Simulation setup for atmospheric CH4 concentrations in the ICON-ART Limited Area Mode

An experimental setup within ICON (ICOsahedral Non-hydrostatic)-ART (Aerosols and Reactive Trace gases) has been  carried out to simulate the atmospheric CH4 concentration over Europe during the investigation period from 01 May 2018 to 30 June 2018.Modelling CH4 in the Limited Area Mode (Europe, 6.5 x 6.5 km), the model requires as accurate as possible initial and boundary atmospheric conditions as well as spatially highly resolved emissions. Temporal resolved emissions are to be included in the next step. While the intial data denote here the state of the atmosphere (meteorological and CH4 concentration fields) at the start of the model run, the boundary conditions shall denote the data in the lateral boundary zone where the model is forced by the meteorological and CH4 concentration data outside the domain. We have used DWD's operational numerical weather prediction output as meteorological boundary conditions. The Copernicus Atmosphere Monitoring Service (CAMS) provides the necessary initial and boundary CH4 data, which are made applicable  for the ICON-ART before the model run in Limited Area Mode. The regional CH4 emissions for Europe have been  provided by TNO and are processed with the ART module.  Since CAMS uses a vertical coordinate of a hybrid sigma-pressure system, the data had been horizontally and vertically interpolated to the height based SLEVE coordinate system of ICON. The sectorial CH4 emissions for Europe and for Germany were mapped separately to the target ICON grid by preprocessing the corresponding reported methane emissions of various sectors (resulting in 36 distinct methane variables in the model). The 50 largest point emissions from each sector are treated separately, smaller point emissions are treated together with the area emissions.To run a hourly experimental setup for two month the Basic Cycling environment (BACY) tool was used. The fields for meteorological parameters were initialized daily by using the DWD's operational data, while the atmospheric CH4 concentrations are taken from the previous ICON-ART CH4 simulation results (e.g., the 24 h CH4 forecast from the previous day). Then, the merged concentration fields for meterological conditions and atmospheric methane are used as “DWD first guess”, which served for a daily start of the simulation process in the ICON-ART Limited Area Mode. In order to compare the model results and measurements from the Integrated Carbon Observation System (ICOS) stations, the model equivalents have been extracted at the locations of the  ICOS montoring stations  using the “Model Equivalent Calculator”.In this work, the ICON-ART CH4 simulation setup for Limited Area Mode (Europe) was forced by ICON meteorology and CAMS CH4 boundary data and had been started daily by the merged “DWD first guess”. These are shown to be a useful method to simulate the CH4 atmospheric concentrations at the regional scale.