Strengthened Central Pacific ENSO Variability With Reduced Asymmetry Modulated by Upper‐Ocean Salinification Since the Late 1990s

Abstract Central Pacific (CP) El Niño‐Southern Oscillation (ENSO) variability has intensified since the late 1990s. Existing literature has emphasized the role of upper‐ocean stratification in modulating ENSO, primarily focusing on decadal thermal changes. This study further demonstrates that the regime shift of ENSO is modulated by the increasing salinity in the CP region. This decadal salinification enhances near‐surface density and weakens static stability, facilitating stronger vertical entrainment and a warmer subsurface at the base of the mixed layer. Consequently, thermocline feedback responsible for the growth of ENSO is reinforced during El Niño but weakened during La Niña, favoring stronger CP El Niño and weaker La Niña. Then the negative skewness of CP ENSO asymmetry is reduced. The CP salinification is primarily linked to a decadal intensification of the Walker circulation and reduced freshwater flux. Understanding these salinity‐driven processes is essential for improving ENSO predictions and mitigating climatic impacts on decadal‐to‐multidecadal timescales.