Provision of near-real-time atmospheric CO2 concentrations in the MACC-II project: combining observations, land surface modelling, and high-resolution transport

The Monitoring Atmospheric Composition and Climate project (MACC-II) is the current pre-operational atmospheric service of the European GMES programme. MACC-II provides data records on atmospheric composition for recent years, data for monitoring present conditions and forecasts of the distribution of key constituents for a few days ahead. MACC combines state-of-the-art atmospheric modelling with Earth observation data to provide information services covering Air Quality and Atmospheric Composition, Climate Forcing, the Ozone Layer and UV radiation, Solar Energy, and Emissions and Surface Fluxes MACC-II uses a wide array of satellite and in-situ data observing both meteorological and atmospheric composition variables to provide a best estimate of the current state of the atmosphere on a daily basis. These analyses are then used as initial conditions for 5-day global forecasts of atmospheric composition and 4-day European air quality forecasts (http://www.gmes-atmosphere.eu). One of the aims of the MACC-II greenhouse gas service is to monitor fluxes of CO2 and CH4 using a combination of satellite and in-situ observations. However, a newly developed product is the provision of global atmospheric CO2 concentrations in near-real-time (NRT) that can be used as boundary conditions for regional studies as well as to monitor and support newly developed satellite observations, such as GOSAT and OCO-2. The system is able to produce various statistics about the behaviour of the satellite retrievals relative to the model. Also, the MACC-II system can provide accurate a priori information in NRT as input to these satellite retrievals. The CO2 forecasting system uses the ECMWF numerical weather prediction (NWP) model with a fully integrated version of the C-TESSEL land carbon model to model the net ecosystem exchange (NEE) fluxes over land. Anthropogenic emissions and ocean fluxes are currently prescribed, while the emissions from wild fires and biomass burning are provided by the NRT MACC-II Global Fire Assimilation System (GFAS). In order to avoid run-away biases in the global CO2 trend, the net ecosystem exchange (NEE) CO2 fluxes are re-scaled to constrain the atmospheric CO2 global growth based on past observations. We will present the newly-developed NRT CO2 forecasting system with all its components and explain the rationale behind it. The accuracy of the provided atmospheric CO2 fields will be shown by validating against surface based observations, including NRT ICOS observations and total column TCCON observations. Examples of how the output can be used to test and support satellite retrievals will form the final part of this presentation.