Towards the assimilation of IASI Level 1 radiances for ozone and aerosols in a chemical transport model
Résumé
Level 2 (L2) retrievals from the Infrared Atmospheric Sounding Interferometer (IASI) have been used, for several years, to correct ozone (O3) analysis provided by chemical transport models (CTMs). This is achieved by means of data assimilation algorithms. However, the quality of the analysis might be influenced by the prior information used for the O3 retrievals. Another limitation is that desert dust aerosols have a significant influence in the region of the IASI spectrum used to retrieve ozone.
In this work, we evaluate the impact of assimilation of IASI Level 1 radiances including aerosols within the radiative transfer model on ozone analysis. Desert dust aerosols are, then, included in the control vector to assess the impact of coupled assimilation (ozone and aerosols) on their analyses.
We have computed hourly 3D-Var analyses assimilating L1 radiances from IASI in the chemical transport model MOCAGE. We have used a subset of 280 channels covering the spectral range between 980 and 1100 cm-1. The results are compared to independent data. The O3 fields are validated using ozonesondes and measurements from MLS (Microwave Limb Sounder). The impact on aerosols is evaluated using optical depth (AOD) from AERONET and MODIS (moderate-resolution Imaging Spectroradiometer).