Description: The impact of changes in incoming solar irradiance on stratospheric ozone abundances should be included in climate simulations to aid in capturing the atmospheric response to solar cycle variability. This study presents the first systematic comparison of the representation of the 11-year solar cycle ozone response (SOR) in chemistry–climate models (CCMs) and in pre-calculated ozone databases specified in climate models that do not include chemistry, with a special focus on comparing the recommended protocols for the Coupled Model Intercomparison Project Phase 5 and Phase 6 (CMIP5 and CMIP6). We analyse the SOR in eight CCMs from the Chemistry–Climate Model Initiative (CCMI-1) and compare these with results from three ozone databases for climate models: the Bodeker Scientific ozone database, the SPARC/Atmospheric Chemistry and Climate (AC&C) ozone database for CMIP5 and the SPARC/CCMI ozone database for CMIP6. The peak amplitude of the annual mean SOR in the tropical upper stratosphere (1–5hPa) decreases by more than a factor of 2, from around 5 to 2%, between the CMIP5 and CMIP6 ozone databases. This substantial decrease can be traced to the CMIP5 ozone database being constructed from a regression model fit to satellite and ozonesonde measurements, while the CMIP6 database is constructed from CCM simulations. The SOR in the CMIP6 ozone database therefore implicitly resembles the SOR in the CCMI-1 models. The structure in latitude of the SOR in the CMIP6 ozone database and CCMI-1 models is considerably smoother than in the CMIP5 database, which shows unrealistic sharp gradients in the SOR across the middle latitudes owing to the paucity of long-term ozone measurements in polar regions. The SORs in the CMIP6 ozone database and the CCMI-1 models show a seasonal dependence with enhanced meridional gradients at mid- to high latitudes in the winter hemisphere. The CMIP5 ozone database does not account for seasonal variations in the SOR, which is unrealistic. Sensitivity experiments with a global atmospheric model without chemistry (ECHAM6.3) are performed to assess the atmospheric impacts of changes in the representation of the SOR and solar spectral irradiance (SSI) forcing between CMIP5 and CMIP6. The larger amplitude of the SOR in the CMIP5 ozone database compared to CMIP6 causes a likely overestimation of the modelled tropical stratospheric temperature response between 11-year solar cycle minimum and maximum by up to 0.55K, or around 80% of the total amplitude. This effect is substantially larger than the change in temperature response due to differences in SSI forcing between CMIP5 and CMIP6. The results emphasize the importance of adequately representing the SOR in global models to capture the impact of the 11-year solar cycle on the atmosphere. Since a number of limitations in the representation of the SOR in the CMIP5 ozone database have been identified, we recommend that CMIP6 models without chemistry use the CMIP6 ozone database and the CMIP6 SSI dataset to better capture the climate impacts of solar variability. The SOR coefficients from the CMIP6 ozone database are published with this paper.

Description: We present the first high resolution measurements of pollutant trace gases in the Asian Summer Monsoon Upper Troposphere and Lowermost Stratosphere (UTLS) from the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) during the StratoClim (Stratospheric and upper tropospheric processes for better climate predictions) campaign with base in Kathamandu, Nepal, 2017. Measurements of peroxyacetyl nitrate (PAN), acetylene (C2H2), and formic acid (HCOOH) show strong local enhancements up to altitudes of 16 km. More than 500 pptv of PAN, more than 200 pptv of C2H2, and more than 200 pptv of HCOOH are observed. An observed local maximum of PAN and C2H2 at altitudes up to 18 km, reaching to the lowermost stratosphere, instead has been transported for a longer time. A local minimum of HCOOH is correlated with a maximum of ammonia (NH3), which suggests different wash out efficiencies of these species in the same air masses. To study the influence of convective transport to the measured pollution trace gas occurrences in detail, a trajectory analysis of the models ATLAS and TRACZILLA examined backward trajectories, starting at geolocations of GLORIA measurements with enhanced pollution trace gases. Both trajectory schemes implemented advanced techniques for detection of convective events. These convective events along trajectories leading to GLORIA measurements with enhanced pollutants are located close to regions, where satellite measurements by OMI show enhanced tropospheric columns of nitrogen dioxide (NO2) in the days prior to the observation. As an application of these highly resolved measurements, a comparison to the atmospheric models CAMS and EMAC is performed. It is demonstrated that these simulation results are able to reproduce large scale structures of the pollution trace gas distributions if the convective influence on the measured air masses is captured by the meteorological fields used by these simulations. Both models do not have sufficient horizontal resolution to capture all the convective events that are necessary to reproduce the fine structures measured by GLORIA. To investigate the influence of the strength of non-methane volatile organic compounds (NMVOCs) emissions in the EMAC model, sensitivity studies with artificially enhanced NMVOC emissions are performed. With these enhanced emissions, the simulation results succeed to reproduce the measured peak values of the pollutants, but do not improve the comparison of spatial distributions.