Strong near-inertial oscillations in geostrophic shear in the northern South China Sea |
| |
| Authors: | Zhenyu Sun Jianyu Hu Quanan Zheng Chunyan Li |
| |
| Institution: | (1) State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, 361005, Fujian, China;(2) Department of Atmospheric and Oceanic Science, University of Maryland, College Park, MD 20742, USA;(3) Department of Oceanography and Coastal Science, Coastal Studies Institute, Louisiana State University, Baton Rouge, LA 70803, USA |
| |
| Abstract: | With observational data from three Acoustic Doppler Current Profiler (ADCP) moorings, we detected strong near-inertial oscillations
(NIO) in the continental shelf region of the northern South China Sea in July 2008. The amplitude of the near-inertial current
velocity is much greater than that of diurnal and semi-diurnal tides. The power of the NIOs is strongest in the intermediate
layer, relatively weak in the surface layer, and insignificant in the near-bottom layer. The spectral analysis indicates that
the NIOs have a peak frequency of 0.0307 cph, which is 2% lower than the local inertial frequency, i.e., a red-shift. The
near-inertial wave has an upward vertical phase velocity, which involves a downward group velocity and energy flux. The estimated
vertical phase velocity is about 43 m day−1, corresponding to a vertical wave length of about 58 m. The horizontal scale of the NIOs is at least hundreds of kilometers.
This NIO event lasted for about 15 days after a typhoon’s passage. Given the northeastward background flow with significant
horizontal shear, both Doppler shift and shear flow modulation mechanisms may be responsible for the red-shift of the observed
NIOs. For the shear flow mechanism, the observed negative background vorticity and the corresponding effective Coriolis frequency
reduce the lower limit of admissible frequency band for the NIOs, causing the red-shift. Meanwhile, the mooring area with
the broadened frequency band acts as a wave-guide. The trapping and amplification effects lead to the relatively long sustaining
period of the observed NIOs. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
