Intraseasonal Variability of Full‐Depth Currents in the Philippine Sea

Abstract

AbstractIntraseasonal 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.