Methane and carbon dioxide fluxes and their regional scalability for the European Arctic wetlands during the MAMM project in summer 2012

Airborne and ground-based measurements of methane (CH₄), carbon dioxide (CO₂) and boundary layer thermodynamics were recorded over the Fennoscandian landscape (67-69.5° N, 20-28° E) in July 2012 as part of the MAMM (Methane and other greenhouse gases in the Arctic: Measurements, process studies and Modelling) field campaign. Employing these airborne measurements and a simple boundary layer box model, net regional-scale (∼ 100 km) fluxes were calculated to be 1.2 ± 0.5 mgCH₄ h^-1 m^-2 and -350 ± 143 mgCO₂ h^-1 m^-2 . These airborne fluxes were found to be relatively consistent with seasonally averaged surface chamber (1.3 ± 1.0 mgCH₄ h^-1 m^-2) and eddy covariance (1.3 ± 0.3 mgCH₄ h^-1 m^-2 and -309 ± 306 mgCO₂ h^-1 m^-2) flux measurements in the local area. The internal consistency of the aircraft-derived fluxes across a wide swath of Fennoscandia coupled with an excellent statistical comparison with local seasonally averaged ground-based measurements demonstrates the potential scalability of such localised measurements to regional-scale representativeness. Comparisons were also made to longerterm regional CH₄ climatologies from the JULES (Joint UK Land Environment Simulator) and HYBRID8 land surface models within the area of the MAMM campaign. The average hourly emission flux output for the summer period (July-August) for the year 2012 was 0.084 mgCH₄ h^-1 m^-2 (minimum 0.0 and maximum 0.21 mgCH₄ h^-1 m^-2) for the JULES model and 0.088 mgCH₄ h^-1 m^-2 (minimum 0.0008 and maximum 1.53 mgCH₄ h^-1 m^-2) for HYBRID8. Based on these observations both models were found to significantly underestimate the CH₄ emission flux in this region, which was linked to the under-prediction of the wetland extents generated by the models.