"The Arctic stratospheric ozone variations lead ENSO by 18–24 months, which means that it could be possible to extend the ENSO predictability from the current forecast level of several months up to around one and a half years in advance," Jianping Li of Beijing Normal University told environmentalresearchweb.

Earlier work looking for a lead-lag correlation between monthly Arctic stratospheric ozone and ENSO indices encouraged the researchers to investigate this link in more detail. They drew on both observations and simulations for the period 1980–2015.

In the current study in Environmental Research Letters, the scientists point to a range of processes driving the connection between Arctic stratospheric ozone and El Niño.

A negative anomaly in Arctic stratospheric ozone cools the stratosphere in the region, strengthening the stratospheric circulation. Then, over a period of around a month, the effect reaches the surface as a negative North Pacific oscillation anomaly.

In turn, this change in sea-level pressure initiates a positive Victoria Mode phase for the North Pacific. But when conditions are ripe, the positive Victoria Mode anomaly can influence the equatorial Pacific, strengthening an El Niño, the team found.

The whole process – featuring the high-latitude stratosphere to troposphere pathway and the extratropical to tropical climate teleconnection – was observed to take more than a year and a half from beginning to end.

As the researchers point out, the findings reinforce the need for climate models to include fully coupled stratospheric dynamical-radiative-chemical processes. And the group believes that such an update would allow more accurate simulation and prediction of ENSO variations.

"Our next steps are to further investigate the mechanism of Arctic stratospheric ozone affecting North Pacific sea surface temperature anomalies, as well as the long-range dependence and relevant oceanic processes of mid-latitude sea-surface temperature anomalies modulated by the Arctic stratospheric ozone," said Li. "This will help in building physically based empirical prediction models of ENSO using Arctic stratospheric ozone signals."

Other institutions participating in the study included Lanzhou University, the University of Washington, the University of Hawaii at Manoa, Peking University, Nanjing University and the Institute of Atmospheric Physics – Chinese Academy of Sciences.

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