Abstract
Abstract. We have integrated the atmospheric chemistry and transport model TM5 into the global climate model EC-Earth version 2.4. We present an overview of the TM5 model and the two-way data exchange between TM5 and the IFS model from the European Centre for Medium-Range Weather Forecasts (ECMWF), the atmospheric general circulation model of EC-Earth. In this paper we evaluate the simulation of tropospheric chemistry and aerosols in a one-way coupled configuration. We have carried out a decadal simulation for present-day conditions and calculated chemical budgets and climatologies of tracer concentrations and aerosol optical depth. For comparison we have also performed offline simulations driven by meteorological fields from ECMWF's ERA-Interim reanalysis and output from the EC-Earth model itself. Compared to the offline simulations, the online-coupled system produces more efficient vertical mixing in the troposphere, which reflects an improvement of the treatment of cumulus convection. The chemistry in the EC-Earth simulations is affected by the fact that the current version of EC-Earth produces a cold bias with too dry air in large parts of the troposphere. Compared to the ERA-Interim driven simulation, the oxidizing capacity in EC-Earth is lower in the tropics and higher in the extratropics. The atmospheric lifetime of methane in EC-Earth is 9.4 years, which is 7% longer than the lifetime obtained with ERA-Interim but remains well within the range reported in the literature. We further evaluate the model by comparing the simulated climatologies of surface radon-222 and carbon monoxide, tropospheric and surface ozone, and aerosol optical depth against observational data. The work presented in this study is the first step in the development of EC-Earth into an Earth system model with fully interactive atmospheric chemistry and aerosols.
Highlights
Reactive gases and aerosols play important roles in the climate system
The system allows for two-way exchange of fields between Tracer Model 5 (TM5) and Integrated Forecasting System (IFS), the atmospheric general circulation models (GCMs) of EC-Earth
We have carried out a decadal simulation of tropospheric chemistry and aerosols for present-day conditions, and calculated chemical budgets and climatologies of tracer concentrations and aerosol optical depth
Summary
Reactive gases and aerosols play important roles in the climate system They affect the Earth’s energy balance by direct interaction with radiation and in various indirect ways. Despite the important role aerosols and chemically reactive gases play in the climate system, the description of atmospheric chemistry and aerosols varies strongly among climate models. The model allows for two-way exchange of fields between TM5 and IFS, but in this paper we focus on the impact of the online integration on the performance of TM5, without feedbacks to IFS To this end, we have carried out a decadal simulation of tropospheric chemistry and aerosols for present-day conditions, and calculated seasonal climatologies of concentration fields and chemical budgets for various tracers. We have extended the atmosphere–ocean GCM version of EC-Earth with a module for simulating atmospheric chemistry and transport, the Tracer Model 5 (TM5). We will give an overview of the main characteristics of this TM5 model version and briefly describe the most important modifications and improvements compared to these earlier publications
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