Seasonal Variability Of The North Equatorial Current Transport In The Western Pacific Ocean

The seasonal variability of the North Equatorial Current (NEC) transport in theWestern Pacific Ocean is investigated using ECMWF Ocean Analysis/ReanalysisSystem3(ORA-S3). The result shows that the NEC transport (NT) across differentlongitudes west of the dateline all has a similar double-peak structure with twomaxima in summer and winter, and two minima in spring and autumn, respectively.This kind of structure can also be found in the NEC geostrophic transport (NGT) butstill with different magnitude and phase. These differences are mainly caused by theEkman transport induced by the local meridional wind and the transport caused by thenonzero velocity at the reference level, which is assumed to be zero in the NGTcalculation.In the present paper, the linear vorticity equation governing a1.5layer reducedgravity model is adopted to examine what role the wind plays in determing theseasonal variation of NGT. It is found that the annual cycle of NGT across thelongitudes west of the dateline is mainly controlled by the Ekman pumping inducedby the local wind, and the westward propagating Rossby waves induced by the remotewind. Further research demonstrates that the maximum in winter and minimum inspring of NGT in the study area are mostly attributed to the wind east of the dateline,whilst the maximum in summer and minimum in autumn are mostly attributed to thatwest of the dateline.