26 Apr 2022
26 Apr 2022
Status: this preprint is currently under review for the journal ACP.

Radiative impact of improved global parameterisations of oceanic dry deposition of ozone and lightning-generated NOx

Ashok K. Luhar, Ian E. Galbally, and Matthew T. Woodhouse Ashok K. Luhar et al.
  • CSIRO Oceans and Atmosphere, Aspendale, 3195, Australia

Abstract. We investigate the impact of recent process-based and empirical improvements to oceanic ozone dry deposition parameterisation and lightning-generated NOx (LNOx) parameterisation on radiative fluxes by conducting a 5-year simulation of the global ACCESS-UKCA chemistry-climate model with radiative feedbacks of ozone and methane included. Both parameterisations increase the global net downward top-of-the-atmosphere (TOA) radiative flux, akin to instantaneous radiative forcing, compared to the base parameterisations. The dry deposition improvement results in a relatively small increase of 4.3 mW m-2 in the net downward TOA radiative flux. But this increases to 86 mW m-2 when the improved LNOx parameterisation (which increases the LNOx production from 4.8 to 6.9 Tg N yr-1) is also used. For comparison, this estimated difference in the radiative flux is equivalent to ~18 % of the anthropogenic effective radiative forcing (ERF) due to ozone over the years 1750–2019 reported by the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (AR6). Other global changes from the use of the two parameterisations include an increase in the downward longwave radiation and a decrease in the downward shortwave radiation at the Earth’s surface, and a decrease of 0.64 years in the methane lifetime against loss due to the hydroxyl radical, with changes being larger in magnitude in the tropics. Although the total global LNOx production may be the same, how LNOx is distributed spatially makes a difference to radiative transfer. The changes in radiation components and methane lifetime per unit change in LNOx and column ozone are also calculated. We estimate that the uncertainty range in the net downward TOA radiation due to reported uncertainty range in global estimates of LNOx could be as much as 238 mW m-2. LNOx has a significant influence on the atmospheric lifetime of CH4, and the value of LNOx used within a model will influence the ERF and global warming potential of anthropogenic methane.

Ashok K. Luhar et al.

Status: open (until 18 Jun 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-275', Anonymous Referee #1, 19 May 2022 reply

Ashok K. Luhar et al.

Ashok K. Luhar et al.


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Short summary
This study shows that recent improvements to global parameterisations of oceanic ozone dry deposition and lightning-generated NOx (LNOx) impact Earth’s radiative fluxes. These radiation changes are larger in magnitude in the tropics and are dominated by the LNOx parameterisation change. Uncertainty in radiative fluxes arising from reported uncertainty in LNOx is estimated to be significant in comparison with the ‘present-day’ IPCC AR6 anthropogenic effective radiative forcing due to ozone.