Semiannual Variability of Middepth Zonal Currents along 5 degrees N in the Eastern Indian Ocean: Characteristics and Causes
Semiannual Variability of Middepth Zonal Currents along 5 degrees N in the Eastern Indian Ocean: Characteristics and Causes
复制标题
东印度洋北纬5度中深纬向流半年变化特征及成因
DOI：
10.1175/jpo-d-19-0089.1
复制
发表时间：
2019
影响因子：
3.5
通讯作者：
Li Jian
中科院分区：
文献类型：
--
作者：
Huang Ke;Wang Dongxiao;Han Weiqing;Feng Ming;Chen Gengxin;Wang Weiqiang;Chen Ju;Li Jian
东印度洋（5°N, 90.5°E）系泊4年（2014-17年）纬向流观测数据显示，中深度（~1200 m）存在强烈的半年周期，垂直结构明显。然而，这种明显的中深度半年变率与局地风强迫不一致，局地风强迫显示出一个主要的年循环。通过添加再分析产品和连续分层线性海洋模型，阐明了这种沿5°N的独特中深度变化的根本原因。结果表明，观测到的5°N中深度纬向流的季节变化主要是由赤道附近半年风强迫的边界反射罗斯比波引起的。当地风力驱动的罗斯比波的贡献要小得多。理论上的Wentzel-Kramers-Brillouin射线路径进一步证实了东印度洋系泊区域中深信号的强烈半年变率在很大程度上是长罗斯比波在半年时间尺度上传播能量的陡峭角度的表现。由于罗斯比波的平滑轨迹受到当地年风的推动，年信号仅在上部和西段（75°-80°E）有意义。进一步分析表明，沿5°N方向的中深度纬向流与赤道对称罗斯比波每半年发生一次。因此，在5°S附近的中深度也应该存在类似的纬向流动。
Four-year (2014–17) zonal current data observed by a mooring at (5°N, 90.5°E) in the eastern Indian Ocean show a strong semiannual cycle in the middepth (~1200 m) with distinct vertical structure. This pronounced middepth semiannual variability, however, is inconsistent with the local wind forcing, which shows a predominant annual cycle. The underlying causes for this unique middepth variability along 5°N were elucidated with the addition of a reanalysis product and a continuously stratified linear ocean model. The results suggest that the observed seasonal variability in the middepth zonal flow at 5°N is primarily caused by boundary-reflected Rossby waves forced by the remote semiannual winds along the equator. Contribution from the locally wind-forced Rossby waves is much less. The theoretical Wentzel–Kramers–Brillouin ray paths further verify that the strong semiannual variability of the middepth signals over a moored region in the eastern Indian Ocean is largely a manifestation of the steep angles of propagating energy of the long Rossby waves at semiannual time scale. The annual signals are only significant in the upper and western sections (75°–80°E) as a result of the smooth trajectories of Rossby waves forced by local annual winds. Further analysis reveals that the middepth zonal currents along 5°N are expected to be associated with equatorial symmetric Rossby waves at semiannual period. Consequently, similar zonal flows should also exist in the middepth near 5°S.