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Interannual and interdecadal variability of the N orth E quatorial C ountercurrent in the W estern P acific
Author(s) -
Chen Xiao,
Qiu Bo,
Du Yan,
Chen Shuiming,
Qi Yiquan
Publication year - 2016
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2016jc012190
Subject(s) - climatology , empirical orthogonal functions , hindcast , pacific decadal oscillation , forcing (mathematics) , oceanography , hydrography , boundary current , geology , ocean current , pacific ocean , environmental science , sea surface temperature
Interannual and longer timescale variations of the North Equatorial Countercurrent (NECC) in the western Pacific are investigated using the multidecade (1960–2014) hindcast by the Ocean general circulation model for the Earth Simulator (OFES). The OFES‐simulated sea level and upper ocean circulation changes show favorable comparisons with available tide gauge data and repeat hydrographic surveys along the 137°E meridian. An empirical orthogonal function (EOF) analysis reveals that the low‐frequency NECC variability is dominated by two distinct modes. The first mode fluctuates interannually and shows strengthening and southward migration of the NECC concurrent with the development of El Niño events. Unlike the extratropical western Pacific Ocean circulation variability controlled by wind forcing west of the dateline, the interannual NECC variations are forced by equatorial wind forcing cumulative across the entire Pacific basin. The second mode of the NECC variability has an interdecadal timescale and is characterized by NECC's progressive weakening in strength, migrating poleward, and broadening in width over the past 50 years. These long‐term changes in NECC are caused by the corresponding changes in the trade wind system that weakened and expanded poleward in the past half a century across the Pacific basin.