Dipole Structure of Mixed Layer Salinity in Response to El Niño‐La Niña Asymmetry in the Tropical Pacific

Abstract

The asymmetry of mixed layer salinity (MLS) anomalies in response to El Niño and La Niña events in the tropical Pacific is examined for the first time based on Argo observations and Estimating the Circulation and Climate of the Ocean simulation. The difference of MLS anomalies between El Niño and La Niña shows a dipole structure, with El Niño featuring strong negative salinity anomalies east of 160°E while La Niña shows remarkable positive salinity anomalies west of 160°E. A salinity budget analysis suggests that nonlinear zonal advection plays a dominant role in generating the asymmetric MLS structure. This dipole MLS structure acts to generate a dipole structure of barrier layer thickness and thus likely plays an important role in the development of El Niño–Southern Oscillation asymmetries in sea surface temperature.

What Role Does the Barrier Layer Play During Extreme El Niño Events?

“…The data have a vertical resolution of ∼10–15 m in the upper 150 m and 25–30 m from 150–300 m. As discussed in Guan et al. (2019), the ECCO2 product has been applied in many scientific studies and has been validated with observations of oceanic circulation and water properties (e.g., Ponte & Vinogradova, 2016).…”

Zonal Structure of Tropical Pacific Surface Salinity Anomalies Affects ENSO Intensity and Asymmetry

“…For example, based on 17‐year Argo observational data set, Guan, Hu, et al. (2019, hereafter G2019) found maximum salinity anomalies appear in the central equatorial Pacific during El Niño, while they are located further west in the western equatorial Pacific during La Niña. They suggested that different zonal locations of salinity anomalies may have an impact on ENSO temperature asymmetry through affecting vertical density stratification.…”

Turbulent Mixing in the Barrier Layer of the Equatorial Pacific Ocean

“…Furthermore, the sustained shallow MLs favor enhanced and quick responses to wind (Maes et al., 2002; 2005). A particularly important dynamical consequence of BL is to modulate the development of El Niño (Corbett et al., 2017; Guan et al., 2019; Maes and Belamari, 2011; Maes et al., 2002; 2005; Qu et al., 2014; Zheng et al., 2014). Maes et al.…”