Improving global chemical simulations of the upper troposphere–lower stratosphere with sequential assimilation of MOZAIC data

The quantity and variety of atmospheric measurements of chemical constituents are strongly increasing, both for in situ and remote-sensing observing systems. This is an incentive to develop data assimilationschemes for atmospheric chemistry models, in the perspective of building realistic three-dimensionaltime-dependent distributions of observed and chemically related non-observed compounds. Sequentialdata assimilation experiments within the global Chemistry and Transport Model MOCAGE have beenconducted, in the perspective of using the MOZAIC database and meteorological analyses to drivea global simulation of ozone and related tracers, focussing specially on the upper troposphere—lowerstratosphere; the chemistry and dynamics in this region of the atmosphere are of great environmentalinterest, yet they are currently very difficult to model. Assimilation of subsonic flight-level observationsof ozone is anticipated to provide a significant contribution to improve numerical simulations. Resultsobtained with two different sequential data assimilation schemes are presented. The experiments havebeen set up on an 8-d period in February 1997. The “non-local” data assimilation technique appearspreferable to the “local” technique tested, since the benefits of assimilation for the former appear toremain for longer, possibly up to 3–4 d in the model integration after the data assimilation phase.