基于再分析产品的西边界流趋势分析及其与北极海冰的联系

Trend analysis of the western boundary currents based on reanalysis products and its connection to Arctic sea ice

中文关键词:  西边界流  黑潮  湾流  趋势分析  海洋再分析产品  北极海冰

英文关键词:western boundary currents  Kuroshio  Gulf Stream  trend analysis  ocean reanalysis products  Arctic sea ice

中文摘要:

      黑潮和湾流是北半球重要的西边界流，其趋势演变对海气相互作用有关键性影响。由于观测时空覆盖不足和数值模式精度有限，当前准确表征黑潮和湾流的趋势变化面临较大挑战。利用两套海洋再分析产品（CORAv2.0和GREP数据集），从路径和强度两方面进行了1993－2016年黑潮和湾流变化的趋势分析，并结合北极海冰观测数据及地球系统模式研究了北极海冰对黑潮和湾流趋势演变的影响。结果显示两套海洋再分析产品均反映出70°W以东区域湾流存在减弱趋势，且在56°W以东湾流路径随时间向赤道方向移动。CORAv2.0数据显示黑潮出现明显增强趋势；而GREP数据中黑潮强度只在日本以东区域增强，140°E以东黑潮路径向极地方向移动。两套海洋再分析产品中黑潮 （湾流） 流速与观测的秋季北极海冰面积存在显著负 （正） 相关关系。通过地球系统模式设计北极海冰扰动试验，发现北极海冰消融导致的黑潮增强模态与CORAv2.0数据显示 的黑潮速度趋势十分吻合，并且模拟得到的湾流响应也与两套海洋再分析产品的趋势分析相一致，即北极海冰消融使黑潮增强，湾流减弱，并且湾流的路径向赤道方向移动。研究结果为厘清西边界流长期变化趋势与作用机制提供参考依据，同时也反映出海洋再分析产品在西边界流趋势分析中较高的应用价值。

英文摘要:

      The Kuroshio and the Gulf Stream are important western boundary currents in the Northern Hemisphere. Their trend evolutions play key roles in air-sea interaction. Owing to insufficient temporal and spatial coverage of observations and limited accuracy of numerical models, it is a big challenge to characterize the trend changes of the Kuroshio and the Gulf Stream precisely. Using two ocean reanalysis products (CORAv2.0 and GREP), trend analyses of the Kuroshio and the Gulf Stream from 1993 to 2016 are carried out in terms of both paths and intensities. Further, the impact of Arctic sea ice on the trend evolutions of the Kuroshio and the Gulf Stream is investigated through sea ice observations and the Coupled Earth System Model. The two ocean reanalysis products both show that the Gulf Stream experienced a weakening trend east of 70°W, accompanied by an equatorward shift east of 56°W during the period. CORAv2.0 reveals an obvious intensification of the Kuroshio, while GREP shows the Kuroshio strengthening only east of Japan, associated with a poleward shift east of 140°E. There is a significant negative (positive) correlation between the Kuroshio (Gulf Stream) velocity and the observed Arctic sea ice area in autumn. Arctic sea ice perturbation experiments are designed by the Coupled Earth System Model. The results reveal that the simulated enhancing Kuroshio due to Arctic sea ice loss is consistent with the Kuroshio velocity trend shown in CORAv2.0. The Gulf Stream response also matches the trend analysis by the two ocean reanalysis products, confirming that Arctic sea ice loss intensifies the Kuroshio but weakens the Gulf Stream, with the path of the Gulf Stream moving equatorward. The research provides a reference for clarifying the long-term trend and mechanisms of the west boundary currents and also reflects the high application value of marine reanalysis products in the trend analysis of the west boundary currents.