Cite this paper:
ZHAO Jun, LI Yuanlong, WANG Fan. Seasonal variation of the surface North Equatorial Countercurrent (NECC) in the western Pacific Ocean[J]. Journal of Oceanology and Limnology, 2016, 34(6): 1332-1346

Seasonal variation of the surface North Equatorial Countercurrent (NECC) in the western Pacific Ocean
ZHAO Jun1, LI Yuanlong1,2, WANG Fan1,3
1 Key Laboratory of Ocean Circulation and Waves, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China;
2 Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, Colorado, USA;
3 Function Laboratory for Ocean Dynamics and Climate, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266000, China
Abstract:
The North Equatorial Countercurrent (NECC) is an important zonal flow in the upper circulation of the tropical Pacific Ocean, which plays a vital role in the heat budget of the western Pacific warm pool. Using satellite-derived data of ocean surface currents and sea surface heights (SSHs) from 1992 to 2011, the seasonal variation of the surface NECC in the western tropical Pacific Ocean was investigated. It was found that the intensity (INT) and axis position (YCM) of the surface NECC exhibit strikingly different seasonal fluctuations in the upstream (128°-136°E) and downstream (145°-160°E) regions. Of the two regions, the seasonal cycle of the upstream NECC shows the greater interannual variability. Its INT and YCM are greatly influenced by variations of the Mindanao Eddy, Mindanao Dome (MD), and equatorial Rossby waves to its south. Both INT and YCM also show semiannual signals induced by the combined effects of equatorial Rossby waves from the Central Pacific and local wind forcing in the western Pacific Ocean. In the downstream region, the variability of the NECC is affected by SSH anomalies in the MD and the central equatorial Pacific Ocean. Those in the MD region are especially important in modulating the YCM of the downstream NECC. In addition to the SSH-related geostrophic flow, zonal Ekman flow driven by meridional wind stress also plays a role, having considerable impact on INT variability of the surface NECC. The contrasting features of the variability of the NECC in the upstream and downstream regions reflect the high complexity of regional ocean dynamics.
Key words:    North Equatorial Countercurrent (NECC)    seasonal variation    western Pacific Ocean    wind stress   
Received: 2015-04-12   Revised: 2015-06-24
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