Title: Temporal variations in internal tide multimodal structure on the continental shelf, South China Sea

Journal: Chinese Journal of Oceanology and Limnology, 35(1): 70–78

Authors: GAO D. -L., G. -Z. JIN*, and X. -Q. Lv

Abstract:Temporal variations in multimodal structures of diurnal (D1) and semidiurnal (D2) internal tides were investigated on the continental slope of the Dongsha Plateau, based on 2-month moored acoustic Doppler current profiler observations. Harmonic analysis indicated that the D1 components (K1 and O1) dominated the internal tide field. The vertical structure of the K1 constituent presented a first-mode structure while the M2 constituent seemed to exhibit a high-mode structure. Amplitude spectra analysis of the current data revealed differences in baroclinic current amplitudes between different water depths. Temporal variations in modal structures ware analyzed, based on the D1 and D2 baroclinic tides extracted from the baroclinic velocity field with band-pass filters. Analysis showed that the magnitude of the D1 internal tide current was much larger than the D2 current, and temporal variations in the modal structure of the D1 internal tide occurred on an approximately fortnightly cycle. The EOF analyses revealed temporal transformation of multimodal structures for D1 and D2 internal tides. The enhancement of the D1 internal tide was mainly due to the superposition of K1 and O1, according to the temporal variation of coherent kinetic energy.