Seasonal variations of the equatorial undercurrent (EUC) termination in the Eastern Pacific, and their mechanism were examined using the Estimating the Circulation and Climate of the Ocean, Phase Ⅱ(ECCO2). The ECCO2 reproduced a weak and shallow eastward EUC east of the Galapagos Islands, with annual mean transport of half of EUC to the west of the Islands. The diagnosis of zonal momentum equation suggests that the zonal advection (nonlinear terms) drives the EUC beyond the Islands rather than the pressure gradient force. The EUC in the Far Eastern Pacific has the largest core velocity in boreal spring and the smallest one in boreal summer, and its volume transport exhibits two maxima in boreal spring and autumn. The seasonal variability of the EUC in the Eastern Pacific is dominated by the Kelvin and Rossby waves excited by the zonal winds anomalies in the central and Eastern Pacific that are associated with the seasonal relaxation or intensification of the trade wind. In the Far Eastern Pacific to the east of 120°W, the eastward propagation Kelvin waves play a dominate role in the seasonal cycle of the EUC, results in a semiannual fluctuation with double peaks in boreal spring and autumn. A construction of water mass budget suggests that approximately 24.1％ of the EUC water east of 100°W has upwelled to the mixed layer by 0.35 m/d. The estimated upwelling is strongest during boreal autumn and weakest during boreal winter. It is also found that approximately 42.6％ of the EUC turns westward to feed the south equatorial current (SEC), 13.2％ flows north of the equator, and 20.1％ flows south of the equator, mainly contributing to Peru-Chile undercurrent.

Jie WANG;Xuezhi BAI;Hengling LENG

College of Oceanography,Hohai University,Nanjing 210098,China;Key Laboratory of Marine Hazards Forecasting,Ministry of Natural Resources,Hohai University,Nanjing 210098,China

海洋湖沼学报（英文版）

[1]Jie WANG;Xuezhi BAI;Hengling LENG-.Examination of seasonal variation of the equatorial undercurrent termination in the Eastern Pacific diagnosed by ECCO2)[J].海洋湖沼学报（英文版）,2022(03):870-890

undercurrent,semiannual,upwelled

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