Simulation-driven analysis of airborne in-situ observations of natural methane emissions in northern Scandinavia

Abstract

Wetlands in the high northern latitudes are a major, yet poorly known contributor to the global methane budget. During the MAGIC-2021 campaign (Monitoring of Atmospheric composition and Greenhouse gases through multi-Instruments Campaigns), around 80 researchers collected greenhouse gas data in northern Scandinavia in August 2021. A variety of instruments were deployed on different platforms, including three research aircraft. Here we focus on airborne in-situ measurements with the DLR Cessna 208B Grand Caravan, which conducted 12 scientific flights in the region. The suite of instruments on board the aircraft provided methane mixing ratios, 3D wind, humidity, etc. along the flight track. Forward simulations with the MECO(n) model (MESSy-fied ECHAM and COSMO/MESSy models nested n times) support the interpretation of the measurements, e.g. to select cases dominated by local emissions for estimating methane emission fluxes from wetlands.

For a hindcast of MAGIC-2021, the meteorological conditions during the campaign period need to be reproduced as realistically as possible. Our MECO(2) setup uses a global EMAC instance with resolution T106 and two COSMO refinements with horizontal resolutions of 50 km and 7 km, respectively. EMAC ( ECHAM/MESSy Atmospheric Chemistry ) provides the boundary conditions for atmospheric dynamics and atmospheric composition for the first COSMO refinement. The S4D (Sampling in 4 Dimensions) module in MECO(n) allows output as line or curtain along the given flight track in the temporal resolution of the simulation time step, ensuring the best possible co-location with observations.

We run the global model with anthropogenic and natural emissions, and full atmospheric chemistry. The methane simulated in this way can be considered as background methane that is transported into the region of interest. In the regional model instances, a parameterised methane chemistry is considered, taking into account the loss of methane by oxidation with the hydroxyl radical. Additional diagnostic tracers focusing on the regional emissions from wetlands, lakes and soils are treated separately.

We discuss the simulations in the context of the analyses of the measurements and the challenges encountered in this case study.