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Ultraviolet Radiation modelling using output from the Chemistry Climate Model Initiative

Kévin Lamy 1 Thierry Portafaix 1 Beatrice Josse 2 Colette Brogniez 3 Sophie Godin-Beekmann 4 Hassan Bencherif 1, 5 Laura Revell 6, 7, 8 Hideharu Akiyoshi 9 Slimane Bekki 4 Michaela Hegglin 10 Patrick Jöckel 11 Oliver Kirner 12 Virginie Marecal 2 Olaf Morgenstern 13 Andrea Stenke 6 Guang Zeng 13 N. Abraham 14, 15 Alexander Archibald 14 Neil Butchart 16 Martyn Chipperfield 17 Glauco Di Genova 18 Makoto Deushi 19 Sandip Dhomse 17 Rong-Ming Hu 4 Douglas Kinnison 20 Martine Michou 2 Fiona O'Connor 16 Luke Oman 21 Giovanni Pitari 18 David Plummer 22 John Pyle 14 Eugene Rozanov 23, 6 David Saint-Martin 2 Kengo Sudo 24 Taichu Tanaka 19 Daniele Visioni 18 Kohei Yoshida 19
Abstract : We have derived values of the Ultraviolet Index (UVI) at solar noon from the Tropospheric Ultraviolet Model (TUV) driven by ozone, temperature and aerosol fields from the first phase of the Chemistry-Climate Model Initiative (CCMI-1). Since clouds remain one of the largest uncertainties in climate projections, we simulated only clear-sky UVI. We compared the UVI climatologies obtained from CCMI and TUV against present-day climatological values of UVI derived from satellite data (the OMI-Aura OMUVBd product) and ground-based measurements (from the NDACC network). Depending on the region, relative differences between the UVI obtained from CCMI and TUV and ground-based measurements ranged between −4 % and 11 %. We calculated the UVI evolution throughout the 21st century for the four Representative Concentration Pathways (RCPs 2.6, 4.5, 6.0 and 8.5). Compared to 1960s values, we found an average increase in UVI in 2100 (of 2–4 %) in the tropical belt (30° N–30° S). For the mid-latitudes, we observed a 1.8 to 3.4 % increase in the Southern Hemisphere for RCP 2.6, 4.5 and 6.0, and found a 2.3 % decrease in RCP 8.5. Higher UV indices are projected in the Northern Hemisphere except for RCP 8.5. At high latitudes, ozone recovery is well identified and induces a complete return of mean UVI levels to 1960 values for RCP 8.5 in the Southern Hemisphere. In the Northern Hemisphere, UVI levels in 2100 are higher by 0.5 to 5.5 % for RCP 2.6, 4.5 and 6.0 and they are lower by 7.9 % for RCP 8.5. We analysed the impacts of greenhouse gases (GHGs) and ozone-depleting substances (ODSs) on UVI from 1960 by comparing CCMI sensitivity simulations (1960–2100) with fixed GHGs or ODSs at their respective 1960 levels. As expected with ODS fixed at their 1960 levels, there is no large decrease in ozone levels and consequently no sudden increase in UVI levels. With fixed GHG, we observed a delayed return of ozone to 1960 values, the same signal is observed on UVI, and looking at the UVI difference between 2090s values and 1960s values, we found an 8 % increase in the tropical belt during the summer of each hemisphere. Finally, we show that, while in the Southern Hemisphere UVI is mainly driven by total ozone column, in the Northern Hemisphere both total ozone column and aerosol optical depth drive UVI levels, with aerosol optical depth having twice as much influence on UVI as total column does.
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Kévin Lamy, Thierry Portafaix, Beatrice Josse, Colette Brogniez, Sophie Godin-Beekmann, et al.. Ultraviolet Radiation modelling using output from the Chemistry Climate Model Initiative. Atmospheric Chemistry and Physics Discussions, European Geosciences Union, 2018, ⟨10.5194/acp-2018-525⟩. ⟨insu-01813378⟩

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