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Two Flavors of Intraseasonal Variability and Their Dynamics in the North Equatorial Current/Undercurrent Region
May 31,2022

Zhenxiao Wang, Linlin Zhang, Yuchao Hui, Fan Wang and Dunxin Hu

Published in Frontiers in Marine Science, March 2022

Significant surface-intensified and subsurface-intensified intraseasonal variability (ISV) of the North Equatorial Current/Undercurrent with different periods are detected to coexist with mooring ADCP measurements at 13°N, 130°E. The ISV of the currents in the upper 200 m has a relatively shorter period of 45 days, while the period of the subsurface-intensified ISV between 400 and 800 m is around 85 days. By combining with sea surface height measurements from satellite altimeters and outputs from an eddy-resolving ocean general circulation model, the origin and dynamic mechanism of the two flavors of ISV are investigated. Eddy trajectory tracking and energy analysis indicate that both the surface-intensified and subsurface-intensified ISV are related to locally generated meso-scale eddies near the mooring sites. Stability analysis suggests the surface-intensified ISV is related to the baroclinic instability induced by the vertical velocity shear of the North Equatorial Current. While the generation of the subsurface-intensified ISV is more complex and is partly related to the enhanced barotropic instability induced by the intensified horizontal shear of the subsurface zonal background flow.

Figure . (A) Trajectories (red curves) of all the surface eddies that can affect the currents at 13°N, 130°E during 2010–2016 derived from the AVISO data. (B) same as (A), but for subsurface eddies derived from OFES outputs in the same period. The green dots denote the origins of those eddies and the black dots denote their destinations. The yellow circle denotes the region centering at the mooring location with a radius of 150 km.

Wang, Z., Zhang, L., Hui, Y., Wang, F., and Hu, D. 2022. Two Flavors of Intraseasonal Variability and Their Dynamics in the North Equatorial Current/Undercurrent Region, Front. Mar. Sci., 9, https://doi.org/10.3389/fmars.2022.845575

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