Observed near-inertial kinetic energy in the Philippine Sea

Using 32 months of observational data from two acoustic Doppler current profiler (ADCP) moorings deployed at 18 degrees N, 125 degrees E and 18 degrees N, 126 degrees E, this study investigated the statistical characteristics of the near-inertial kinetic energy (NIKE) in the Philippine Sea. During the whole observational period, the ratio of the typhoon-induced NIKE to the total NIKE was only approximately 1/3, while processes other than typhoons contributed approximately 2/3 of the total NIKE. The research depth was divided into four layers to explore the relative importance of NIKE, and NIKE was found to contribute the highest proportion of total kinetic energy in the 400 similar to 600 m layer, not the 50 similar to 200 m layer. Four typical strong NIKE cases were found in months without any typhoon records, and the time-averaged NIKE at the core depth of these cases was much higher than that of the non-typhoon period. The vertical group velocity (Cgz) and generation mechanism of these events were examined. The NIOs basically propagated in the layer where they were generated with small C-gz values (between 0 and 5 m . d(-1)) and dissipated rapidly (within 10 days). Correlation analysis suggested that low-frequency flow vertical shear transferred energy into the near-inertial frequency band, leading to the spontaneous formation of NIKE. The ratio of NIKE generated by low-frequency flow vertical shear to the total NIKE in the nontyphoon period is 14.1%. In the presence of an anticyclonic eddy, wind-generated NIOs were captured at the edge and accumulated at the bottom of the eddy. The highest NIKE among these cases was caused by both low-frequency vertical shear and the eddy. (c) 2022 Published by Elsevier B.V.