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

Abstract. Methane (CH₄) fluxes emitted by wetlands at high latitudes remain one of the largest sources of uncertainties in global methane budgets. At these latitudes, flux estimation approaches, such as atmospheric inversions, are impacted by improper characterisation of atmospheric transport due to challenging meteorological conditions and a lack of measurements. Here, we assess the performances of ERA5 reanalysis, mesoscale simulations from WRF-Chem, and various atmospheric transport models from several global and regional inversion systems using meteorological and CH₄ in-situ measurements collected during the MAGIC2021 campaign near Kiruna, Sweden. Over six measurements days in August 2021, ERA5 exhibited better agreement with observations than WRF-Chem thanks to data assimilation. Nevertheless, WRF-Chem demonstrated proficiency in simulating local atmospheric dynamics. Among global simulations of atmospheric concentrations of CH₄, inversion-optimised simulations of CH₄ concentrations yielded the best performances, particularly near the surface, with CAMS v21r1 marginally outperforming PYVAR-LMDz-SACS ensemble inversions. WRF-Chem regional simulations revealed performance disparities among CH₄ products, with positive biases in the boundary layer indicative of an overestimation of wetland emissions by selected wetland flux models. All transport models exhibited a vertically delayed gradient of CH₄ mixing ratios near the tropopause, resulting in a positive bias in the stratosphere. The high vertical resolution of CAMS hlkx facilitated a better representation of the vertical structure of CH₄ profiles in the stratosphere. Despite the limited spatiotemporal scope of MAGIC2021, we were able to identify the best performing transport models and to evaluate fluxes from different biogeochemical model parametrisations using the MAGIC2021 high-resolution dataset.