Spatial distribution of the seasonal variability of the North Equatorial Current

The seasonal variability of the North Equatorial Current (NEC) is investigated with four moorings at 10.5°N, 13°N, 15.5°N, and 18°N along 130°E from September 2014 to September 2015 and five moorings at 8.5°N, 11°N, 12.5°N, 15°N and 17.5°N along 130°E collected during 2016 and 2017 cruises. Generally, the mooring data shows that the NEC is strongest during boreal spring and summer and weakest in autumn for the stations located at 8.5°N, 10.5°N, 11°N, 12.5°N, 13°N, 17.5°N and 18°N, but the seasonal phase is almost reversed at 15°N and 15.5°N. In the area east of 140°E and north of 10°N, as the seasonal cycle of the wind stress curl anomaly is almost identical at different latitudes, the Rossby waves play a dominant role in the spatial distribution of the seasonal NEC. As the latitude increases, the rate of decrease in the propagation speed of Rossby waves becomes slower, resulting that the delay of the seasonal sea surface height anomaly (SSHa) tends to be smaller. In the area east of 140°E and between 5°N and 10°N, the seasonal phase of SSHa is delayed more rapidly than that in the south of 5°N, which is the result of local wind and Rossby waves. In the area west of 140°E and from 7°N to 15°N, the seasonal phase of the wind stress curl anomaly advances sharply with increasing latitude, corresponding well to the meridional phase advance of the seasonal SSHa and surface NEC, suggesting that the local wind plays a dominant role.