Articles | Volume 18, issue 15
Atmos. Chem. Phys., 18, 11323–11343, 2018

Special issue: Chemistry–Climate Modelling Initiative (CCMI) (ACP/AMT/ESSD/GMD...

Atmos. Chem. Phys., 18, 11323–11343, 2018

Research article 13 Aug 2018

Research article | 13 Aug 2018

The representation of solar cycle signals in stratospheric ozone – Part 2: Analysis of global models

Amanda C. Maycock1, Katja Matthes2,3, Susann Tegtmeier2, Hauke Schmidt4, Rémi Thiéblemont5, Lon Hood6, Hideharu Akiyoshi7, Slimane Bekki5, Makoto Deushi8, Patrick Jöckel9, Oliver Kirner10, Markus Kunze11, Marion Marchand5, Daniel R. Marsh12, Martine Michou13, David Plummer14, Laura E. Revell15,16, Eugene Rozanov15,17, Andrea Stenke15, Yousuke Yamashita7,a, and Kohei Yoshida8 Amanda C. Maycock et al.
  • 1School of Earth and Environment, University of Leeds, Leeds, UK
  • 2GEOMAR Helmholtz for Ocean Research, Kiel, Germany
  • 3Christian-Albrechts-Universität zu Kiel, Kiel, Germany
  • 4Max Planck Institute for Meteorology, Hamburg, Germany
  • 5LATMOS, Institut Pierre Simon Laplace (IPSL), Paris, France
  • 6University of Arizona, Arizona, Tucson, USA
  • 7National Institute for Environmental Studies (NIES), Tsukuba, Japan
  • 8Meteorological Research Institute, Japan Meteorological Agency, Tsukuba, Japan
  • 9Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
  • 10Steinbuch Centre for Computing, Karlsruhe Institute of Technology, Karlsruhe, Germany
  • 11Institut für Meteorologie, Freie Universität Berlin, Berlin, Germany
  • 12National Center for Atmospheric Research, Boulder, Colorado USA
  • 13CNRM UMR 3589, Météo-France/CNRS, Toulouse, France
  • 14Environment and Climate Change Canada, Montreal, Canada
  • 15Institute for Atmospheric and Climate Science ETH, Zurich, Switzerland
  • 16Bodeker Scientific, Christchurch, New Zealand
  • 17Physikalisch-Meteorologisches Observatorium, World Radiation Center, Davos, Switzerland
  • anow at: Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama, Japan

Abstract. 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 (1–5 hPa) 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 0.55 K, 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.

Short summary
The 11-year solar cycle is an important driver of climate variability. Changes in incoming solar ultraviolet radiation affect atmospheric ozone, which in turn influences atmospheric temperatures. Constraining the impact of the solar cycle on ozone is therefore important for understanding climate variability. This study examines the representation of the solar influence on ozone in numerical models used to simulate past and future climate. We highlight important differences among model datasets.
Final-revised paper