Abstract
Four cross-coupled models were used to investigate the relative contributions of atmospheric and oceanic components to the asymmetry of the El Niño–Southern Oscillation (ENSO). Strong El Niño and La Niña events related to the negative heat flux feedbacks were found to be determined mainly by the atmospheric component, and the stronger sea surface temperature (SST) anomalies in the warm phase did not lead to an increased SST asymmetry. The skewness of the four models could be affected by both atmospheric and oceanic components; the atmospheric component determines the strength of positive and negative SST anomalies, and the oceanic component affects the strength of the negative SST anomalies in the cold phase under the same atmospheric component group. The Bjerknes stability index (BJ index) of warm and cold phases contributed to the El Niño–La Niña SSTA asymmetries in observation, but the BJ index did not necessarily explain the El Niño–La Niña SSTA asymmetries in climate model simulations. The SST asymmetries in these four models were closely associated with convective precipitation and wind stress asymmetries, which are also determined by both the atmospheric and oceanic components.
Highlights
The El Niño–Southern Oscillation (ENSO) is characterized as a sea surface temperature anomaly in the central-eastern equatorial Pacific that occurs every 2–7 years with considerable irregularity in amplitude, duration, and temporal evolution [1]
An et al [5] found that, during the development of strong El Niño, the enhancement of the vertical advection induces the anomalous warm water in the subsurface to upwell to the surface layer, which results in a nonlinear acceleration of surface warming, whereas during the transition to La Niña, there is an anomalous downwelling caused by the westerly wind anomalies, which results in the slowdown of the surface cooling
Community Earth System Model (CESM) showed the strongest skewness that was comparable with the observations in all four time slices, whereas the other three models all underestimated the asymmetry, and the value of FGOALS-g2 was uniformly negative
Summary
The El Niño–Southern Oscillation (ENSO) is characterized as a sea surface temperature anomaly in the central-eastern equatorial Pacific that occurs every 2–7 years with considerable irregularity in amplitude, duration, and temporal evolution [1]. An et al [5] found that, during the development of strong El Niño, the enhancement of the vertical advection induces the anomalous warm water in the subsurface to upwell to the surface layer, which results in a nonlinear acceleration of surface warming, whereas during the transition to La Niña, there is an anomalous downwelling caused by the westerly wind anomalies, which results in the slowdown of the surface cooling. Reanalysis and indicated that the linear advection term leads to the symmetry of warm and cold phases, whereas the nonlinear advection tends to enhance El Niño but weaken La Niña and is responsible for the amplitude asymmetry. The results of modeling and observations/reanalysis described above demonstrated that both atmospheric and oceanic processes can cause the ENSO asymmetry. Version 2; FGOALS-g2), CESM-g2, and FGOALS-c4 [13,14]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
