Reactive species from aviation in the multi-scale climate-chemistry model system MECO(n)
Authors: Matthes Sigrun , Peter Patrick , Kerkweg Astrid , Mertens Mariano , Jöckel Patrick , Zahn Andreas , Ziereis Helmut 
Published: December 2021

&lt;p&gt;Aviation aims to reduce its climate impact by identifying promising mitigation options which are able to reduce the overall climate effects of aviation considering CO&lt;sub&gt;2&lt;/sub&gt; and non-CO&lt;sub&gt;2&lt;/sub&gt; effects. While aiming to identify fuel optimal trajectories, aviation also aims to reduce the non-CO&lt;sub&gt;2&lt;/sub&gt; effects comprising NO&lt;sub&gt;x&lt;/sub&gt;-induced changes of atmospheric ozone and methane. Here climate-chemistry models are required which are able to quantify perturbations in atmospheric composition of reactive species (NO&lt;sub&gt;x&lt;/sub&gt;, O&lt;sub&gt;3&lt;/sub&gt;) and the associated radiative forcings of aviation emissions relying on advanced modelling capabilities, realistic emission inventory data and global-scale observational datasets from research infrastructures like IAGOS and DLR aircraft measurement campaign data.&lt;/p&gt;
&lt;p&gt;We use the multi-scale climate-chemistry MECO(n) system which is a &amp;#8220;MESSy-&amp;#64257;ed ECHAM and COSMO nested n-times&amp;#8221;, relying on the Modular Earth Submodel System (MESSy) framework. For this purpose, both models have been equipped with the MESSy infrastructure, implying that the same process formulations (MESSy submodels) are available for both models. Modelled atmospheric distributions are systematically compared to observational data from aircraft measurements in the upper troposphere and lower stratosphere. Nudging of meteorology to ERA5 interim data, and special diagnostics available within the modular MESSy infrastructure are implemented in the numerical simulations. Online sampling along aircraft trajectories allows to extract model data with a high temporal resolution (MESSy submodel S4D), in order to evaluate model representation and key processes.&lt;/p&gt;
&lt;p&gt;Beyond systematic evaluation with IAGOS scheduled aircraft measurements, episodes will be evaluated where dedicated measurements from aircraft campaigns are available, comprising Spring 2014 (ML-CIRRUS campaign), early summer 2020 (Blue Sky campaign) and summer 2021 (Cirrus-HL campaign). Our analysis of reactive species, NO&lt;sub&gt;y&lt;/sub&gt; and ozone, identifies those weather pattern and synoptic situations where aviation contributes strong signals, resulting in recommendations on measurement strategies to detect aviation signal in the atmosphere. We evaluate model representation of the NO&lt;sub&gt;x&lt;/sub&gt;-induces effect on radiatively active species ozone and methane in both model instances, ECHAM5 and COSMO. This is key for advancing the scientific understanding of NO&lt;sub&gt;x&lt;/sub&gt;-induced effects from aviation which is required in order to quantify potential compensation and trade-offs when identifying robust mitigation options for sustainable aviation.&lt;/p&gt;
&lt;p&gt;This project has received funding from the European Union&amp;#8217;s Horizon 2020 research and innovation programme under grant agreement No 875036 (ACACIA, Advancing the Science for Aviation and Climate) and has been supported by the DLR-Projekt Eco2Fly. This work uses measurement data from the European Research Infrastructure IAGOS/CARIBIC. High-Performance Super Computing simulations have been performed by the Deutsches Klima-Rechenzentrum (DKRZ, Hamburg) and the Leibniz-Rechenzentrum (LRZ, M&amp;#252;nchen).&lt;/p&gt;