Study reveals how salinity affects El Ni帽o diversity
The El Ni帽o-Southern Oscillation (ENSO) is the strongest year-to-year climate variability in the planet, famous for prominent surface warming in the equatorial eastern Pacific known as an El Ni帽o event.
Recent decades have recognized weaker surface warming located more westward in some years, named as the central Pacific El Ni帽o (CPEN) in contrast to the traditional eastern Pacific El Ni帽o (EPEN). Previous studies have underscored various air-sea processes in shaping these differences, however, the impact of salinity remains unknown.
Recently, a research team led by Prof. Wang Fan from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) has revealed the dynamical mechanisms of ENSO diversity from the perspective of ocean salinity.
The study was published in on Oct. 31.
Based on Argo observations and reanalysis products, the researchers found maximum salinity anomalies during the two types of El Ni帽o showed clear different zonal structure, which occurred in the central equatorial Pacific (CEP) during the EPEN and in further western equatorial Pacific (WEP) during CPEN.
"Ocean salinity plays active roles in developing El Ni帽o warming through determining ocean vertical stratification and modifying the cooling entrainment and mixing from the subsurface, but we are curious about whether these different salinity zonal structures will affect the El Ni帽o diversity," said Dr. Guan Cong, first author of the study.
Based on ocean model experiments, the researchers found that salinity effect on El Ni帽o warming is very sensitive to zonal locations of salinity anomalies. The salinity anomalies located in the central Pacific are more effective in modulating local ocean vertical stratification, weakening the colder subsurface water into the mixed layer and further enhancing the surface warming.
Therefore, the central Pacific-located salinity anomalies during EPEN contributes to its stronger warming than those west-located salinity anomalies during CPEN, enhancing their sea surface temperature difference by 11%.
"Our results provide new insights in understanding the ENSO diversity and its low-frequency variability, which may be helpful for interpreting more complex model simulations and predicting ENSO variations," said Prof. Wang.
More information: Cong Guan et al, Zonal Structure of Tropical Pacific Surface Salinity Anomalies Affects the Eastern and Central Pacific El Ni帽os Differently, Geophysical Research Letters (2023).
Provided by Chinese Academy of Sciences
