Extraction of Internal Tidal Currents and Reconstruction of Full-Depth Tidal Currents from Mooring Observations

Abstract

To obtain internal tidal currents and full-depth tidal currents from limited mooring observations, a method is put forward combining harmonic analysis and modal decomposition. Harmonic analysis is used to separate tidal currents of different constituents, and modal decomposition is used to calculate full-depth tidal currents of each mode. By adding the barotropic tidal currents to all the baroclinic ones, the full-depth tidal currents of each constituent are reconstructed. The feasibility and accuracy of the proposed method is tested by twin experiments. Then, the method is used to extract tidal currents of each mode and to reconstruct full-depth tidal currents for M 2 and K 1 from a 3-month-long time series of acoustic Doppler current data observed at a station in the northern South China Sea. Results indicate that the total kinetic energy (KE) of M 2 is 25% larger than that of K 1 . For M 2 , the first baroclinic mode is the dominant one, followed by the barotropic one, and the sum of these modes accounts for more than 90% of the total M 2 KE. Tidal constituent K 1 is dominated by the barotropic mode, which accounts for more than 90% of the total K 1 KE.

Reflection of K1 Internal Tides at the Continental Slope in the Northern South China Sea

“…Namely, time‐varying magnitudes of modes u n ( t ) and p n ( t ) retain their standard dimensions. They can be determined by least squares fitting (Cao et al., 2015; Nash et al., 2005; Zhao et al., 2010). With u n ( t ) and p n ( t ) obtained, depth‐integrated energy flux for each mode are calculated.…”

FES2014 global ocean tide atlas: design and performance

“…When extracting a comprehensive tidal spectrum from a sealevel time series, the question of frequency separation must be examined carefully (Cherniawsky et al, 2001). Not only can the contamination by non-tidal signals at the aliased frequency be comparable to a given constituent amplitude (especially the minor constituents), but also the minimum observation duration for a proper separation is greatly increased in the aliased frequency space.…”

A Strong Internal Solitary Wave with Extreme Velocity Captured Northeast of Dong-Sha Atoll in the Northern South China Sea

“…According to [25], full-depth barotropic currents and baroclinic currents from limited mooring observations can be obtained by combining harmonic analysis and modal decomposition. Harmonic analysis is used to calculate harmonic constants of the major constituents and predict the time series of each major tidal constituent.…”

“…Modal decomposition is carried out to obtain full-depth tidal currents of each mode by using the least-squares method [26]. It was found that when more than three vertical modes were considered in the calculation, the prescribed tidal currents could be reconstructed accurately [25].…”