Objectives

The overall objective of ONC is to demonstrate the feasibility of monitoring vegetation-atmosphere CO2 exchange at the global scale, on daily to seasonal and inter-annual time scales. In situ meteorological measurements and different satellite remote sensing sources of information will be integrated by implementing and using assimilation techniques in global land surface models. At the end of the project ECMWF will be able to propose a near-operational system analysing land biospheric CO2 fluxes with a spatial resolution of about 50 km. Global or continental-scale land data assimilation systems (LDAS) have been developed in the last few years to characterise the surface energy and water budget, including changes in soil water and snow mass. The pioneering effort, coordinated by NASA, brings together a large community of meteorologists and hydrologists and runs currently in real-time, for the globe (GLDAS, at ¼ degree resolution) and North America (NLDAS, at 1/8 degree resolution). In Europe, ONC will provide a pre-operational global LDAS dealing with carbon accounting issues. Some ONC partners (ECMWF, KNMI, Météo-France, Alterra) are involved in the European LDAS (ELDAS) project which has created a daily data set spanning the year 2000 and the European continent. LDAS systems are able to collect all available remote sensing and in-situ information to create precipitation and surface radiative field, together with near-surface meteorology from atmospheric data assimilation centers. These fields are used to force state-of-the-art land-surface models, producing as output surface energy and water fluxes, soil water and snow mass. Uncertainty estimates can be obtained from varying the forcing and/or using different land-surface models. LDAS outputs document best estimates of the fields governing the surface-atmosphere interface; in particular, the soil moisture and snow mass fields can be used as initial conditions for weather prediction and monthly to seasonal forecasts.

So far, LDAS systems have not addressed carbon fluxes. However, a number of land surface models used in numerical weather prediction and climate studies now include photosynthesis and respiration modules coupled with biomass allocation schemes. For example, ISBA-A-gs at Météo-France (the French weather service) and ORCHIDEE at LSCE (a French research center of the Commissariat à l’Energie Atomique and of the Centre National de la Recherche Scientifique) are interactive vegetation models able to simulate the leaf area index and the vegetation biomass. Furthermore ORCHIDEE includes the slow carbon reservoirs of the soil and the dynamics of ecosystems after disturbance.

ONC will build on the modelling expertise of Météo-France and LSCE to implement a carbon LDAS at ECMWF.