Abstract. This paper describes the recommended solar forcing dataset for CMIP6 and highlights changes with respect to CMIP5. The solar forcing is provided for radiative properties, namely total solar irradiance (TSI), solar spectral irradiance (SSI), and the F10.7 index as well as particle forcing, including geomagnetic indices Ap and Kp, and ionization rates to account for effects of solar protons, electrons, and galactic cosmic rays. This is the first time that a recommendation for solar-driven particle forcing has been provided for a CMIP exercise. The solar forcing datasets are provided at daily and monthly resolution separately for the CMIP6 preindustrial control, historical (1850CMIP6 preindustrial control, historical ( -2014, and future (2015-2300) simulations. For the preindustrial control simulation, both constant and time-varying solar forcing components are provided, with the latter including variability on 11-year and shorter timescales but no long-term changes. For the future, we provide a realistic scenario of what solar behavior could be, as well as an additional extreme Maunderminimum-like sensitivity scenario. This paper describes the forcing datasets and also provides detailed recommendations as to their implementation in current climate models.For the historical simulations, the TSI and SSI time series are defined as the average of two solar irradiance models that are adapted to CMIP6 needs: an empirical onePublished by Copernicus Publications on behalf of the European Geosciences Union. A new and lower TSI value is recommended: the contemporary solar-cycle average is now 1361.0 W m −2 . The slight negative trend in TSI over the three most recent solar cycles in the CMIP6 dataset leads to only a small global radiative forcing of −0.04 W m −2 . In the 200-400 nm wavelength range, which is important for ozone photochemistry, the CMIP6 solar forcing dataset shows a larger solar-cycle variability contribution to TSI than in CMIP5 (50 % compared to 35 %).We compare the climatic effects of the CMIP6 solar forcing dataset to its CMIP5 predecessor by using timeslice experiments of two chemistry-climate models and a reference radiative transfer model. The differences in the long-term mean SSI in the CMIP6 dataset, compared to CMIP5, impact on climatological stratospheric conditions (lower shortwave heating rates of −0.35 K day −1 at the stratopause), cooler stratospheric temperatures (−1.5 K in the upper stratosphere), lower ozone abundances in the lower stratosphere (−3 %), and higher ozone abundances (+1.5 % in the upper stratosphere and lower mesosphere). Between the maximum and minimum phases of the 11-year solar cycle, there is an increase in shortwave heating rates (+0.2 K day −1 at the stratopause), temperatures (∼ 1 K at the stratopause), and ozone (+2.5 % in the upper stratosphere) in the tropical upper stratosphere using the CMIP6 forcing dataset. This solar-cycle response is slightly larger, but not statistically significantly different from that for the CMIP5 forcing dataset.CMIP6 models wi...

Abstract. Three types of reference simulations, as recommended by the Chemistry-Climate Model Initiative (CCMI), have been performed with version 2.51 of the European Centre for Medium-Range Weather Forecasts -Hamburg (ECHAM)/Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) model: hindcast simulations , hindcast simulations with specified dynamics , i.e. nudged towards ERA-Interim reanalysis data, and combined hindcast and projection simulations . The manuscript summarizes the updates of the model system and details the different model set-ups used, including the on-line calculated diagnostics. Simulations have been performed with two different nudging setups, with and without interactive tropospheric aerosol, and with and without a coupled ocean model. Two different vertical resolutions have been applied. The on-line calculated sources and sinks of reactive species are quantified and a first evaluation of the simulation results from a global perspective is provided as a quality check of the data. The focus is on the intercomparison of the different model set-ups. The simulation data will become publicly available via CCMI and the Climate and Environmental Retrieval and Archive (CERA) database of the German Climate Computing Centre (DKRZ). This manuscript is intended to serve as an extensive reference for further analyses of the Earth System Chemistry integrated Modelling (ESCiMo) simulations.

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[1] This study examines which part of the observed stratospheric thermal and dynamical changes since 1979 can be attributed to the observed stratospheric ozone (O 3 ) losses and CO 2 increases. Further, the processes are studied that lead to temperature and circulation changes when stratospheric O 3 and CO 2 are modified. We compared results from simulations of the Freie Universität Berlin Climate Middle Atmosphere Model (FUB CMAM) using observed O 3 and CO 2 changes with observed trends of stratospheric temperature and circulation for the period 1979-2000 from FUB data and National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalyses. The observed O 3 decrease leads in the FUB CMAM to a global mean stratospheric cooling, which is enhanced in the upper stratosphere by the imposed CO 2 increase. While the model is able to reproduce the observed stratospheric cooling in the upper stratosphere, it underestimates the observed trends in the lower stratosphere, particularly in middle latitudes and during Northern Hemisphere (NH) spring. The observed intensification and increased lifetimes of the polar vortices in spring are captured by the model but with smaller magnitude than observed. It is suggested that the observed upper stratospheric temperature trends during the past two decades in low to middle latitudes are caused by radiative effects due to the O 3 and CO 2 changes, while the cooling of the polar stratosphere in winter is enhanced by changes in dynamical heating. However, in northern midlatitudes and in Arctic spring, other effects than O 3 and CO 2 changes must be considered to fully explain the observed changes in the lower stratosphere.

[1] Using the equatorial electrojet (EEJ) peak current intensity as deduced from CHAMP magnetic observations from the years 2001 through 2009, we investigated the relationship between sudden stratospheric warming (SSW) and lunitidal signatures in the tropical ionosphere. There is a practically one-to-one correspondence between midwinter SSW periods and the strongest 13 day modulation of the EEJ strength as observed by CHAMP. That is, all the midwinter SSW periods from December 2001 to August 2009 were accompanied by an enhanced 13 day modulation of the EEJ strength. No other geophysical phenomenon brought about as strong a 13 day modulation as those of the midwinter SSW periods. During each midwinter SSW period the amplified 13 day modulation of the EEJ strengths starts roughly within AE1 week around the first peak in stratospheric temperature difference. An oscillation with a period of 13.26 days is predicted by the lunitidal equation when considering the precession of the CHAMP orbit. When fitting the lunitidal equation to the EEJ modulations during the midwinter SSW periods, consistent phase delays of 4.4 AE 0.3 days of the tidal signal emerge for all the cases. The results suggest that the pronounced 13 day modulation of the EEJ strength is related to an enhancement of the lunar tide in the ionosphere by the SSW effect.