Scientific context

The first results from observational data of concentrations and isotopic abundance of CO2 in the atmosphere (Keeling, 1960) drew the attention to the large influence of antropogenic emissions of greenhouse gases in the industrial era on the global average mixing ratios of radiatively active greenhouse gases. Since these starting days a global observation network has grown that provided us with a view on the global annual growth rate and seasonal variability of CO2 and other greenhouse gases (Conway, 1994).
A big challenge is to develop the observational terrestrial network further to derive estimates of the fluxes of long lived greenhouse species on higher spatial and temporal resolution (independently checking the Kyoto protocol and beyond). Much progress has been made in the modelling arena using higher resolution transport models with or without coupled process based flux models (e.g. Bousquet, 2006). Using these models in inverse mode, usually in a Bayesian framework, will allow to derive improved estimates of fluxes or possibly even optimised parameters of the flux models from observations of fmixing ratios and/or fluxes from the network.
Besides transport and process models with high resolution in time and space this approach also requires the matching high resolution observational data of sufficient density and precision. In the past ten years an operational network has been developed in Europe, consisting of continuous sites employing a mixture of surface, tall tower and flux tower sites of excellent quality. However, this network has been developed for a range of purposes and using many different approaches.
In the current proposed Research Network TTORCH we will contribute to the further integration of this network to an observational system of higher consistency and even higher quality and precision, taking into account the developments in and around the evolving Integrated Carbon Observing System (ICOS). Some of the TTorch stations could become part of the ICOS Main Observation Sites, others could be part of an ICOS associated network or Regional Observation Site in the future.
The current network is focused mainly on Western Europe, but extension to the more Eastern part of Europe is needed. TTORCH will contribute to that in preparing and helping in building of the necessary infrastructure and to aid in the capacity building of (young) scientists in that part of Europe.
Focus of the current network of stations has been directed strongly to the Carbon cycle. The underlying infrastructure deployed is usually based on national initiatives and is kept alive with additional contributions from European projects from the different EU DG Research Framework Programmes. Large part of the Carbon cycle related work in observations and modelling is related to the CarboEurope cluster of projects (FP5) and CarboEurope IP (FP6, http://www.carboeurope.org). Additional greenhouse gas observations are often co-located with the Carbon cycle observations, but these observations generally are performed with lower resources, though the measurements and precision requirements are very demanding, and the running costs are high. A recent initiative directed to the non-CO2 greenhouse gases was the CHIOTTO project, in which 8 tall tower based observation sites were established (http://www.chiotto.org) for continuous high precision CO2, CH4, N2O, SF6 and CO observations.
Now that large part of the infrastructure for continuous surface base high precision measurements of non-CO2 greenhouse gases and related tracers is ready and delivering data series at this moment, there is at this moment due to a complexity of reasons and coincidences no overarching project or program to coordinate and use these measurements. TTORCH will try to provide some framework to keep the network and its consistency alive, even improve it where possible and prepare the extension to other parts of Europe. The partners of the TTORCH network will use the project as a platform for defining and building these new projects in cooperation with the research community.
The current European network forms an essential part of the Earth Observation network, with a relatively high density of the observations in Europe compared to most of the world. The surface based observations are now and will in the future be extended by using remote sensing data from for example satellites. However, by no means will remote sensing applications remove the need for surface observation in the near or even distant future because of the high accuracy and time resolution of the measurements, and the complementarity between ground based and satellite coverage.
Using point observations raises the problem of representativity of the measurements for the detection of larger scale processes. The basic idea is that long time series and continuous high precision measurements in combination with high resolution modelling will allow to use both the local and non-local information contained in the observed concentration and flux signals to derive fluxes representative for large areas.
Whether the existing network is of sufficient density to provide overlapping areas from which emission information can be obtained is a major question to be worked on, especially by the modelling community. Recent model studies suggest that observations in the temperate zone representative for the average PBL mixing ratios carry the flux information for areas up to at least 500 km distance from the observation point (Vermeulen, 2006;Bergamaschi, 2005).
As most of the EU FP6 projects dealing with non-CO2 greenhouse gas measurements and other relevant tracers and isotope ratio measurements have ended and support in the near future from FP7 or equivalent programs does not seem likely or take at least several years from now to even possibly start (e.g. ICOS initiative), these (non-)CO2 measurements are currently under severe threat. The TTORCH network will serve as a minimal option to keep the remains of the observational system coordinated, to help sustain the high quality where possible, and to start the capacity building to enable the future extension of the network in other parts of Europe.

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