ENSO indices from sea surface salinity observed by Aquarius and Argo
- 470 Downloads
Analysis of the first 26 months of data from the Aquarius satellite confirms the existence of a sharp sea surface salinity (SSS) front along the equator in the western equatorial Pacific. Following several earlier studies, we use the longitudinal location of the 34.8-psu isohaline as an index, termed Niño-S34.8, to measure the zonal displacement of the SSS front and consequently the eastern edge of the western Pacific warm pool. The on-going collection of the Array for Real-time Geostrophic Oceanography (ARGO) program data shows high correlations between Niño-S34.8 and the existing indices of El Niño, suggesting its potential important role in ENSO evolution. Further analysis of the ARGO data reveals that SSS variability in the southeastern tropical Pacific is crucial to identify the type of El Niño. A new SSS index, termed the southeastern Pacific SSS index (SEPSI), is defined based on the SSS variability in the region (0°–10°S, 150°–90°W). The SEPSI is highly correlated with the El Niño Modoki index, as well as the Trans-Niño index, introduced by previous studies. It has large positive anomalies during central Pacific El Niño or El Niño Modoki events, as a result of enhanced zonal sea surface temperature gradients between the central and eastern tropical Pacific, and can be used to characterize the type of El Niño. The processes that possibly control these SSS indices are also discussed.
KeywordsSea surface salinity ENSO indices Equatorial Pacific Argo data Aquarius ocean salinity
- Kalnay E, Coauthors (1996) The NCEP/NCAR 40-year reanalysis project. Bull Am Meteorol Soc 77:437–371Google Scholar
- Lagerloef G, Coauthors (2013) Aquarius salinity validation analysis; data version 2.0. Aquarius project document, AQ-014-PS-0016, p 36Google Scholar
- 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 El Niño Southern Oscillation and biogeochemical phenomena. J Geophys Res 106:2363–2386. doi:10.1029/2000JC900141 CrossRefGoogle Scholar
- Qu T, Song YT, Maes C (2014) Sea surface salinity and barrier layer variability in the equatorial Pacific as seen from Aquarius and Argo. J Geophys Res 119. doi:10.1002/2013JC009375