Deep countercurrent beneath the Kuroshio on the continental slope in the East China Sea

以往的观测表明，东海陆坡黑潮下存在深层逆流。然而，其在大陆斜坡上的持续性和空间范围尚未明确。2004年11月至2006年11月，我们在靠近27-29°N的斜坡区进行了为期2年的系泊海流测量，并观测了10个包含深逆流的速度和水文剖面快照。在消除了黑潮前弯曲引起的高频波动（周期短于约20天）的速度记录中，可以清楚地识别出深逆流。深逆流构造在中部和北部斜坡区存在差异，其边界对应于黑潮与大陆斜坡分离的气候平均位置。深逆流的位置在中部斜坡区较北部斜坡区深。深逆流具有明显的季节固定特征，特别是在中部坡区，即1 ~ 2个月周期变化的周期性逆流在冬春季节被组织成持续的逆流，此时周期短于20天的黑潮锋曲流趋于减少。讨论了形成中部和北部斜坡区持续深层逆流的机制，并分别与逆能量级联和大陆斜坡黑潮分离有关。

Previous observations have indicated that the deep countercurrent is present beneath the Kuroshio on the continental slope in the East China Sea. However, its persistency and spatial extent along the continental slope have not been clarified as yet. We carried out 2-years moored current meter measurements at four locations in the slope area near 27-29° N, and observed ten snapshots of velocity and hydrographic sections containing the deep countercurrent for the period November 2004 and November 2006. The deep countercurrents were clearly identified to the velocity records in which high-frequency fluctuations (periods shorter than about 20 days) due to Kuroshio front meanders were removed. Structures of the deep countercurrent had differences between the central and northern slope areas, the boundary of which corresponded to the climatological mean position where the Kuroshio separates from the continental slope. The location of the deep countercurrent was deeper in the central slope area than in the northern one. The deep countercurrent had a clear season-fixed nature especially in the central slope area, i.e., periodic countercurrents that vary with periods of 1-2 months were organized into a persistent countercurrent in winter-spring seasons, and in this time the Kuroshio front meanders with periods shorter than 20 days tended to diminish. Mechanisms that form the persistent deep countercurrents in the central and northern slope areas are discussed in relation to the inverse energy cascade and the Kuroshio separation fro n the continental slope, respectively.