A numerical study on the relationships of the variations of volume transport around the China seas

• Reproduction of the ocean circulation in the western North Pacific and around the China seas.
• Three kinds of time scale variations are found in the VT through 8 transects.
• Seasonal variation is the most prominent for transects around the China seas.
• Subseasonal variation is controlled by the reversal monsoon winds in the China seas.
• Intra-seasonal variation is associated with local small scale winds and mesoscale features.

Three dimensional oceanic circulations in the North Pacific Ocean are simulated using the Regional Ocean Model System (ROMS). The model very well reproduces the main oceanic circulation patterns and the hydrodynamic structures in the North Pacific Ocean, especially in the China seas. Eight transects around the China seas are selected to analyze volume transport and their relationships. The simulated mean volume transport and their standard deviations are in good agreement with previous studies and observations in the Taiwan Strait (TWS, 1.79 ± 0.96 Sv, 1 Sv ≡ 106 m3/s), East of Taiwan (PCM, 20.03 ± 5.19 Sv), Tokara Strait (TKS, 19.22 ± 3.22 Sv), Tsushima Strait (TUS, 2.14 ± 0.47 Sv), Luzon Strait (LUS, 4.57 ± 4.13 Sv), Karimata Strait (KMS, 1.28 ± 0.65 Sv), East of Luzon Island (ELI, 13.93 ± 5.31 Sv), and 137°E across the North Equatorial Current from 10°N to 20°N (137E, 44.0 ± 9.90 Sv). Three kinds of time scale variations (seasonal, sub-seasonal, intra-seasonal) were found in the volume transport through these transects with over the 95% significance level. The power spectrum density of the seasonal variation was almost one order of magnitude larger than the others for transects around the China seas. Coherency relationships among the volume transport through transects were analyzed. The results indicate that the seasonal time scale variations in volume transport around the China seas were dominated by the monsoon winds, but the Kuroshio along its pathway was relatively stable with small seasonal variation; the sub-seasonal time scale variations were associated with strong monsoon reversal winds; and the intra-seasonal variations were complex and weak, associating with local small scale winds and mesoscale eddy activities along the Kuroshio.