Decadal modes of sea surface salinity and the water cycle in the tropical Pacific Ocean: The anomalous late 1990s |
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| Institution: | 1. Singapore-Delft Water Alliance, National University of Singapore, EW1-02-05, 2 Engineering Drive 2, Singapore 117577, Singapore;2. Department of Civil and Environmental Engineering, National University of Singapore, E1-08-24, 1 Engineering Drive 2, Singapore 117576, Singapore;3. Deltares, P.O. Box 177, 2600 MH Delft, The Netherlands;1. Wood Biology and Wood Products, Burckhardt Institute, Georg-August-University Göttingen, Büsgenweg 4, 37077 Göttingen, Germany;2. Technological Educational Institute of Thessaly, Department of Wood & Furniture Design and Technology, 431 00 Karditsa, Greece;1. Fudan University Shanghai Cancer Center, Fudan University, Shanghai 200025, PR China;2. Department of Oncology, Shanghai Medical College, Fudan University, Shanghai 200025, PR China;3. Department of Gastrointestinal Surgery, Shanghai Minimally Invasive Surgery Center, Ruijin Hospital, Shanghai Jiao Tong University, School of Medicine, Shanghai 20025, PR China;4. Department of Gastrointestinal Surgery, Tongji Hospital, Tongji Medical College in Huazhong University of Science and Technology, Wuhan, Hubei, PR China;1. School of Environment, Griffith University, Nathan, QLD 4111, Australia;2. School of Science, Nantong University, Nantong 226007, China;3. Bigelow Laboratory for Ocean Sciences, East Boothbay Harbor, ME 04544, USA;1. College of Life Science and Technology, Harbin Normal University, Harbin 150025, China;2. Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao 266003, China;3. Zoology Department, College of Science, King Saud University, Riyadh 11451, Saudi Arabia |
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| Abstract: | Limitations in sea surface salinity (SSS) observations and timescale separation methods have led to an incomplete picture of the mechanisms of SSS decadal variability in the tropical Pacific Ocean, where the El Niño Southern Oscillation (ENSO) dominates. Little is known regarding the roles of the North Pacific Gyre Oscillation (NPGO) and the Pacific Decadal Oscillation (PDO) in the large-scale SSS variability over the tropical basin. A self-organizing map (SOM) clustering analysis is performed on the intrinsic mode function (IMF) maps, which are decomposed from SSS and other hydrological fields by ensemble empirical mode decomposition (EEMD), to extract their asymmetric features on decadal timescales over the tropical Pacific. For SSS, an anomalous pattern appeared during 1997 to 2004, a period referred to as the anomalous late 1990s, when strong freshening prevailed in large areas over the southwestern basin and moderate salinization occurred in the western equatorial Pacific. During this period, the precipitation and surface currents were simultaneously subjected to anomalous fluctuations: the precipitation dipole and zonal current divergence along the equator coincided with the SSS increase in the far western equatorial Pacific, while the weak zonal current convergence in the southwestern basin and large-scale southward meridional currents tended to induce SSS decreases there. The dominant decadal modes of SSS and sea surface temperature (SST) in the tropical Pacific both resemble the NPGO but occur predominantly during the negative and positive NPGO phases, respectively. The similarities between the NPGO and Central Pacific ENSO (CP-ENSO) in their power spectra and associated spatial patterns in the tropics imply their dynamical links; the correspondence between the NPGO-like patterns during negative (positive) phases and the CP La Niña (CP El Niño) patterns for SSS is also discussed. |
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| Keywords: | Sea surface salinity Tropical Pacific Ocean Decadal variability North Pacific Gyre Oscillation Ensemble empirical mode decomposition Self-organizing map |
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