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

AVIATION AND ENVIRONMENT
of the scheme in terms of accuracy and shape preservation, which are important properties for the modelling
of atmospheric flows.
For example, Fig. 3.2 shows the result of a 2D advection for a Gaussian shape concentration distribution.
Winds were set as to create a vortex centered on the Equator. Each grid cell is represented as a single point
and colorised according to its concentration. We can see that the scheme preserve the filament shape, even
after several rotations.
FIG. 3.2: Evolution of a Gaussian concentration advected by vortex centred at the equator. Left : initial
state, middle : after 600 iterations, right : after 1000 iterations.
In this reduced grid, the address of neighbour cells are obtained by analytical formulas. This property will be
used for building a massively parallel code in Fortran 90 based on domain decomposition. For that purpose,
the grid will be partitioned at two levels. First, a three sectors division arises naturally when building the
grid. Then the remaining partitioning will be done according to the number of processors. The next steps
will be the introduction of a chemical scheme similar to the one used in chemical transport models in order
to study the scalability of the code for representative atmospheric situations.
3.3 Atmospheric impact of alternate fuel for aviation : the SWAFEA
project (D. Cariolle, R. Paoli)
Tropospheric ozone is a gas with a significant contribution to the greenhouse forcing, and is an oxidant that
can hump living species and human health at high concentrations. Ozone is formed in the troposphere via
several chemical cycles involving methane, NMH and VOC species and the nitrogen oxides. Consequently,
emissions of nitrogen oxides tend to increase the ozone formation. As such the aircraft NOx, CO and
NMH emissions contribute to the ozone production, especially at cruise altitude near the tropopause in the
northern hemisphere. Current evaluations report that about 7% of the ozone at the tropopause in the North
Atlantic corridor is due to the NOx injection by the current commercial fleet.
In the SWAFEA project CERFACS has investigated the possible impact of the use of alternate fuels on
the ozone formation. This has been done using the MOBIDIC 2D photochemical model using emissions
scenarios at the horizon 2026 constructed by AIRBUS based on gas emissions compiled by SAFRAN for
current and alternate jet fuels. The scenarios are based on traffic forecasts and evolution of the fleet, and are
constructed using the ELISA tool that combines air traffic data, fleet composition, distribution of routes,
and calculation of emissions along each mission.
The MOBIDIC model solves the transport-chemistry continuity equations as a function of latitude and
height. The chemistry scheme used in MOBIDIC includes the main gas-phase reactions driving the NOx,
HOx, ClOx, BrOx catalytic cycles, with 32 transported long-lived species, and 32 short-lived species
computed using steady-state assumptions. The gas-phase chemical rates have been upgraded according to
the recommendations of the JPL-2003-25 report. For the present study the chemical scheme of MOBIDIC
CERFACS ACTIVITY REPORT 189