El Ni\xf1o/Southern Oscillation inhibited by submesoscale ocean eddies

Shengpeng Wang,Bolan Gan,Zhaohui Chen,Lixin Wu,Wenju Cai,Haiyuan Yang,Xiaohui Ma,Hong Wang,Tao Geng,Zhao Jing,Gohkan Danabasoglu,Ping Chang

doi:10.1038/s41561-021-00890-2

Abstract

The El Niño/Southern Oscillation is characterized by irregular warm (El Niño) and cold (La Niña) events in the tropical Pacific Ocean, which have substantial global environmental and socioeconomic impacts. These events are generally attributed to the instability of basin-scale air–sea interactions in the equatorial Pacific. However, the role of sub-basin-scale processes in the El Niño/Southern Oscillation life cycle remains unknown due to the scarcity of observations and coarse resolution of climate models. Here, using a long-term high-resolution global climate simulation, we find that equatorial ocean eddies with horizontal wavelengths less than several hundred kilometres substantially inhibit the growth of La Niña and El Niño events. These submesoscale eddies are regulated by the intensity of Pacific cold-tongue temperature fronts. The eddies generate an anomalous surface cooling tendency during El Niño by inducing a reduced upward heat flux from the subsurface to the surface in the central-eastern equatorial Pacific; the opposite occurs during La Niña. This dampening effect is missing in the majority of state-of-the-art climate models. Our findings identify a pathway to resolve the long-standing overestimation of El Niño and La Niña amplitudes in climate simulations.

Highlights

As the most consequential mode of climate variability on our planet, the El Niño/Southern Oscillation (ENSO)[1,2] triggers a cascade of adverse impacts on ecosystems, agriculture and severe weather events around the world[3,4,5,6,7,8]
Equatorial mesoscale eddies, represented mainly by tropical instability waves (TIWs) and associated tropical instability vortices (TIVs) with horizontal wavelengths lying between 600 and 1,600 km, hinder ENSO growth through a lateral heat flux[25,26,27]
The impact of these submesoscale eddies on ENSO remains entirely unexplored and overlooked, probably because they are beyond the resolution capacity of existing observation systems and most state-of-the-art coupled global climate models (CGCMs)

Summary

Introduction

As the most consequential mode of climate variability on our planet, the El Niño/Southern Oscillation (ENSO)[1,2] triggers a cascade of adverse impacts on ecosystems, agriculture and severe weather events around the world[3,4,5,6,7,8]. We show an important role of submesoscale eddies in inhibiting ENSO growth and elucidate its underlying dynamics using an unprecedented long-term high-resolution CGCM simulation. Submesoscale eddies induce a pronounced climatological heat flux from the subsurface to the surface ocean, along the northern and southern edges of the cold tongue, with its intensity weakened and strengthened during El Niño and La Niña, respectively (Fig. 1e–g).

Results

Conclusion