A train of subsurface mesoscale eddies (SMEs) consisting of two cyclones and two anticyclones was observed in the northeastern South China Sea (NESCS) in 2015 by a mooring array. In contrast to the widely reported surface-intensified eddies, the SMEs had weak surface signals but showed maximum velocity at ～370 m with a magnitude of 17.2 cm s?1. The SMEs generally propagated westward with a speed of ～4.3 cm s?1, which resulted in a distinct ～120-day-period oscillations in the moored time series. Based on the concurrent velocity, temperature, and salinity from the mooring array, three-dimensional structures of the SMEs were constructed, which were then used to quantify water mass transports induced by them. The results revealed that all these SMEs were vertically tilted with an influence depth exceeding 1000 m. Water mass analysis suggested that the cyclonic and anticyclonic SMEs trapped the northwest Pacific water and the NESCS local water, respectively. The cyclones transported 1.00 ± 0.25 Sv (1 Sv ≡ 106 m3 s?1) North Pacific Intermediate Water westward into the NESCS during the 2-yr observation period, accounting for 61.7% of the observed volume transport through the Luzon Strait between 25.8 and 27.4σ0. Furthermore, it also showed that both the trapping and stirring effects of the SMEs induced an eastward heat transport across the Luzon Strait, but the role of the former was much more important than the latter. The present results suggested that the SMEs near the Luzon Strait may provide a novel route for the intermediate-layer water exchange between the NESCS and Pacific.
南海东北部观测到的次表层中尺度涡：动力学特征和水体质量输运
中文摘要：2015 年，锚定观测阵列在南海东北部 (NESCS) 观测到由两个气旋和两个反气旋组成的一列次表层中尺度涡 (SME)。与广泛被研究的表面强化涡旋相反，SME 具有微弱的表面信号，但在 ~370 m 处显示出17.2 cm s-1的最大速度。 SMEs 通常以约 4.3 cm s-1 的速度向西传播，这导致锚定观测数据时间序列中出现了显著的约 120 天周期的振荡信号。