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 assimilation schemes for atmospheric chemistry models, in the perspective of building realistic three-dimensional time-dependent distributions of observed and chemically related non-observed compounds. Sequential data assimilation experiments within the global Chemistry and Transport Model MOCAGE have been conducted, in the perspective of using the MOZAIC database and meteorological analyses to drive a global simulation of ozone and related tracers, focussing specially on the upper troposphere–lower stratosphere; the chemistry and dynamics in this region of the atmosphere are of great environmental interest, yet they are currently very difficult to model. Assimilation of subsonic flight-level observations of ozone is anticipated to provide a significant contribution to improve numerical simulations. Results obtained with two different sequential data assimilation schemes are presented. The experiments have been set up on an 8-d period in February 1997. The "non-local" data assimilation technique appears preferable to the "local" technique tested, since the benefits of assimilation for the former appear to remain for longer, possibly up to 3–4 d in the model integration after the data assimilation phase.