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Simulation of salinity variability and the related freshwater flux forcing in the tropical Pacific: An evaluation using the Beijing normal university earth system model (BNU-ESM) |
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| Authors: | Hai Zhi Rong-Hua Zhang Pengfei Lin Lanning Wang |
| Institution: | 1. The Earth System Modeling Center and College of Atmospheric Sciences, Nanjing University of Information Science and Technology, Nanjing, 210044, China 2. Key Laboratory of Ocean Circulation and Waves, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, China 3. State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China 4. College of Global Change and Earth System Science, Beijing Normal University, Beijing, 100875, China |
| Abstract: | The climatology and interannual variability of sea surface salinity (SSS) and freshwater flux (FWF) in the equatorial Pacific are analyzed and evaluated using simulations from the Beijing Normal University Earth System Model (BNU-ESM). The simulated annual climatology and interannual variations of SSS, FWF, mixed layer depth (MLD), and buoyancy flux agree with those observed in the equatorial Pacific. The relationships among the interannual anomaly fields simulated by BNU-ESM are analyzed to illustrate the climate feedbacks induced by FWF in the tropical Pacific. The largest interannual variations of SSS and FWF are located in the western-central equatorial Pacific. A positive FWF feedback effect on sea surface temperature (SST) in the equatorial Pacific is identified. As a response to El Niño-Southern Oscillation (ENSO), the interannual variation of FWF induces ocean processes which, in turn, enhance ENSO. During El Niño, a positive FWF anomaly in the western-central Pacific (an indication of increased precipitation rates) acts to enhance a negative salinity anomaly and a negative surface ocean density anomaly, leading to stable stratification in the upper ocean. Hence, the vertical mixing and entrainment of subsurface water into the mixed layer are reduced, and the associated El Niño is enhanced. Related to this positive feedback, the simulated FWF bias is clearly reflected in SSS and SST simulations, with a positive FWF perturbation into the ocean corresponding to a low SSS and a small surface ocean density in the western-central equatorial Pacific warm pool. |
| Keywords: | freshwater flux salinity feedback tropical Pacific BNU-ESM |
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