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


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.


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



Central Pacific


Equatorial Cold Tongue


Ensemble empirical mode decomposition


Mode decomposition


El Niño Southern Oscillation


Eastern Pacific


Eastern Pacific Fresh Pool


Intrinsic mode function


Inter Tropical Convergence Zone


Modulated annual cycle


North Equatorial Countercurrent


Pacific Decadal Oscillation


South Equatorial Countercurrent


Southern Oscillation Index


Self-organizing map


South Pacific Convergence Zone


Sea surface salinity


Sea surface temperature


Warm Pool



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 (, Southern Oscillation Index (, and Pacific Decadal Oscillation Index (


  1. Alory G, Maes C, Delcroix T, Reul N, Illig S (2012) Seasonal dynamics of sea surface salinity off Panama: the Far Eastern Pacific Fresh Pool. J Geophys Res 117:C04028. doi:10.1029/2011JC007802 CrossRefGoogle Scholar
  2. Barbosa SM, Andersen OB (2009) Trend patterns in global sea surface temperature. Int J Climatol 29:2049–2055. doi:10.1002/joc.1855 CrossRefGoogle Scholar
  3. Bendat JS, Piersol AG (1986) Random data: analysis and measurement procedures, 2nd edn. Wiley, New YorkGoogle Scholar
  4. Boyer TP, Levitus S (2002) Harmonic analysis of climatological sea surface salinity, J Geophys Res 107(C12):8006. doi:10.1029/2001JC000829 Google Scholar
  5. Boyer TP, Levitus S, Antonov JI, Locarnini RA, Garcia HE (2005) Linear trends in salinity for the World Ocean, 1955–1998. Geophys Res Lett 32:L01604. doi:10.1029/2004GL021791 CrossRefGoogle Scholar
  6. Cabanes C, Cazenave A, Provost CL (2001) Sea level rise during past 40 years determined from satellite and in situ observations. Science 294:840–842CrossRefGoogle Scholar
  7. Cane M, Clement A, Kaplan A, Kushnir Y, Pozdnyakov D, Seager R, Zebiak SE, Murtugudde R (1997) Twentieth-century sea surface temperature trends. Science 275:957–960CrossRefGoogle Scholar
  8. Compo GP, Sardeshmukh PD (2010) Removing ENSO-related variations from the climate record. J Clim 23(8):1957–1978. doi:10.1175/2009JCLI2735.1 CrossRefGoogle Scholar
  9. Cravatte S, Delcroix T, Zhang D, McPhaden M, Leloup J (2009) Observed freshening and warming of the western Pacific Warm Pool. Clim Dyn 33(4):565–589. doi:10.1007/s00382-009-0526-7 CrossRefGoogle Scholar
  10. Cronin M, McPhaden M (1998) Upper ocean salinity balance in the western equatorial Pacific. J Geophys Res 103:27567–27587CrossRefGoogle Scholar
  11. Delcroix T (1998) Observed surface oceanic and atmospheric variability in the tropical Pacific at seasonal and ENSO timescales: a tentative overview. J Geophys Res 103(C9):18611–18633. doi:10.1029/98JC00814 Google Scholar
  12. Delcroix T, Hénin C (1991) Seasonal and interannual variations of sea surface salinity in the tropical Pacific Ocean. J Geophys Res 96(C12):22135–22150. doi:10.1029/91JC02124 Google Scholar
  13. Delcroix T, McPhaden M (2002) Interannual sea surface salinity and temperature changes in the western Pacific warm pool during 1992–2000. J Geophys Res 107(C12):8002. doi:10.1029/2001JC000862 Google Scholar
  14. Delcroix T, Picaut J (1998) Zonal displacement of the western equatorial Pacific “fresh pool”. J Geophys Res 103(C1):1087–1098. doi:10.1029/97JC01912 Google Scholar
  15. Delcroix T, Hénin C, Porte V, Arkin P (1996) Precipitation and sea-surface salinity in the tropical Pacific. Deep Sea Res Part I 43:1123–1141CrossRefGoogle Scholar
  16. Delcroix T, Cravatte S, McPhaden MJ (2007) Decadal variations and trends in tropical Pacific sea surface salinity since 1970. J Geophys Res 112:C03012. doi:10.1029/2006JC003801 CrossRefGoogle Scholar
  17. Delcroix T, Alory G, Cravatte S, Corrège T, McPhaden M (2011) A gridded sea surface salinity data set for the tropical Pacific with sample applications (1950–2008). Deep Sea Res Part I 58(1):38–48. doi:10.1016/j.dsr.2010.11.002 CrossRefGoogle Scholar
