The influence of using ERA-5 instead of ERA-Interim on stratospheric chemistry and ozone in EMAC simulations

In 2019, the European Centre for Medium-Range Weather Forecasts (ECMWF) published the ERA-5 reanalysis dataset (Hersbach et al., 2020). These new reanalysis data set replaced ERA-Interim (Dee at al., 2011), which had been previously often used in nudged simulations.

ERA-5 provides hourly estimates of a large number of atmospheric, land and oceanic climate variables. It uses a horizontal resolution of T639 (approx. 31km) and resolves the atmosphere using 137 levels from the surface up to a height of 1 Pa (approx. 80km). ERA-Interim only used T255 (approx. 79 km) with 60 levels from the surface up to 10 Pa (approx. 60 km) with a 6-hourly output.

To investigate the impact of these two reanalyses on the results of chemistry-climate simulations with the ECHAM/MESSy Atmospheric Chemistry (EMAC) model system, we performed three nudged simulations from 1979 to present.

EMAC is a numerical chemistry and climate simulation system that includes submodels describing tropospheric and middle-atmospheric processes and their interaction with oceans, land and human influences (Jöckel et al., 2010). We used EMAC (ECHAM5 version 5.3.02, MESSy version 2.55) with a horizontal resolution of T42 (corresponding to a quadratic Gaussian grid of 2.8° x 2.8°) and with 90 levels up to 0.01 hPa (approx. 80 km). The applied model setup includes a comprehensive chemistry scheme with gas-phase reactions and heterogeneous reactions on polar stratospheric clouds (PSCs). We used a similar setup as in the REF-D1 simulations for the IGAC/SPARC Chemistry-Climate Model Initiative (CCMI) using boundary conditions for greenhouse gases from CMIP-6 (Eyring et al., 2016) and for ozone depleting substances mainly from WMO (2008). Surface pressure, temperature, vorticity and divergence were nudged above the boundary layer and below 1 hPa (approx. 50 km) using a Newtonian relaxation technique.

We performed three EMAC simulations all with the same model setup as described above, but used as reanalysis data set ERA-Interim in the first simulation (from 1979 to 201908), and ERA-5 in the second and third simulation (from 1979 to 2021). In the third simulation we used from 2000 to 2006 the ERA-5.1 data set instead of the ERA-5. ERA-5.1 is a rerun of ERA5 for the years 2000 to 2006 only, in which the cold bias in the lower stratosphere seen in ERA5 was improved.

In our presentation, we will compare these three EMAC simulations regarding temperature, dynamic and chemistry with focus of the influence of the different reanalysis data sets to the distribution and development of stratospheric ozone.

Additional we will present the comparisons of ozone fields of our three simulations with different satellite observations (in particular MIPAS and MLS) and access whether the use of ERA-5 leads to an improvement of the results of our EMAC simulations.