Simplified aerosol modeling for variational data assimilation

[摘要] We have developed a simplified aerosol model together with its tangent linearand adjoint versions for the ultimate aim of optimizing global aerosol andaerosol precursor emission using variational data assimilation. The model wasderived from the general circulation model LMDz; it groups together the24 aerosol species simulated in LMDz into 4 species, namely gaseousprecursors, fine mode aerosols, coarse mode desert dust and coarse mode seasalt. The emissions have been kept as in the original model. Modifications,however, were introduced in the computation of aerosol optical depth and inthe processes of sedimentation, dry and wet deposition and sulphur chemistryto ensure consistency with the new set of species and their composition.

The simplified model successfully manages to reproduce the main features ofthe aerosol distribution in LMDz. The largest differences in aerosol load areobserved for fine mode aerosols and gaseous precursors. Differences betweenthe original and simplified models are mainly associated to the newdeposition and sedimentation velocities consistent with the definition ofspecies in the simplified model and the simplification of the sulphurchemistry. Furthermore, simulated aerosol optical depth remains within thevariability of monthly AERONET observations for all aerosol types and allsites throughout most of the year. Largest differences are observed oversites with strong desert dust influence. In terms of the daily aerosolvariability, the model is less able to reproduce the observed variabilityfrom the AERONET data with larger discrepancies in stations affected byindustrial aerosols. The simplified model however, closely follows the dailysimulation from LMDz.

Sensitivity analyses with the tangent linear version show that the simplifiedsulphur chemistry is the dominant process responsible for the strongnon-linearity of the model.

[学科分类] 天文学(综合)