24 Jun 2022
24 Jun 2022
Status: this preprint is currently under review for the journal ACP.

Driving mechanisms for the ENSO impact on stratospheric ozone

Samuel Benito-Barca, Natalia Calvo, and Marta Abalos Samuel Benito-Barca et al.
  • Earth Physics and Astrophysics Department, Universidad Complutense de Madrid, Madrid, Spain

Abstract. While the impact of El Niño-Southern Oscillation (ENSO) on the stratospheric circulation has been long recognized, its effects on stratospheric ozone have been less investigated. In particular, the impact on ozone of different ENSO flavors, Eastern Pacific (EP) El Niño and Central Pacific (CP) El Niño, as well as the driving mechanisms for the ozone variations have not been investigated to date. This study aims to explore these open questions by examining the anomalies in advective transport, mixing and chemistry associated with different El Niño flavors (EP and CP) and La Niña in the Northern Hemisphere in boreal winter. For this purpose, we use four 60-year ensemble members of the Whole Atmospheric Community Climate Model version 4. The results show a significant ENSO signal on total column ozone (TCO) during EP El Niño and La Niña events. During EP El Niño events, TCO is significantly reduced in the tropics and enhanced at middle and high latitudes in boreal winter. The opposite response has been found during La Niña. Interestingly, CP El Niño has no significant impact on extratropical TCO while its signal in the tropics is weaker than for EP El Niño events. The analysis of mechanisms reveals that advection through changes in tropical upwelling is the main driver for ozone variations in the lower tropical stratosphere, with a contribution of chemical processes above 30 hPa. At middle and high latitudes, stratospheric ozone variations related to ENSO result from combined changes in advection by residual circulation downwelling and changes in horizontal mixing linked to Rossby wave breaking and polar vortex anomalies. The impact of CP El Niño on the shallow branch of the residual circulation is small, and no significant impact is found on the deep branch.

Samuel Benito-Barca et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-378', John Albers, 20 Jul 2022
  • RC2: 'Comment on acp-2022-378', Peter Braesicke, 02 Sep 2022

Samuel Benito-Barca et al.

Samuel Benito-Barca et al.


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Short summary
The impact of different El Niño flavors (Eastern (EP) and Central (CP) Pacific El Niño) and La Niña on the stratospheric ozone is studied in a state-of-the-art chemistry-climate model. Ozone reduces in the tropics and increases in the extratropics when an EP El Niño event occurs, the opposite during La Niña. However, CP El Niño has no impact on extratropical ozone. These ozone variations are driven by changes in the stratospheric transport circulation, with an important contribution of mixing.