CERFACS CERFACS Scientific Activity Report Jan. 2010 – Dec. 2011

3 Data assimilation for atmospheric
chemistry
The assimilation of minor atmospheric trace species is a very promising technique to obtain global and
regional datasets for the monitoring and the forecasting of the atmospheric composition. The challenge lies
in the optimal combination of measurements having very different resolutions in space and time, with for
examples in-situ data from ground-based stations, aircrafts, low Earth orbiting and geosynchronous satellite
measurements.
To combine all the measurement types within the models in an optimal manner using data assimilation
techniques, we have been developing and using at CERFACS for several years the data assimilation
suite built upon the Météo-France/CNRM chemistry transport model (CTM) MOCAGE. The develpment
started with the EC-FP5 ASSET European project in January 2003 in close collaboration with Météo-
France/CNRM. As the assimilation algorithm was developed under the CERFACS PALM (research)
environment, the resulting assimilation system was first called MOCAGE-PALM. But since the assimilation
modules are independent from the development of the PALM software and can be adapted to other models
than MOCAGE, we named later Valentina the reassembly of all the assimilation modules. This also
corresponded to the objectives of the ADOMOCA project of the PNCA (latter replaced by the LEFE
program) which promote Valentina as a common collaborative tool for the whole French community
involves in the ADOMOCA project. Starting in 2005, ADOMOCA made Valentina a more flexibility tool in
particular to be coupled with other models than MOCAGE (on regular or Gaussian global grid, on regional
grids, with various vertical grids and resolution) and to be able to assimilate a large range of atmospheric
composition data.
In parallel of the development work, we have improved Valentina in order to increase the quality of the
analysis it could provide. The most noticeable improvement came from the characterisation of the forecast
error and its model. This work was conducted in synergy with CERFACS assimilation studies in the
area of oceanography. To improve the analyses, several other directions were explored : four dimensional
assimilation method, a re-linearization iterative process and a control in the spectral space. Moreover, we
have developed linear chemical schemes for other species than ozone that prove to be very computationally
efficient for data assimilation.
Until recently, all scientific studies conduced with Valentina used MOCAGE in its global configuration.
But being involved in the regional cluster of the EC-FP7 MACC European project, we had to develop for
Météo-France/CNRM mi-2009 a system that is able to analyse daily ozone measurements from groundbased
station at the surface over Europe. The system was delivered to be operational mi-2010 with an
adapted version of Valentina able to assimilate data in the European domain of MOCAGE. Then we began
to conduce scientific studies with this new assimilation system.
3.1 Toward operational analyses and reanalyses of European air
quality (S. Massart, A. Piacentini, E. Jaumouillé)
Up to recently, the Valentina assimilation system has been involved in programs dealing with the global
atmospheric chemical composition, from the upper troposphere to the lower mesosphere. In the framework
of the EC-FP7 collaborative MACC project and the POGEQA (RTRA/STAE) national project, we had to
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