Preprints
https://doi.org/10.5194/egusphere-2023-2618
https://doi.org/10.5194/egusphere-2023-2618
04 Dec 2023
 | 04 Dec 2023

Dynamical drivers of free-tropospheric ozone increases over equatorial Southeast Asia

Ryan M. Stauffer, Anne M. Thompson, Debra E. Kollonige, Ninong Komala, Habib Khirzin Al-Ghazali, Dian Yudha Risdianto, Ambun Dindang, Ahmad Fairudz bin Jamaluddin, Mohan Kumar Sammathuria, Norazura Binti Zakaria, Bryan J. Johnson, and Patrick D. Cullis

Abstract. Positive trends in tropical free-tropospheric (FT) ozone are frequently ascribed to emissions growth, but less is known about the effects of changing dynamics. Extending a prior study (Thompson et al., 2021; https://doi.org/10.1029/2021JD034691; “T21”), we re-examine Southern Hemisphere Additional Ozonesondes (SHADOZ) ozone trends over equatorial Southeast Asia (ESEA), one of Earth’s most convectively active regions, using 25 years (1998–2022) of ozone soundings. T21 posited that early-year positive FT ozone trends at equatorial SHADOZ stations are related to decreasing convection. The 25-year analysis of Kuala Lumpur and Watukosek SHADOZ records finds that +5 to +15 % (+2 to +6 nmol mol-1) per decade FT ozone trends from ~February–April coincide with large increases in satellite infrared brightness temperatures and outgoing longwave radiation, indicators of declining convective activity. MERRA-2 reanalyses exhibit decreases in upper tropospheric velocity potential and precipitable water, also indicating diminished convection. In contrast, trends in ozone and convective indicators are generally weak the rest of the year. These results suggest that decreases in convective intensity and frequency are primary drivers of FT ozone build-up over ESEA early in the year, i.e., waning convection suppresses lofting and dilution of ozone. Decreasing convection promotes accumulation of biomass burning emissions typical of boreal spring even though satellite FT carbon monoxide trends (2002–2022) over ESEA follow a global decrease pattern. Finally, our results demonstrate the advantages of monthly or seasonally resolved trends over annual means for robust attribution of observed ozone trends, challenging models to reproduce these detailed features in simulations of the past 25 years.

Ryan M. Stauffer, Anne M. Thompson, Debra E. Kollonige, Ninong Komala, Habib Khirzin Al-Ghazali, Dian Yudha Risdianto, Ambun Dindang, Ahmad Fairudz bin Jamaluddin, Mohan Kumar Sammathuria, Norazura Binti Zakaria, Bryan J. Johnson, and Patrick D. Cullis

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-2618', Anonymous Referee #1, 04 Jan 2024
  • RC2: 'Comment on egusphere-2023-2618', Anonymous Referee #2, 17 Jan 2024
  • CC1: 'Comment on egusphere-2023-2618', Owen Cooper, 19 Jan 2024
Ryan M. Stauffer, Anne M. Thompson, Debra E. Kollonige, Ninong Komala, Habib Khirzin Al-Ghazali, Dian Yudha Risdianto, Ambun Dindang, Ahmad Fairudz bin Jamaluddin, Mohan Kumar Sammathuria, Norazura Binti Zakaria, Bryan J. Johnson, and Patrick D. Cullis
Ryan M. Stauffer, Anne M. Thompson, Debra E. Kollonige, Ninong Komala, Habib Khirzin Al-Ghazali, Dian Yudha Risdianto, Ambun Dindang, Ahmad Fairudz bin Jamaluddin, Mohan Kumar Sammathuria, Norazura Binti Zakaria, Bryan J. Johnson, and Patrick D. Cullis

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Short summary
SHADOZ balloon-borne ozone measurements over equatorial Southeast Asia from 1998–2022 reveal that ozone increases during the early months of the year are linked to reduced convective storm activity, which typically redistributes and cleans the atmosphere of ozone. These findings challenge models to replicate the trends produced by the SHADOZ and meteorological observations and emphasizes the importance of studying monthly or seasonal, instead of annual changes for understanding ozone trends.