Tidal and residual currents across the northern Ryukyu Island chain observed by ferryboat ADCP

Abstract

Ferryboat Acoustic Doppler Current Profiler (ADCP) data from 2003 to 2012 are used to estimate the tidal and residual currents across the northern Ryukyu Island chain (RIC) between the islands of Okinawa and Amamioshima. In this region, the M2 tide current is the strongest tidal component, and the K1 tide current is the strongest diurnal tidal component. The corresponding maximum amplitudes are 40 and 34 cm s−1, respectively. After removal of the tidal currents, the mean volume transport, 1.5 ± 2.7 Sv, flows into the East China Sea (ECS) from the western North Pacific through four channels in this area. In an empirical orthogonal function (EOF) analysis performed to clarify the temporal and spatial variability of currents through the four channels, the first two EOF modes account for 71% and 18% of the total variance, respectively. The EOF1 mode shows a clear bottom‐intensified mode through the deep channel, which is likely to be formed by the propagation of bottom‐trapped long topographic Rossby wave caused by the impingement of westward‐propagating mesoscale eddies upon the eastern slope of the northern RIC. The EOF2 mode has significant seasonal variability and may be driven by the wind stress prevailing over the Kuroshio flow region around the northern RIC in October–November. This study provides observational evidence of the water exchanges across the northern RIC, which is essential for constructing a circulation scheme in the North Pacific subtropical western boundary region.

Comprehensive Observational Features for the Kuroshio Transport Decreasing Trend During a Recent Global Warming Hiatus

“…A total of 1,234 velocity data tracks were available, of which 364 tracks had issues with missing data. Details of the ADCP data processing methodology have been reported in previous studies (Liu et al., 2017; Zhu et al., 2017). Using this data set, absolute Kuroshio transport through the Tokara Strait was obtained more accurately compared to previous estimates.…”

Tempo‐Spatial Variations of the Kuroshio Current in the Tokara Strait Based on Long‐Term Ferryboat ADCP Data

“…From January 2003 to March 2012, Kagoshima University conducted full‐depth acoustic Doppler current profiler (ADCP) measurements across the Tokara Strait, using the round‐trip ferryboat Naminoue between Kagoshima and Okinawa (Liu et al, ; Zhu et al, ). The repeated full‐depth ferryboat ADCP surveys provide unprecedented temporal and spatial resolution to resolve the variation in the Kuroshio across the Tokara Strait.…”

ENSO‐Related Interannual Variability of the Kuroshio in the East China Sea Since the Mid‐2000s

“…(2014) and Z. Liu et al. (2017), in which the sea water was exchanged between the ECS and the western North Pacific across the Ryukyu Islands chain through the mesoscale eddies, affecting the volume transport of the ECS‐Kuroshio.…”