Park et al. (2025) Arctic stratospheric ozone as a precursor of ENSO events since 2000s

Identification

• Journal: npj Climate and Atmospheric Science
• Year: 2025
• Date: 2025-10-06
• Authors: Jae‐Heung Park, Ja‐Ho Koo, Jong‐Seong Kug, Su Jung Lee, Mi‐Kyung Sung, Joowan Kim, Eun‐Chul Chang, Young‐Min Yang, Sang Seo Park, Kyung‐Hwan Kwak, Ji‐Hoon Oh, Hongbo Kang, Soon‐Il An
• DOI: 10.1038/s41612-025-01220-8

Research Groups

• School of Earth and Environmental Sciences, Seoul National University, Seoul, South Korea
• Department of Atmospheric Sciences, Yonsei University, Seoul, South Korea
• Interdisciplinary Program in Artificial Intelligence, Seoul National University, Seoul, South Korea
• Korea Institute of Science and Technology, Seoul, South Korea
• Department of Atmospheric Science, Kongju National University, Gongju, South Korea
• Department of Environment & Energy, Jeonbuk National University, Jeonju-si, Jeollabuk-do, Republic of Korea
• School of Civil, Environmental, Resources and Energy Engineering, Jeonbuk National University, Jeonju-si, Jeollabuk-do, Republic of Korea
• Soil Environment Research Center, Jeonbuk National University, Jeonju-si, Jeollabuk-do, Republic of Korea
• Department of Civil Urban Earth and Environmental Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, South Korea
• School of Natural Resources and Environmental Science, Kangwon National University, Chuncheon, South Korea
• Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA

Short Summary

This study reveals a significant shift in the relationship between Arctic stratospheric ozone (ASO) and El Niño–Southern Oscillation (ENSO) since the 2000s, demonstrating that springtime ASO variations now serve as a precursor to subsequent winter ENSO events via a Eurasian teleconnection pathway.

Objective

• To revisit and understand the mechanism by which Arctic stratospheric ozone (ASO) influences the tropical Pacific, focusing on the period after the 2000s in the context of recent changes in the stratospheric polar vortex (SPV).

Study Configuration

• Spatial Scale: Arctic (70–90°N), Siberia (50–75°N, 70–130°E), tropical Pacific (5°S–5°N, 120–170°W for Niño3.4 index), global (reanalysis data). Vertical levels from 0.01 kPa to 85 kPa (0.01 hPa to 850 hPa).
• Temporal Scale: 1980–2023 (full analysis period), 2002–2023 (focus period for the new relationship), monthly, seasonal (springtime ASO, subsequent winter ENSO), with an approximate 8-month lag.

Methodology and Data

• Models used: Stationary Wave Model (SWM) – a nonlinear baroclinic model with 14 vertical sigma levels and rhomboidal 30 horizontal resolution.
• Data sources:
  • ECMWF Reanalysis Version 5 (ERA5)
  • Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA2)
  • Ozone Monitoring Instrument (OMI) OMTO3e dataset (Level-3 Aura/OMI product for total column ozone, 2005–2023, 0.25° latitude by 0.25° longitude spatial resolution).

Main Results

• The lead-lag relationship between ASO and ENSO shifted around the early 2000s. Before this period (1980-2001), ASO preceded ENSO with a negative correlation at approximately a 20-month lag. After the early 2000s (2002-2023), a positive ASO-preceding-ENSO signal emerged with an 8-month lag.
• Springtime (March–April) ASO variability is significantly correlated with subsequent winter (November–December) ENSO events, with a peak correlation coefficient of 0.63 when April ASO precedes November ENSO. The correlation between March-April ASO index and November-December ENSO index is 0.57 (ERA5) and 0.52 (OMI).
• The mechanism involves:
  1. Elevated springtime ASO, particularly over the Eurasian sector, due to the asymmetric structure of the Arctic stratospheric polar vortex (SPV) since the 2000s.
  2. Increased solar absorption by elevated ASO over Eurasia, leading to localized stratospheric heating (e.g., ~1 °C per 100 ppbm of ozone at 15 kPa).
  3. This heating induces an upper-tropospheric cyclonic circulation anomaly over Siberia.
  4. The cyclonic anomaly generates atmospheric waves that propagate southeastward, forming a wave train extending toward the tropical Pacific.
  5. Consequently, upper-level easterly and low-level westerly wind anomalies emerge over the equatorial Pacific, favoring El Niño development (or La Niña for decreased ASO).
• Changes in the SPV characteristics after the 2000s (weaker, more asymmetric, Eurasia-tilted) created favorable conditions for enhanced springtime ozone variability over Eurasia, facilitating this new ASO-ENSO correlation.

Contributions

• Identifies a previously undocumented shift in the ASO-ENSO relationship since the early 2000s, from a negative correlation with a 20-month lag (via North Pacific) to a positive correlation with an 8-month lag (via a Eurasian teleconnection pathway).
• Elucidates the chemical–radiative–dynamical processes in the Arctic stratosphere that link springtime ASO variability to subsequent winter ENSO events, highlighting the role of localized stratospheric heating over Eurasia.
• Demonstrates how changes in the Arctic stratospheric polar vortex structure since the 2000s have modulated the spatiotemporal distribution of ASO, thereby influencing tropospheric climate variability and ENSO development.

Funding

• National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (NRF-2023R1A2C1004083)
• NRF grant funded by the Korean government (MSIT) (RS-2023-00219830)
• NRF grant funded by the Korean government (NRF-2022R1A3B1077622)
• Korea Meteorological Administration Research and Development Program under Grant (RS-2025-02222417)
• Institute of Information & communications Technology Planning & Evaluation (IITP) grant funded by the Korean government (MSIT) [NO.RS-2021-II211343, Artificial Intelligence Graduate School Program (Seoul National University)]
• NRF grant funded by the Korean government (MSIT) (Grant No. RS-2024-00416848)
• Basic Science Research Program through the NRF funded by the Ministry of Education (RS-2025-02653909)

Citation

@article{Park2025Arctic,
  author = {Park, Jae‐Heung and Koo, Ja‐Ho and Kug, Jong‐Seong and Lee, Su Jung and Sung, Mi‐Kyung and Kim, Joowan and Chang, Eun‐Chul and Yang, Young‐Min and Park, Sang Seo and Kwak, Kyung‐Hwan and Oh, Ji‐Hoon and Kang, Hongbo and An, Soon‐Il},
  title = {Arctic stratospheric ozone as a precursor of ENSO events since 2000s},
  journal = {npj Climate and Atmospheric Science},
  year = {2025},
  doi = {10.1038/s41612-025-01220-8},
  url = {https://doi.org/10.1038/s41612-025-01220-8}
}