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- Title
Intraseasonal Variability of Full‐Depth Currents in the Philippine Sea.
- Authors
Yuan, Xin; Wang, Qingye; Hu, Dunxin; Feng, Junqiao; Wang, Fujun; Tian, Zhizhao
- Abstract
Intraseasonal variability (ISV) in the meridional velocity of multi‐layer currents in the Philippines Sea was investigated using near full‐depth mooring observations deployed at 130°E, 11°N from September 2015 to October 2019 and the reanalysis data from 2015 to 2019. Prominent bimodal ISVs structures were detected in the power spectra of the meridional velocities at 45‐ and 62‐days, occurring from the surface through to the bottom. Further analysis suggested that the identified ISV of 62‐days in the upper 1,500 m was controlled by large‐scale oceanic Rossby waves with a zonal wavelength of 687 km. The full‐depth 45‐days fluctuation is limited by the entire zonal width of the Philippines Basin, which is approximately 900 km. The 45‐days variability modulated by the barotropic Rossby normal mode triggered by resonant wind forcing in the key region of 126°–140°E and 5°–13°N. Whereas the deep‐layer 62‐days fluctuation is limited by the basin width near the bottom (5,700 m), which is approximately 640 km. In addition, two super‐intense ISV events occurred in the upper layers following the 2015/16 and 2018/19 El Niño events, which generally lagged the Niño 3.4 index by six/seven months. This study reveals the upper‐layer ocean ISVs response in the western Pacific following El Niño events and triggering of the deep‐layer ocean ISVs by the actual basin scale. Our findings provide a better understanding of the variations in full‐depth currents in the western Pacific Ocean. Plain Language Summary: Compared to the upper ocean variability, which is well‐known to oceanographers, the variability of the intermediate‐deep ocean is mysterious, because it is largely limited by the paucity of in situ observations in the deep ocean. The 4‐year continuous direct current measurements used in this study are invaluable for studying the intraseasonal variability (ISV) of meridional velocity in the Philippine Sea. Near full‐depth measurements revealed a bimodal ISV structure with 45‐, and 62‐days in the power spectrum of the meridional velocity. Further analysis demonstrated that the 62‐day ISV of the meridional velocity in the upper ocean was mainly controlled by the westward‐propagation first‐mode baroclinic Rossby wave, and deep‐layer ISVs of the meridional velocity were modulated by barotropic Rossby normal mode that depended on the actual Philippine basin scale. In addition, the two super‐intense ISV events observed in the upper‐layer ocean in the western Pacific were strongly associated with El Niño events. This study revealed a previously unclear variability in deep‐layer currents triggered by the actual basin scale, which greatly enriched our understanding of full‐depth circulation variation in the Philippine Sea. Key Points: Bimodal intraseasonal variability (ISV) in the full‐depth meridional velocity was observed in the Philippine SeaUpper‐layer 62 days ISV was controlled by the first‐mode baroclinic Rossby wave, and its intensity increased dramatically after El NiñoFull‐depth 45 days and deep‐layer 62 days ISVs were modulated by the barotropic Rossby normal mode and triggered by resonant wind forcing
- Subjects
EL Nino; PACIFIC Ocean currents; ROSSBY waves; WIND pressure; POWER spectra
- Publication
Journal of Geophysical Research. Oceans, 2024, Vol 129, Issue 5, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2023JC019827