  18. Deser C, Phillips A, Alexander M (2010) Twentieth century tropical sea surface temperature trends revisited. Geophys Res Lett 37:L10701. doi:10.1029/2010GL043321 CrossRefGoogle Scholar
  19. Durack PJ, Wijffels SE (2010) Fifty-year trends in global ocean salinities and their relationship to broad-scale warming. J Clim 23(16):4342–4362. doi:10.1175/2010JCLI3377.1 CrossRefGoogle Scholar
  20. Fedorov A, Philander G (2000) Is El Niño changing? Science 288:1997–2002CrossRefGoogle Scholar
  21. Giese BS, James AC (1999) Interannual and decadal variability in the tropical and midlatitude Pacific Ocean. J Clim 12:3402–3418CrossRefGoogle Scholar
  22. Gouriou Y, Delcroix T (2002) Seasonal and ENSO variations of sea surface salinity and temperature in the South Pacific Convergence Zone during 1976–2000. J Geophys Res 107(C12):8011. doi:10.1029/2001JC000830 Google Scholar
  23. Gu D, Philander SGH (1995) Secular change of annual and interannual variability in the tropics during the past century. J Clim 8:864–876CrossRefGoogle Scholar
  24. Hare S (1996) Low frequency climate variability and salmon production. Ph.D. dissertation, University of Washington, WashingtonGoogle Scholar
  25. Huang NE, Shen Z, Long SR, Wu MC, Shih EH, Zheng Q, Tung CC, Liu HH (1998) The empirical mode decomposition and the Hilbert spectrum for nonlinear and nonstationary time series analysis. Proc R Soc Lond 454A:903–995Google Scholar
  26. Kohonen T (1982) Self-organized formation of topologically correct features maps. Biol Cybern 43:59–69CrossRefGoogle Scholar
  27. Kohonen T (2001) Self-organizing maps, 3rd ed. In: Springer Ser Inf Sci, 30. Springer, New York, p 501Google Scholar
  28. Latif M, Kleeman R, Eckert C (1997) Greenhouse warming, decadal variability, or El Niño? An attempt to understand the anomalous 1990s. J Clim 10:2221–2239CrossRefGoogle Scholar
  29. Lau KM, Weng H (1999) Interannual, decadal–interdecadal, and global warming signals in sea surface temperature during 1955–97. J Clim 12(5):1257–1267CrossRefGoogle Scholar
  30. Levitus S (1986) Annual cycle of salinity and salt storage in the world ocean. J Phys Oceanogr 16:322–343CrossRefGoogle Scholar
  31. Levitus S, Antonov J, Boyer T, Stephens C (2000) Warming of the world ocean. Science 287:2225–2229CrossRefGoogle Scholar
  32. Liu Y, Weisberg RH, Moors CNK (2006) Performance evaluation of the self-organizing map for feature extraction. J Geophys Res 111:C05018. doi:10.1029/2005JC003117 CrossRefGoogle Scholar
  33. Lukas R (2001) Freshening of the upper thermocline in the North Pacific subtropical gyre associated with decadal changes in rainfall. Geophys Res Lett 28:3485–3488CrossRefGoogle Scholar
  34. Maes C, Picaut J, Kuroda Y, Ando K (2004) Characteristics of the convergence zone at the eastern edge of the Pacific warm pool. Geophys Res Lett 31(11). doi:10.1029/2004GL019867
  35. Mantua N, Hare S (2002) The Pacific Decadal Oscillation. J Oceanogr 58:35–44CrossRefGoogle Scholar
  36. Mantua N, Hare S, Zhang Y, Wallace J, Francis R (1997) A Pacific interdecadal climate oscillation with impacts on salmon productions. Bull Am Meteorol Soc 78:1069–1079CrossRefGoogle Scholar
  37. Overland J, Salo I (1999) Salinity signature of the Pacific decadal oscillation. Geophys Res Lett 26:1337–1340CrossRefGoogle Scholar
  38. Philander SGH (1990) El Niño, La Niña and the Southern Oscillation. Elsevier, New York, p 289Google Scholar
  39. Picaut J, Ioualalen M, Menkes C, Delcroix T, McPhaden M (1996) Mechanism of the zonal displacements of the Pacific Warm Pool, implications for ENSO. Science 274:1486–1489CrossRefGoogle Scholar
  40. Picaut J, Ioualalen M, Delcroix T, Masia F, Murtugudde R, Vialard J (2001) The oceanic zone of convergence on the eastern edge of the Pacific Warm Pool: a synthesis of results and implications for ENSO and biogeochemical phenomena. J Geophys Res 106:2363–2386CrossRefGoogle Scholar
