## 3 Earth Surface Modelling Advances and Links with EO Datasets
### Land-Atmosphere Fluxes
#### 3.2.1 Co\({}_{2}\) Natural Ecosystem Exchange
The operational CAMS (Copernicus Atmosphere Monitoring Service) atmospheric CO\({}_{2}\) analysis and forecast system has been using the online NEE fluxes from CH-TESSEL ever since its introduction in the IFS, replacing the offline CASA fluxes from the GFED dataset [151]. Extensive testing of this online configuration shows that the global CO\({}_{2}\) atmospheric inter-annual variability is well simulated [152]. The correlation of global CO\({}_{2}\) with observationally based estimates is 0.70. The global CO\({}_{2}\) forecast has high skill in simulating day-to-day synoptic variability, which is crucial in order to be able to assimilate atmospheric CO\({}_{2}\) observations. Figure 13 illustrates the spatial and temporal CO\({}_{2}\) synoptic anomalies associated with the passage of synoptic weather systems over North America. The CO\({}_{2}\) forecast can represent the peaks of CO  
Figure 13: Atmospheric CO\({}_{2}\) anomalies associated with the passage of a low pressure system over N. America: (**a**) CO\({}_{2}\) anomalies above the well-mixed background CO\({}_{2}\) at different levels in the vertical: grey near the surface, cyan at 850 hPa, blue at 500 hPa and dark grey at 300 hPa on 24 September 2010. The anomalies are defined as CO\({}_{2}\) dry molar fraction above the background value of 392 ppm for both near the surface and at the 850 hPa levels, and above the background value of 388 for the 500 and 300 hPa levels. The locations of the observing site of the Park Falls Tower (Wisconsin, USA) is depicted by a red triangle. The black contours of mean sea level pressure show the location of the centre of low pressure systems; (**b**) daily mean dry molar fraction (ppm) of CO\({}_{2}\) from measurements (black) and forecasts (cyan) at Park Falls in September 2010. The observations are courtesy of NOAA Earth System Research Laboratory [150]. observed at Park Falls (Wisconsin, USA) originating mainly from the advection of high CO\({}_{2}\) anomalies generated at the surface within the warm conveyor belt of synoptic low-pressure systems. Modelling day-to-day variability of the CO\({}_{2}\) fluxes from vegetation compared to using equivalent monthly mean fluxes with a diurnal cycle enhances significantly the atmospheric CO\({}_{2}\) variability and skill. Again, this illustrates the advantage of modelling the CO\({}_{2}\) fluxes inside the IFS with real-time meteorology. Despite the synoptic skill provided by the NEE synoptic variability, the model suffers from substantial biases in the biogenic CO\({}_{2}\) fluxes (GPP and Reco). These biases are diagnosed and corrected by comparing the model budget with a reference budget from a flux inversion system [153] based on in situ observations of atmospheric CO\({}_{2}\) at the surface [154]. The biogenic flux adjustment scheme of [153] addresses the important task of reconciling the bottom-up and top-down estimates of CO\({}_{2}\) fluxes. The benefits are a substantial reduction in the atmospheric CO\({}_{2}\) biases as well as a useful diagnostic to guide model developement. New data sets based on FLUXNET data [155] or satellite observations of Solar Induced Chlorophyll Fluorescence [156] can also be used to improve the attribution of the errors associated with GPP and Reco.