Frequency Shift of Near Inertial Waves in the South China Sea

Arnaud Le Boyer1, Matthew H Alford2,3, Robert Pinkel4, Tyler Hennon2, Yiing Jang Yang5, Dong S Ko6 and Jonathan D Nash7, (1)Scripps Institution of Oceanography, MPL, San Diego, CA, United States, (2)Scripps Institution of Oceanography, La Jolla, CA, United States, (3)University of California San Diego, Scripps Institution of Oceanography, La Jolla, CA, United States, (4)Univ California San Diego, La Jolla, CA, United States, (5)National Taiwan University, Taipei, Taiwan, (6)Naval Research Lab., Oceanography, Stennis Space Center, MS, United States, (7)Oregon State University, Corvallis, OR, United States
Despite sufficient wind forcing, internal waves in the South China Sea do not exhibit the strong near-inertial wave (NIW) peak that is typical in most of the world oceans. Using data from 10 contemporaneous moorings deployed in summer 2011, we show that the Kuroshio and its mesoscale activity together with strong isopycnal vertical tidal displacements are likely candidates for the redistribution of the NIW signature over a wide vertical wavenumber-frequency range. This redistribution obscures the NIWs signature in an Eulerian frequency spectrum. NIWs are still present, but their observation requires the use of time-dependent vertical wavenumber-frequency spectra computed in an isopycnal-following reference frame.