This study investigates the seasonal-to-interannual variability of the barrier layer (BL) associated with El Niño/Southern Oscillation (ENSO) using in situ temperature-salinity observations and simple ocean assimilation data (SODA). The comparisons with the BL derived from the in situ observations show that SODA successfully captures the variability of the BL in the Pacific warm pool. On seasonal timescale, based on the empirical orthogonal function (EOF) analysis, we identify that three seasonal leading modes of the BL along the equatorial Pacific are closely associated with the transition, resurgence and onset of ENSO, respectively. We also confirm that two interannual leading modes of the BL are related to different flavors of ENSO events. EOF1 mainly embodies a combined response to the central and east Pacific ENSO events while EOF2 is related to the central Pacific ENSO events. We especially focus on the contrast of the BL between east Pacific El Niño (EPEN) and central Pacific El Niño (CPEN). During EPEN, the abnormally thick BL appears in the east of the dateline. It follows the sea surface salinity front to shift zonally with the evolution of EPEN event, and propagates toward the central Pacific. It can be attributed to horizontal ocean advection, heavy precipitation and the downwelling Kelvin waves. In contrast, during CPEN, the abnormally thick BL is confined to the region between 160°E and 180°E around the SSS front without significant west–east displacement. It is mainly dominated by the local processes including Ekman pumping, precipitation, and zonal ocean advection. Different from the BL in the EPEN events, it has no evident basin-scale propagating signal.
Pacific warm pool Barrier layer Sea surface salinity El Niño/Southern Oscillation East Pacific El Niño Central Pacific El Niño
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This study is supported by the National Basic Research Program of China (2013CB430304), National Natural Science Foundation (41106005, 41176003, 41206178, 41376015, 41376013, and 41306006), National High-Tech R&D Program (2013AA09A505) of China, and Global Change and Air-Sea Interaction of China (GASI-IPOVAI-04, GASI-01-01-12).
Ando K, McPhaden MJ (1997) Variability of surface layer hydrography in the tropical Pacific Ocean. J Geophys Res 102:23063–23078CrossRefGoogle Scholar
Ashok K, Yamagata T (2009) Climate change: The El Niño with a difference. Nature 461:481–484CrossRefGoogle Scholar
de Boyer Montégut C, Mignot J, Lazar A, Cravatte S (2007) Control of salinity on the mixed layer depth in the world ocean: 1. General description. J Geophys Res 112:C06011. doi:10.1029/2006JC003953CrossRefGoogle Scholar
Kao HY, Yu JY (2009) Contrasting eastern Pacific and central Pacific types of ENSO. J Clim 22:615–632CrossRefGoogle Scholar
Kug JS, Jin FF, An SI (2009) Two types of El Niño events: cold tongue El Niño and warm pool El Niño. J Clim 22:1499–1515CrossRefGoogle Scholar
Lai AWC, Herzog M, Graf HF (2015) Two key parameters for the El niño continuum: zonal wind anomalies and Western Pacific subsurface potential temperature. Clim Dyn. doi:10.1007/s00382-015-2550-0Google Scholar
Larson S, Kirtman BP (2014) The Pacific meridional mode as an ENSO precursor and predictor in the North American multimodel ensemble. J Clim 27:7018–7032CrossRefGoogle Scholar
Maes C, Picaut J, Belamari S (2005) Importance of salinity barrier layer for the buildup of El Niño. J Clim 18:104–118CrossRefGoogle Scholar
Maes C, Ando K, Delcroix T, Kessler WS, McPhaden MJ, Roemmich D (2006) Observed correlation of surface salinity, temperature and barrier layer at the eastern edge of the western Pacific warm pool. Geophys Res Lett 33:L06601. doi:10.1029/2005GL024772CrossRefGoogle Scholar
Mignot J, de Boyer Montégut C, Lazar A, Cravatte S (2007) Control of salinity on the mixed layer depth in theworld ocean: 2. Tropical areas. J Geophys Res 112:C10010. doi:10.1029/2006JC003954CrossRefGoogle Scholar
Qu T, Song TY, Maes C (2014) Sea surface salinity and barrier layer variability in the equatorial Pacific as seen from Aquarius and Argo. J Geophys Res Oceans 119:15–29. doi:10.1002/2013JC009375CrossRefGoogle Scholar
Zheng F, Zhang RH, Zhu J (2014) Effects of interannual salinity variability on the barrier layer in the western-central equatorial Pacific: a diagnostic analysis from Argo. Adv Atmos Sci 31:532–542CrossRefGoogle Scholar