Sensitivities of simulated atmospheric CH4 concentrations in the ICON-ART Limited Area Mode

<p>We conducted CH<sub>4 </sub>simulations for Europe by using the ICON (<strong>ICO</strong>sahedral <strong>N</strong>on-hydrostatic)-ART (<strong>A</strong>erosols and <strong>R</strong>eactive <strong>T</strong>race gases) model and emissions from EDGAR.</p><p>With respect to the forecast of CH<sub>4</sub> in Limited Area Mode (Europe, 6.5 x 6.5 km), the model requires as accurate as possible initial and boundary atmospheric conditions. While the intial data denote here the state of the atmosphere 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 CH<sub>4 </sub>concentration data out side the domain.</p><p>The meteorological conditions can be obtained, for example,  from both the DWD's operational numerical weather prediction output or from Copernicus. The Copernicus Atmosphere Monitoring Service (CAMS) provides the necessary boundary CH<sub>4 </sub>data for the ICON-ART run in Limited Area Mode. The  CH<sub>4</sub> initial concentrations can be obtained from Copernicus or from a previous ICON-ART simulation run (e.g., the 24 h CH4 forecast from the previous day).</p><p>This way, ICON-ART in Limited Area Mode (LAM) allows for a flexible choice of boundary data and respective sensitivity testing. </p><p>To combine the meteorological data of the ICON with the CH<sub>4</sub> concentration data of CAMS as forcing data at the boundary, the CAMS data has to be provided on the same horizontal grid and the same vertical model levels as the ICON data. Since CAMS uses a vertical coordinate of a hybrid sigma-pressure system, the data has, in addition to the horizontal interpolation, to be interpolated vertically to the height based SLEVE coordinate system of ICON.</p><p>Also, the EDGAR emission datasets are interpolated to the target ICON grid. Both interpolations are characterized with respect introducing uncertainties.</p><p>Thirdly, variation in meteorological conditions is simulated by running ensembles in the ICON-ART LAM.</p><p>In this work, the ICON-ART CH<sub>4</sub> simulation setup forced by ICON meteorology and CAMS CH<sub>4</sub> boundary data is shown to be a useful method to simulate the CH<sub>4</sub> atmospheric concentrations at the regional scale and for the purposes of regional atmospheric inversions.</p><p>This work has been supported by the project Prototype system for a Copernicus CO<sub>2</sub> service (COCO2).</p><p> </p>