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- Title
Effect of the Intensified Sub‐Thermocline Eddy on Strengthening the Mindanao Undercurrent in 2019.
- Authors
Azminuddin, Fuad; Lee, Jae Hak; Jeon, Dongchull; Shin, Chang‐Woong; Villanoy, Cesar; Lee, Seok; Min, Hong Sik; Kim, Dong Guk
- Abstract
The northward‐flowing Mindanao Undercurrent (MUC) was directly measured by acoustic Doppler current profilers from a subsurface mooring at about 8°N, 127°E during 2 years (November 2017–December 2019). Its depth covers a range from 400 m to deeper than 1,000 m with its core appearing at around 900 m. The mean velocity of MUC's core was approximately 5.8 cm s−1 with a maximum speed of about 47.6 cm s−1. The MUC was observed as a quasi‐permanent current with strong intraseasonal variability (ISV) with a period of 70–80 days. Further analyses with an eddy‐resolving circulation model output suggest that the ISV is closely related to sub‐thermocline eddies (SEs). In this study, two types of SEs near the Philippine coast are disclosed: the westward propagating SE (SE‐1) and the quasi‐stational SE southeast of Mindanao Island (SE‐2). The SE‐1 has both cyclonic and anticyclonic polarities with the propagation speed of 7–8 cm s−1, while the SE‐2 is an anticyclonic eddy that moves erratically within 4–8°N, 127–130°E with the mean translation speed of about 11 cm s−1. Even though the SE‐1 plays an important role in modulating the MUC, our results show that the observed strong MUC event (May–July 2019) is evidently induced by the intensified SE‐2 that moves northwestward. This study emphasizes that the SE‐2 when intensified, receives more energy from the strengthened New Guinea Coastal Undercurrent and loses the energy northward along the Philippine coast by intensifying the MUC. Plain Language Summary: The northward subsurface current east of the Philippine coast, called the Mindanao Undercurrent (MUC), plays an important role in water mass exchange between the hemispheres by transporting intermediate water originating in the South Pacific to the north. To better understand the MUC, a subsurface current meter mooring was deployed at about 8°N, 127°E for 2 years (November 2017–December 2019). The obtained data reveal that the MUC is a quasi‐permanent current with strong intraseasonal variability (ISV) with a period of 70–80 days. Further analyses with an eddy‐resolving circulation model output suggest that the ISV is closely related to sub‐thermocline eddies (SEs). In this study, two types of SEs near the Philippine coast are disclosed: the westward propagating SE and the quasi‐stationary SE southeast of Mindanao Island (SE‐2). The MUC at the observation site was shown to strengthen in May–July 2019 and appears to be driven by the intensified SE‐2. We found that the SE‐2 is empowered by receiving energy from the enhanced New Guinea Coastal Undercurrent, which flows further northwest than the average state. During the intensification phase, the SE‐2 moves toward the east coast of Mindanao Island, affecting the MUC strengthening. Key Points: Data from moored current meters and model outputs show the enhanced Mindanao Undercurrent (MUC) in 2019The intensified sub‐thermocline eddy southeast of Mindanao Island is found to cause the observed strong MUC eventThe behavior of this eddy is related to changes in the strength of the New Guinea Coastal Undercurrent
- Subjects
THERMOCLINES (Oceanography); EDDIES; OCEAN currents; WATER masses; SHATSKY Rise
- Publication
Journal of Geophysical Research. Oceans, 2022, Vol 127, Issue 2, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2021JC017883