Journal of Oceanography

, Volume 68, Issue 5, pp 687–701 | Cite as

Isolation of sea surface salinity maps on various timescales in the tropical Pacific Ocean

  • Jian Chen
  • Ren Zhang
  • Huizan Wang
  • Yuzhu An
  • Peng Peng
  • Weitao Zhang
Original Article

Abstract

To isolate sea surface salinity (SSS) maps on seasonal, ENSO, decadal, and long-term trend timescales in the tropical Pacific Ocean, the ensemble empirical mode decomposition (EEMD) is applied on an SSS data set covering 1950–2009, concerning three key regions including the western equatorial Pacific Warm Pool (WP), South Pacific Convergence Zone (SPCZ), and Inter Tropical Convergence Zone (ITCZ); then a self-organizing map is performed on the intrinsic mode function maps decomposed by the EEMD, concerning the whole basin. The ENSO and decadal signals concern mainly the western Pacific, in contrast to the seasonal signal mostly notable in the east. (1) The modulated annual cycle has smaller (larger) amplitudes during El Niño (La Niña) years and later appearance of minima during El Niño years; one unique annual cycle is observed at the northwestern edge of the ITCZ lagging the well-known ITCZ cycle by ~3 months. (2) The pronounced 1999–2001 SSS-related La Niña event in the SPCZ was reinforced twice by the decadal shift in the 1990s; the eastern Pacific and central Pacific ENSO-related SSS features are compared. (3) The contrasted anomalies between the western equatorial and non-equatorial regions were pronounced during 1977–1996, whereas they were less pronounced during 1971–1976, 2005–2008, and a roughly opposite pattern appeared with strong and abrupt decrease shift prevailing in large areas over the southwestern basin during 1997–2004. (4) The freshening at the western equator and the saltening located east of the SPCZ SSS front together amplify the geographical SSS contrasts exhibited by the WP and SPCZ SSS fronts.

Keywords

Sea surface salinity Tropical Pacific Ocean Modulated annual cycle ENSO Decadal variability Long-term trend Ensemble empirical mode decomposition Self-organizing map 

Abbreviations

CP

Central Pacific

ECT

Equatorial Cold Tongue

EEMD

Ensemble empirical mode decomposition

EMD

Mode decomposition

ENSO

El Niño Southern Oscillation

EP

Eastern Pacific

EPFP

Eastern Pacific Fresh Pool

IMF

Intrinsic mode function

ITCZ

Inter Tropical Convergence Zone

MAC

Modulated annual cycle

NECC

North Equatorial Countercurrent

PDO

Pacific Decadal Oscillation

SECC

South Equatorial Countercurrent

SOI

Southern Oscillation Index

SOM

Self-organizing map

SPCZ

South Pacific Convergence Zone

SSS

Sea surface salinity

SST

Sea surface temperature

WP

Warm Pool

Notes

Acknowledgments

We would like to thank the two anonymous reviewers for their useful feedback and suggestions which have greatly helped to improve the manuscript. This work was supported by the Chinese National Natural Science Fund of Jiangsu Province (BK2011123) and Chinese National Natural Science Fund for young scholars (41005025/D0505). We benefited from some observed data sets made freely available including the French Sea Surface Salinity Observation Service (http://www.legos.obs-mip.fr/en/observations/sss/), Southern Oscillation Index (http://www.cpc.ncep.noaa.gov/data/indices/soi), and Pacific Decadal Oscillation Index (http://www.jisao.washington.edu/pdo/).

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Copyright information

© The Oceanographic Society of Japan and Springer 2012

Authors and Affiliations

  • Jian Chen
    • 1
  • Ren Zhang
    • 1
  • Huizan Wang
    • 1
  • Yuzhu An
    • 1
  • Peng Peng
    • 1
  • Weitao Zhang
    • 1
  1. 1.PLA Key Laboratory of Marine Environment, Institute of MeteorologyPLA University of Science and TechnologyNanjingChina

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