  41. Polo I, Ullmann A, Roucou P, Fontaine B (2011) Weather regimes in the Euro-Atlantic and Mediterranean Sector, and relationship with West African Rainfall over the 1989–2008 period from a self-organizing maps approach. J Clim 24:3423–3432. doi:10.1175/2011JCLI3622.1 CrossRefGoogle Scholar
  42. Qian C, Wu Z, Fu C, Zhou T (2010) On multi-timescale variability of temperature in China in modulated annual cycle reference frame. Adv Atmos Sci 27:1169–1182. doi:10.1007/s00376-009-9121-4 CrossRefGoogle Scholar
  43. Qian C, Wu Z, Fu C, Wang D (2011a) On changing El Niño: a view from time-varying annual cycle, interannual variability, and mean state. J Clim 24:6486–6499CrossRefGoogle Scholar
  44. Qian C, Wu Z, Yan Z (2011b) The role of changes in the annual cycle in earlier onset of climatic spring in northern China. Adv Atmos Sci 28:284–296. doi:10.1007/s00376-010-9221-1 CrossRefGoogle Scholar
  45. Rasmusson EM, Carpenter TH (1982) Variations in tropical sea surface temperature and surface wind fields associated with the Southern Oscillation/El Niño. Mon Weather Rev 110:354–384CrossRefGoogle Scholar
  46. Reverdin G, Frankignoul C, Kestenare E, McPhaden M (1994) Seasonal variability in the surface currents of the equatorial Pacific. J Geophys Res 99:20323–20344CrossRefGoogle Scholar
  47. Rodgers K, Friedrichs P, Latif M (2004) Tropical Pacific decadal variability and its relation to decadal modulations of ENSO. J Clim 17:3761–3774CrossRefGoogle Scholar
  48. Singh A, Delcroix T (2011) Estimating the effects of ENSO upon the observed freshening trends of the western tropical Pacific Ocean. Geophys Res Lett 38:L21607. doi:10.1029/2011GL049636 CrossRefGoogle Scholar
  49. Singh A, Delcroix T, Cravatte S (2011) Contrasting the flavors of El Niño-Southern Oscillation using sea surface salinity observations. J Geophys Res 116:C06016. doi:10.1029/2010JC006862 CrossRefGoogle Scholar
  50. Terray L, Corre L, Cravatte S, Delcroix T, Reverdin G, Ribes A (2012) Near-surface salinity as nature’s rain gauge to detect human influence on the tropical water cycle. J Clim 25(3):958–977CrossRefGoogle Scholar
  51. Thompson DWJ, Wallace JM, Jones PD, Kennedy JJ (2009) Identifying signatures of natural climate variability in time series of global-mean surface temperature: methodology and insights. J Clim 22(22):6120–6141. doi:10.1175/2009JCLI3089.1 CrossRefGoogle Scholar
  52. Timmermann A, Jin F (2002) A nonlinear mechanism for decadal El Niño amplitude changes. Geophys Res Lett 29(1):1003. doi:10.1029/2001GL013369 CrossRefGoogle Scholar
  53. Trenberth KE (1984) Signal versus noise in the southern oscillation. Mon Weather Rev 112:326–332CrossRefGoogle Scholar
  54. Trenberth KE, Hoar TJ (1996) The 1990–1995 El Niño-southern oscillation event: longest on record. Geophys Res Lett 23:57–60CrossRefGoogle Scholar
  55. Vincent DG (1994) The South Pacific Convergence Zone (SPCZ): a review. Mon Weather Rev 122:1949–1970CrossRefGoogle Scholar
  56. Wang B, An SI (2002) A mechanism for decadal changes of ENSO behavior: roles of background wind changes. Clim Dyn 18:475–486. doi:10.1007/s00382-001-0189-5 CrossRefGoogle Scholar
  57. Wu Z, Huang NE (2009) Ensemble empirical mode decomposition: a noise-assisted data analysis method. Adv Adapt Data Anal 1:1–41CrossRefGoogle Scholar
  58. Wu Z, Huang NE, Long SR, Peng CK (2007) On the trend, detrending, and the variability of nonlinear and nonstationary time series. Proc Natl Acad Sci U S A 104:14889–14894CrossRefGoogle Scholar
  59. Wu EKS, Kirtman BP, Sarachik ES, Huang NE, Tucker CJ (2008) The modulated annual cycle: an alternative reference frame for climate anomalies. Clim Dyn 31:823–841CrossRefGoogle Scholar

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

Personalised recommendations