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.

[1] Climate models project an increase in the Brewer-Dobson circulation (BDC) with increasing future greenhouse gas (GHG) concentrations. This study identifies the causes of future changes in the BDC from sensitivity simulations with the EMAC chemistry-climate model, by changing the external forcings, like GHG concentrations, sea surface temperatures (SSTs) together with sea ice concentrations, and ozone-depleting substances (ODS), separately. The particular influence of rising tropical SSTs is assessed. Contributions of different waves to changes in the residual circulation are calculated as well as changes in mean age of stratospheric air (AoA) to account for the effect of mixing processes. We find that in boreal winter the tropical upward mass flux increases by about 1%/dec in the upper and 2%/dec in the lower stratosphere until the end of the 21 st century. Mean AoA decreases by up to 60 and 30 days/dec, respectively. Changes in transient planetary and synoptic waves account for the strengthening of the BDC in the lower stratosphere, whereas upper stratospheric changes are due to improved propagation properties for gravity waves in future climate. Regarding the external forcings, the radiative impact of rising GHG concentrations is detected to affect upper stratospheric layers only, whereas lower stratospheric signals are almost entirely due to rising SSTs. Changes in tropical SSTs influence not only the shallow but also the deep branch of the BDC as confirmed from both changes in residual circulation and mixing. Declining ODS will slightly counteract the BDC increase in the Southern Hemisphere.

The meridional circulation of the stratosphere, or Brewer‐Dobson circulation (BDC), is projected to accelerate with increasing greenhouse gas (GHG) concentrations. The acceleration is typically quantified by changes in the tropical upward mass flux (Ftrop) across a given pressure surface. Simultaneously, models project a lifting of the entire atmospheric circulation in response to GHGs; notably, the tropopause rises about a kilometer over this century. In this study, it is shown that most of the BDC trend is associated with the rise in the circulation. Using a chemistry‐climate model (CCM), Ftrop trends across 100 hPa are contrasted with those across the tropopause: while Ftrop at 100 hPa increases 1–2 %/decade, the mass flux entering the atmosphere above the tropopause actually decreases. Similar results are found for other CCMs, suggesting that changes in the BDC may better be described as an upward shift of the circulation, as opposed to an increase, with implications for the mechanism and stratosphere‐troposphere exchange.

Bromine from very short lived substances (VSLS), primarily from natural oceanic sources, contributes substantially to the stratospheric bromine loading. This source of stratospheric bromine has so far been ignored in most chemistry climate model calculations of stratospheric ozone trends. Here we present a transient simulation with the chemistry climate model EMAC for the period 1960–2005 including emissions of the five brominated VSLS CHBr3, CH2Br2, CH2BrCl, CHBrCl2, and CHBr2Cl. The emissions lead to a realistic stratospheric bromine loading of about 20 pptv for present‐day conditions. Comparison with a standard model simulation without VSLS shows large differences in modeled ozone in the extratropical lowermost stratosphere and in the troposphere. Differences in ozone maximize in the Antarctic Ozone Hole, resulting in more than 20% less ozone when VSLS are included. Even though the emissions of VSLS are assumed to be constant in time, the model simulation with VSLS included shows a much larger ozone decrease in the lowermost stratosphere during the 1979–1995 period and a faster ozone increase during 1996–2005, in better agreement with observed ozone trends than the standard simulation without VSLS emissions.

Using multidecadal simulations with the European Centre/Hamburg-Modular Earth Submodel System Atmospheric Chemistry (EMAC) model, the role of changing concentrations of ozone-depleting substances (ODSs) and greenhouse gases (GHGs) on Arctic springtime ozone was examined. The focus is on potential changes in the meteorological conditions relevant for Arctic ozone depletion. It is found that with rising GHG levels the lower Arctic stratosphere will cool significantly in early winter, while no significant temperature signal is identified later in winter or spring. A seasonal shift of the lowest polar minimum temperatures from late to early winter in the second part of the 21st century occurs. However, Arctic lower stratosphere temperatures do not seem to decline to new record minima. The future Arctic lower stratosphere vortex will have a longer lifetime, as a result of an earlier formation in autumn. No extended vortex persistence is found in spring due to enhanced dynamical warming by tropospheric wave forcing. Because of the dominant early winter cooling, largest accumulated polar stratospheric cloud (PSC) areas (A PSC ) are projected for the middle of the 21st century. A further increase of A PSC toward the end of the 21st century is prevented by increased dynamical polar warming. EMAC suggests that in the near future, there is a chance of low Arctic springtime ozone in individual years; however, there is no indication of a formation of regular Arctic ozone holes. Toward the end of the 21st century, when ODSs will be close to the 1960 levels, further rising GHG levels will cause increased Arctic springtime ozone.