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. The increasing availability of atmospheric measurements ofgreenhouse gases (GHGs) from surface stations can improve theretrieval of their fluxes at higher spatial and temporal resolutionsby inversions, provided that transport models are able to properlyrepresent the variability of concentrations observed at differentstations. South and East Asia (SEA; the study area in this paper including the regions ofSouth Asia and East Asia)is a region with large and veryuncertain emissions of carbon dioxide ( CO2 ) and methane( CH4 ), the most potent anthropogenic GHGs. Monitoringnetworks have expanded greatly during the past decade in thisregion, which should contribute to reducing uncertainties inestimates of regional GHG budgets. In this study, we simulateconcentrations of CH4 and CO2 using zoomed versions(abbreviated as “ZAs”) of the global chemistry transport modelLMDz-INCA, which have fine horizontal resolutions of ∼0.66 ∘ in longitude and ∼0.51 ∘ in latitudeover SEA and coarser resolutions elsewhere. The concentrations of CH4 and CO2 simulated from ZAs are compared to thosefrom the same model but with standard model grids of 2.50 ∘ in longitude and 1.27 ∘ in latitude (abbreviated as “STs”),both prescribed with the same natural and anthropogenicfluxes. Model performance is evaluated for each model version atmulti-annual, seasonal, synoptic and diurnal scales, againsta unique observation dataset including 39 global and regionalstations over SEA and around the world. Results show that ZAsimprove the overall representation of CH4 annual gradientsbetween stations in SEA, with reduction of RMSE by 16–20 %compared to STs. The model improvement mainly results from reductionin representation error at finer horizontal resolutions and thusbetter characterization of the CH4 concentration gradientsrelated to scattered distributed emission sources. However, theperformance of ZAs at a specific station as compared to STs is moresensitive to errors in meteorological forcings and surface fluxes,especially when short-term variabilities or stations close to sourceregions are examined. This highlights the importance of accuratea priori CH4 surface fluxes in high-resolution transportmodeling and inverse studies, particularly regarding locations andmagnitudes of emission hotspots. Model performance for CO2 suggests that the CO2 surface fluxes have not beenprescribed with sufficient accuracy and resolution, especially thespatiotemporally varying carbon exchange between land surface andatmosphere. In addition, the representation of the CH4 and CO2 short-term variabilities is also limited by model'sability to simulate boundary layer mixing and mesoscale transport incomplex terrains, emphasizing the need to improve sub-grid physicalparameterizations in addition to refinement of model resolutions.

atmospheric chemistry and physics

Simulating CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; and CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; over South and East Asia using the zoomed chemistry transport model LMDz-INCA