Evaluating Weather and Chemical Transport Models at High Latitudes using MAGIC2021 Airborne Measurements

Abstract. High latitude wetland emissions of methane (CH4) remain a significant source of uncertainty in global methane budgets. At these latitudes, flux estimation approaches, such as atmospheric inversions, are challenged by complex meteorological conditions, limited observational coverage, and uncertainties in atmospheric transport modelling. This study evaluates the performance of various atmospheric transport models and reanalysis datasets using meteorological and CH4 in-situ measurements collected during the MAGIC2021 campaign near Kiruna, Sweden. Over six days of measurements in August 2021, the ERA5 reanalysis, produced by the European Centre for Medium-Range Weather Forecasts (ECMWF) and providing global atmospheric data, showed better agreement with observations compared to the meso-scale Weather Research and Forecasting (WRF) model, though WRF provided valuable insights into local atmospheric dynamics. Among global simulations of CH4 mixing ratios, inversion-optimised models which adjust emissions to match observations, achieved the best performance overall particularly when constrained by surface measurements. Regional simulations from WRF coupled with chemistry (WRF-Chem) revealed biases in CH4 mixing ratios in the boundary layer, suggesting an overestimation of emissions by wetland models. All chemistry-transport models exhibited a positive bias in the stratosphere. Simulations with higher vertical resolution demonstrated an improved representation of vertical CH4 profiles in the upper layers of the atmosphere. Despite the limited spatio-temporal coverage of the observations, we were able to identify the best performing transport models and to evaluate fluxes from different biogeochemical model parameterisations using the MAGIC2021 high-resolution dataset, demonstrating the utility of in-situ vertical profile datasets for transport and flux model evaluation.