Stronger Intraseasonal Variability Observed Below the Seasonal Thermocline in the Kuroshio East of Taiwan During 2014 and 2015

• Published in: Journal of geophysical research. Oceans 2021-07, Vol.126 (7), p.n/a
• Main Authors: Wang, Qingye, Yuan, Xin, Hu, Dunxin, Sasaki, Hideharu
• Format: Article
• Language: English
• Subjects: Altimetry; Coastal upwelling; Coastal waters; Coasts; Cold water; Deep layer; Depth; Eddies; Evolution; Geophysics; Meandering; Metalimnion; Mooring; Mooring systems; Ocean circulation; Ocean models; Oceanic eddies; Oceans; Seasonal thermocline; Seasonal variability; Seasonal variations; Thermocline; Upwelling; Variability; Variation; Velocity; Vortices; Water depth; Water temperature
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2021JC017194

Intraseasonal variability in the Kuroshio east of Taiwan was studied using moored observations at 23°N, 122°E from November 17, 2014 to September 5, 2015, high‐resolution ocean model data, and altimetry data. It is found for the first time that the observed meridional velocity has a peak signal at 50–60 days with a significant maximum variation at 200–600 m depth. Model outputs show that the 50–60‐day variability at the mooring station is related to meandering of the Kuroshio at 23°N. Both surface eddies, which can extend downward to ∼1,000 m depth, and coastal cold water upwelling associated with cyclonic eddies from deep layers can greatly change the isopycnal slope below ∼200 m depth at 23°N, 122°E, and their joint effect results in the maximum variation at 200–600 m depth. Ocean eddies southeast of Taiwan propagate northward along the current axis of the Kuroshio and have a large impact on intraseasonal variability. Case analysis indicates that the formation of ocean eddies or upwelling near the coast may be related to the Lüdao and Lanyu islands southeast of Taiwan or Kuroshio transport along the southern tip of Taiwan. In addition, the evolution of subsurface meridional velocity from mooring observations is inconsistent with that of the surface but is closely related to the evolution of local temperature below the seasonal thermocline. The maximum intraseasonal variability below the seasonal thermocline highlights the complex dynamics in the Kuroshio east of Taiwan. Plain Language Summary It is generally thought that the Kuroshio east of Taiwan is dominated by intraseasonal variability, especially on the ∼100‐day band observed along the PCM‐1 section and on the 70–200‐day band observed along the KTV1 section. However, in this study, we are the first to report that the Kuroshio east of Taiwan from a mooring at 23°N, 122°E in 2014–2015 has a 50–60‐day variability with a significant maximum variation at 200–600 m depth. The observed 50–60‐day variability is related to meandering of the Kuroshio at 23°N, and the maximum variation below the seasonal thermocline is because of the joint effect between surface eddies and upwelling near the coast. In addition to surface eddies from the ocean interior found in previous studies, this study highlights the important role of coastal upwelling from the deep layer in modulating the intraseasonal variability of the Kuroshio east of Taiwan. Key Points The meridional velocity at 23°N, 122°E has a 50–60‐day variability