Use of Footprint Modeling in a Regional Carbon Budget Approach to Estimate Gross Carbon Fluxes for Oregon-California: Component of ORCA and NACP-W

We present an approach to use footprint results simulated by the Stochastic Time-Inverted Lagrangian Transport (STILT) model in a project to determine the carbon balance of Oregon and northern California (ORCA project, see also Law et al., this meeting). ORCA provides a regional test of the overall NACP strategy by demonstrating bottom-up and model-data fusion approaches to derive carbon balances of a larger area. In this context, the STILT footprints, which identify the upstream influence area of atmospheric observations, will mainly be employed to increase the accuracy of the model-data fusion component (see also Styles et al., this meeting). The model-data fusion component focuses on the interpretation of daytime CO2 concentration drawdowns using a one-dimensional atmospheric boundary layer process model to infer CO2 fluxes. We employ STILT footprints to determine the relative influence of each part of the region surrounding the observation site on the measured concentration drawdown, and to identify the composition of landcover types within this area. The information on the contribution of fluxes emitted by the different landcover types to the CO2 drawdown is subsequently used to optimize base rates in the parameterization of process models for GPP, RA and RH. In addition to the application of STILT results for the optimization of the model-data fusion component, we present preliminary results of the comparison between the regional fluxes derived by bottom-up and model-data fusion approaches, respectively, under consideration of footprint results to ensure a consistent target area.