Abstract
Abstract. We introduce a global-to-regional nesting scheme for atmospheric transport models used in simulating concentrations of green house gases from globally distributed surface fluxes. The coupled system of the regional Stochastic Time-Inverted Lagrangian Transport (STILT) model and the global atmospheric transport model (TM3) is designed to resolve atmospheric trace gas concentrations at high temporal and spatial resolutions in a specified domain e.g. for regional inverse applications. The nesting technique used for the coupling is based on a decomposition of the atmospheric concentration signal into a far-field and a near-field contribution enabling the usage of different model types for global (Eulerian) and regional (Lagrangian) scales. For illustrating the performance of the coupled TM3-STILT system we compare simulated mixing ratios of carbon dioxide with available observations at 10 sites in Europe. For all chosen sites the TM3-STILT provided higher correlations between the modelled and the measured time series than the TM3 global model. Autocorrelation analysis demonstrated that the TM3-STILT model captured temporal variability of measured tracer concentrations better than TM3 at most sites.
Highlights
Anthropogenic and biogenic emissions of trace gases at the surface cause large variations of atmospheric concentrations in the Planetary Boundary Layer (PBL), and upstream sources and sinks influence tracer mixing ratios at observational stations
Two domains were defined for the model simulations: the Global Domain (GD) with 72×48 grid cells on the spatial resolution of 4◦×5◦, and the regional domain of interest (DoI) covering central and western Europe from 12◦ W to 35◦ E and from 35◦ N and 62◦ N with 108×188 grid cells corresponding to a spatial resolution of 0.25◦×0.25◦ of the tracer flux field
The far-field part of the signal CFF is calculated by the global model in two steps as in the 2-step inversion scheme (Rodenbeck et al, 2009): 1. the global three-dimensional distribution of carbon dioxide mixing ratio in the atmosphere (Cglob) for GD/full period of simulations (FP) is calculated with the global TM3 model using an inversion-retrieved estimate of the carbon surface flux (Fposterior); 2. the near-field contribution in the global simulation is subtracted from the global CO2 field Cglob
Summary
Anthropogenic and biogenic emissions of trace gases at the surface cause large variations of atmospheric concentrations in the Planetary Boundary Layer (PBL), and upstream sources and sinks influence tracer mixing ratios at observational stations. The comparison against available observations is difficult and often requires averaging of the observed quantities in time and space to the model resolution Such averaging leads to a loss of information about fine scale signals that can be retrieved from trace gas fluxes at high temporal and spatial resolutions by an atmospheric inverse scheme (Lin and Gerbig, 2005; Gerbig et al, 2008). Trusilova et al.: A new coupled system for global-to-regional downscaling of CO2 only the model output at a limited number of available observation locations is required Such a local refinement of the spatial resolution for predicted variables may be achieved by using Lagrangian transport models (Rotach et al, 1996; Lin et al, 2003; Stohl et al, 2005; Pongratz et al, 2008) for calculating the footprint (near-field) and background (far-field) influences for each available observation. In this study we analyse the performance of the coupled system for the European domain and evaluate it against continuous measurements of CO2 concentrations at 10 European sites
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