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標題: | 全球暖化下黑潮的變化與未來推估 Future Projection and Variability of Kuroshio Under Global Warming |
作者: | 黃偌栩 Jo-Hsu Huang |
指導教授: | 曾于恒 Yu-Heng Tseng |
關鍵字: | 黑潮,CMIP6,動能,正壓流函數,副熱帶模態水,斜壓性變化, Kuroshio,CMIP6,Kinetic energy,Barotropic stream function,Subtropical mode water,Baroclinic Change, |
出版年 : | 2023 |
學位: | 碩士 |
摘要: | 黑潮為西北太平洋之西方邊界流,透過其顯著的熱量傳輸以及海氣交互作用,可以對海洋的生態、天氣甚至是氣候造成很大的影響。然而,過去對於其未來暖化情境下的變化,與其背後的主導機制,並沒有明確且一致的結論。有些研究認為,暖化下的聖嬰現象或極區震盪趨勢,可以增強中緯度的反氣旋式風場,使該處的黑潮迴流增強;有些研究則認為暖化的副熱帶模態水,經由大洋環流傳輸到黑潮的東側,使黑潮的斜壓性特徵增強、上層流速增加。
本研究使用28個CMIP6低解析度模式在SSP5-8.5未來暖化情境的模擬進行集合分析。結果顯示整體而言,日本沿岸黑潮的動能與流量皆有增強的趨勢,而東海黑潮則有減弱的現象。此外,東海黑潮的動能變化有上層300公尺增強,而下層減弱的斜壓性變化。然而,因為琉球島鏈周圍在上層300公尺有反氣旋式的環流變化,使得此處的淨流量並沒有明顯的變化。相較至下,5個高解析度模式集合顯示,日本沿岸黑潮及黑潮洄流的動能及流量皆有更顯著的增強趨勢,且黑潮延伸流域有往極區移動的情形。此外,東海黑潮在上層為減弱的趨勢,與下層變化相同,表示在高解析度模式中,東海黑潮並沒有顯著的斜壓性變化。本研究也發現不論何處的黑潮,不同模式中的經向傳輸變化與風應力旋度變化皆呈顯著的負相關,且日本沿岸黑潮變化對風應力旋度變化在高解析度模式中更加敏感。進一步的敏感度測試顯示,暖化後的海表溫度主導了北緯35度以南的黑潮在上層300公尺的變化,而風應力旋度則主導300公尺以下的變化。等密面上增暖的海水透過副熱帶模態水傳輸,使黑潮東側的海溫變得更暖,增強了跨黑潮的緯向密度梯度,因此向北的黑潮流速增加。 Kuroshio plays a critical role in the ocean ecosystem, weather, and even climate in the Western North Pacific through its significant heat transport and air-sea interaction. The future change and dominant mechanism behind it under global warming remain unclear. Some previous studies suggested a negative midlatitude wind stress curl tendency, potentially driven by El Niño or Arctic Oscillation, may accelerate the Kuroshio recirculation. The other studies found that the warmer subtropical mode water might be transported to the east of the Kuroshio along the isopycnals, enhancing the upper-layer velocity under a warmer climate. Our analysis of the ensemble of 28 CMIP6 low-resolution models in the SSP5-8.5 future scenario projection shows that the kinetic energy and transport tendency of the Kuroshio along Japanese coast (JP-Kuroshio) is positive while the ECS-Kuroshio is negative. Additionally, the kinetic energy of ECS-Kuroshio increases in the upper 300 m and decreases below 300 m (i.e., baroclinic change). However, the transport of it does not change significantly in the upper 300 m because of the anticyclonic circulation change surrounding the Ryukyu Island chain. Compared with the result above, the ensemble of 5 eddy-permitting models shows that the kinetic energy and transport of JP-Kuroshio, including the southern recirculation gyre, enhances more dramatically and the Kuroshio extension moves poleward, while the ECS-Kuroshio decreases in the whole water column. This suggests the consistent baroclinic increase in ECS is not evident in the eddy-permitting models. We also find that the meridional transport change negatively correlates well with the wind stress curl change across different models. Particularly, the meridional transport change of the JP-Kuroshio is more sensitive to the wind stress curl in eddy-permitting models. Further ocean model experiments suggest that warmer sea surface temperature dominates the Kuroshio change in the upper 300 m to the south of 35°N while the impact of wind stress curl determines the change below 300 m. Warmer isopycnal temperature transport through the subtropical mode water pathway increases the zonal gradient across the Kuroshio and intensify the meridional velocity. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/90102 |
DOI: | 10.6342/NTU202301059 |
全文授權: | 同意授權(全球公開) |
顯示於系所單位: | 海洋研究所 |
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