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

DATA ASSIMILATION FOR ATMOSPHERIC CHEMISTRY
In the regional version of MOCAGE-Valentina, we have performed several experiments assimilating surface
ozone measurement. The experiments also differ by the choice of the BECM configuration, in which
the correlations and standard deviations matrices come from the ensemble-based diagnostics or from a
posteriori diagnostics. All the analyses from these experiments are very well correlated to the observations,
what assimilated or validation stations. Comparisons of the analyses with the validation stations show that
the use of a BECM with time-dependent length-scales gives the largest correlation. All the analyses have a
better correlation with the observations than the direct MOCAGE simulation, but the differences between
them are small and we cannot conclude which BECM formulation is the most appropriate to the ozone
simulation over Europe. The impact of the BECM formulation has been also difficult to evaluate because
the model MOCAGE shows systematic bias in situation with low ozone concentration. So the impact of the
analysis process is mostly to remove this bias.
3.4 Development of linear chemistry schemes (S. Massart,
D. Cariolle J. Flemming)
During those past years a linearised ozone photochemical scheme has been developed for use within
GCMs and CTMs. This scheme is widely used for climate simulations and data assimilation studies. The
computational cost of this scheme is very low since it only requires an additional continuity equation to
be solved in the large scale models. We had therefore extended the methodology to treat other chemical
species, in particular a linearised scheme has been derived for CO and was implement in MOCAGE
[DA3, DA12, DA4]. CO is one of the most important tropospheric trace gases. In particular because it
affects the concentrations of the OH radical. Moreover the main sources of CO are incomplete fossil fuel
and biomass burning, which lead to enhanced surface concentrations. And with a lifetime of a few months
CO can serve as a tracer for regional and inter-continental transport of polluted air.
Within MACC a major development effort of the Global Reactive Gases sub-project is the on-line
integration of the chemistry in the IFS (known as C-IFS). C-IFS aims at a modular implementation of the
chemical scheme used in several global CTMs including MOCAGE. To complement the complex schemes,
linear scheme are explored in C-IFS for their potential in computational demanding application such as
high resolution simulations and data assimilation. So, in parallel with the comprehensive detailed chemical
schemes, we implemented in C-IFS the linearised parameterisation for CO.
(a) GEMS reanalysis
(b) High resolution simulation
FIG. 3.4: CO concentration (in ppbv) at 500 hPa for the 19 th January 2008.
82 Jan. 2010 – Dec. 2011