[A-CG43] Multi-scale ocean-atmosphere interaction in the tropics

[ACG43-P05] Salinity-effect Strengthens ENSO Forced by Freshwater Flux Response to Global Warming in the Tropical Pacific

*Hai Zhi¹, Rong-Hua Zhang¹, Jiaxiang Gao¹ (1. Nanjing University of Information Science and Technology)

Keywords:Ocean salinity, Freshwater flux, Stratification , ENSO, Global warming

Human activities have caused marked global warming, which has in turn significantly intensified global water cycle and influenced ocean physics. However, a universally accepted understanding of how climate systems respond to freshwater flux (FWF) forcing under future warming remains elusive. This study investigates salinity change and its effect on ENSO in response of FWF forcing using the Flux-Anomaly-Forced Model Intercomparison Project (FAFMIP) experiments with the FGOALS-g3 model. Our findings reveal a 5.9% amplification in the spatial pattern of sea surface salinity (SSS) in the tropical Pacific due to FWF forcing. Notably, salinity decreases across the tropical Pacific, which enhances the east-west contrast of SSS and freshens the upper-ocean of the warm pool. These salinity changes lead to a shallower mixed layer, enhancing upper ocean stability. Moreover, changes in salinity variability modulate surface density, thereby influencing the mixing and the entrainment process at the base of mixing layer during ENSO, trapping more heat in the surface ocean. Consequently, our research suggests that FWF forcing could reduce the intensity of ENSO by 13% during cool ENSO and increase it by 23% during warm ENSO, enhances ENSO asymmetry by 30%. It is anticipated under future global warming, there be stronger El Niño and weaker La Niña events. The FAFMIP experiment provides valuable insights into how ocean salinity distribution responds to global warming when it is forced by FWF forcing, helping to improve ENSO forecast skills.