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

以往的观测表明，东海大陆坡黑潮下存在着深逆流。但其在大陆坡上的持续性和沿着的空间范围尚未明确。2004年11月至2006年11月，我们在27-29° N斜坡区的4个位置进行了为期2年的锚定海流计测量，并观测了10幅包含深层逆流的流速剖面和水文剖面快照。在除去黑潮锋面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层逆流。中、北方陆坡区的深逆流结构存在差异，其边界对应于黑潮与大陆坡分离的气候平均位置。深逆流的位置在中部斜坡区比北方斜坡区深。深层逆流具有明显的季节性，尤其是在中央斜坡区，即，在冬春季节，周期为1-2个月的周期性逆流被组织成一个持续的逆流，此时黑潮锋弯曲的周期小于20天的趋势趋于减弱。从能量逆级联和黑潮分离两个方面讨论了中陆坡区和北方陆坡区持续性深层逆流的形成机制。

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.