Using high-resolution satellite-derived sea surface temperature (SST) data from September 1981 to December 2015, the present study develops a new index to detect the long-term variation in mesoscale eddy activity over the Kuroshio Extension (KE) region. This eddy activity index (EAI) highlights the strength of eddy-induced poleward heat transport and has obvious advantages over the other existing KE indices in depicting the low-frequency changes in KE eddy activity. An analysis of the EAI shows that over the long term, the KE eddy activity variability presents a significant spectral peak of about 8 years and is not directly modulated by wind-driven oceanic Rossby waves generated in the central North Pacific. When the EAI is positive, the strengthened KE eddy activity significantly enhances the heat release from ocean to atmosphere over the Kuroshio–Oyashio confluence region (KOCR). This induces an anomalous dipole pattern of near-surface baroclinicity over this region that can persist for up to 6 months, favoring a weakened and northward-moving East Asian jet, and vice versa. It is believed that the new EAI will facilitate future studies focusing on the climatic effects of the KE eddy activity variation.

中文翻译：

---

描述黑潮延伸区中尺度涡旋活动长期变化的指数

本研究使用1981年9月至2015年12月的高分辨率卫星海面温度（SST）数据，开发了一种新的指数来检测黑潮扩展（KE）区域中尺度涡旋活动的长期变化。该涡流活动指数（EAI）强调了涡流诱导的极向热传递的强度，并且在描述KE涡流活动的低频变化方面，与其他现有的KE指数相比，具有明显的优势。对EAI的分析表明，从长远来看，KE涡流活动的变化呈现出约8年的显着光谱峰值，并且不受北太平洋中部产生的风驱动海洋Rossby波的直接调制。当EAI为正时，增强的KE涡流活动显着增强了黑潮-矢潮汇合区（KOCR）从海洋到大气的热量释放。这导致该区域近地表斜压异常偶极子模式，这种异常偶极子模式可以持续长达6个月，这有利于东亚急流减弱并向北移动，反之亦然。可以相信，新的EAI将促进未来的研究，重点放在KE涡流活动变化的气候影响上。