation of NADW. Utilizing micro-wave buoys developed by National Central University, field observations were conducted in an array format within the Fram Strait (77.5°N to 78.5°N, 6°E to 13°E) during the late summer and autumn seasons (August to October) from 2021 to 2023. A total of 36 buoys were deployed to measure significant wave height, wave period, wave spectrum, sea surface roughness, and temperature (SST), quantifying the attenuation rate of the wave spectrum affected by sea ice in the marginal ice zone. Observational data were compared with the Arctic Ocean Wave Analysis and Forecast (AOWAF) and ECMWF Reanalysis v5 (ERA5) wave fields, using various statistical metrics to assess model performance. Additionally, horizontal dispersion coefficients, Finite-Size Lyapunov Exponents (FSLE), eddy detection, and SST e-folding time were employed to study buoy trajectories and SST data, exploring the spatial and temporal distribution of WSC surface dynamics, eddy activity, and air-sea heat exchange and their impact on NADW formation. To augment the data sample size, this study also incorporated drifting buoy trajectory data from the Observing System Monitoring Center (OSMC) as an additional source for analysis.
Our study in the Fram Strait shows a positive correlation between significant wave height in September and the position of the ice edge. Including wave-ice interactions in wave models led to more accurate estimations of wave periods. Statistical comparisons reveal that both AOWAF and ERA5 models underestimated significant wave heights, with percentage errors of 13.02% and 8.31%, respectively, while both achieving R2 values close to 0.9. However, the models diverged in estimating average periods: AOWAF underestimated by only 5.36%, whereas ERA5 overestimated by 36.6%, indicating AOWAF′s superiority in accounting for wave-ice interactions, linked to wave period dependency on wave spectral shape. Spectral width parameters inversely correlated with wave age demonstrate narrower spectra for high-frequency waves in the ice-affected Fram Strait. Field observations of waves within ice reveal an increase in wave energy attenuation rates with decreasing periods, following an ??(??)=??*??-4.51 decay pattern.
In the variability analysis of WSC, the study found bifurcations and mesoscale sea water mixing (Richardson dispersion) near Yermak Plateau (YP) and Molloy Deep (MD), coinciding with increased SST index decay time gradients and significant heat loss to the atmosphere (~120 W/m2). Further analysis using horizontal dispersion coefficients revealed surface water convergence and downwelling in areas like MD′s western side and HG region, primarily dominated by anticyclonic eddies (94.44%). This influence on local ocean vertical motion, with wind conditions being a key factor favoring anticyclonic eddy formation in the recirculation area, suggests a significant role of eddies in the oceanic processes of the Fram Strait′s recirculation zone. |
