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Asymmetry of Salinity Variability in the Tropical Pacific during Interdecadal Pacific Oscillation Phases

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Abstract

It has been recognized that salinity variability in the tropical Pacific is closely related to the Interdecadal Pacific Oscillation (IPO). Here, we use model simulations from 1900 to 2017 to illustrate obvious asymmetries of salinity variability in the tropical Pacific during positive and negative IPO phases. The amplitude of salinity variability in the tropical Pacific during positive IPO phases is larger than that during negative IPO phases, with a more westward shift of a large Sea Surface Salinity (SSS) anomaly along the equator. Salinity budget analyses show that the asymmetry of salinity variability during positive and negative IPO phases is dominated by the difference in the surface forcing associated with the freshwater flux [FWF, precipitation (P) minus evaporation (E)], with a contribution of 40%–50% near the dateline on the equator. Moreover, the relationships between the salinity variability and its budget terms also show differences in their lead-lag correlations during positive and negative IPO phases. These differences in salinity variability during different IPO phases produce asymmetric effects on seawater density which can reduce or enhance upper-ocean stratification. Therefore, the salinity effects may modulate the intensity of El Niño-Southern Oscillation (ENSO), resulting in an enhanced (reduced) El Niño but a reduced (enhanced) La Niña during positive (negative) IPO phases by 1.6°C psu−1 (1.3°C psu−1), respectively. It is suggested that the asymmetry of salinity variability may be related to the recent change in ENSO amplitude associated with the IPO, which can help elucidate ENSO diversity.

摘要

现有研究表明, 热带太平洋的盐度变化与太平洋年代际振荡 (IPO) 密切相关. 本文使用 1900 年至 2017 年的模式模拟 (LICOM3) 结果, 阐述了热带太平洋在正和负 IPO 相位期间盐度变化的不对称特性及机制. 分析发现热带太平洋在正 IPO 相位盐度变化强度大于负 IPO 期间, 且正 IPO 相位的海平面盐度异常沿赤道越向西扩展且增强越大. 盐度收支平衡分析表明, 在正和负 IPO 相位期间, 盐度变化的不对称性, 主要表现为与淡水通量 (FWF, 降水 (P) 减去蒸发 (E)) 相关的海表强迫差异, 淡水通量在赤道日期变更线附近对盐度异常的贡献为 40%–50%. 此外, 盐度变化与其收支项之间的关系还表现为它们在正和负 IPO 相位的超前-滞后相关性的差异. 因此, 不同 IPO 相位盐度变化的差异对海水密度具有不对称效应, 从而减弱或增强了上层海洋层结. 因此, 盐度效应可能会对 ENSO 的强度起到调节作用, 导致在正 (负) IPO 相位的 El Niño 增强 (减弱), La Niña 减弱 (增强). 盐度变化的不对称性可能与近期 ENSO 振幅的变化有关, 这项研究结果有助于阐明 ENSO 多样性.

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Acknowledgements

This research is supported by the National Natural Science Foundation of China (NSFC; Grant No. 42030410), the Laoshan Laboratory (Grant No. LSKJ202202403), and the National Key Research and Development Program on Monitoring, Early Warning and Prevention of Major Natural Disaster (Grant Nos. 2019YFC1510004, 2020YFA0608902). LIN is supported by the NSFC (Grant No. 41976026); ZHANG is additionally supported by the Startup Foundation for Introducing Talent of NUIST. We thank the Nanjing Hurricane Translation for reviewing the English language quality of this paper.

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Correspondence to Rong-Hua Zhang.

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Article Highlights

• The asymmetry of salinity interannual variability in the tropical Pacific is identified during positive and negative Interdecadal Pacific Oscillation (IPO) phases.

• The salinity asymmetry is mainly caused by the difference in the surface freshwater flux forcing, with its contribution reaching 40%–50% near the dateline.

• The related asymmetric salinity effects affect upper-ocean density and stratification, which can further modulate El Niño-Southern Oscillation (ENSO).

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Zhi, H., Yang, Z., Zhang, RH. et al. Asymmetry of Salinity Variability in the Tropical Pacific during Interdecadal Pacific Oscillation Phases. Adv. Atmos. Sci. 40, 1269–1284 (2023). https://doi.org/10.1007/s00376-022-2284-y

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  • DOI: https://doi.org/10.1007/s00376-022-2284-y

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