Level 2 processor and auxiliary data for ESA Version 8 final fullmission analysis of MIPAS measurements on ENVISAT

High quality long-term data sets of altitude-resolved measurements of the atmospheric composition areimportant because they can be used both to study the evolu-tion of the atmosphere and as a benchmark for future mis-sions. For the final ESA reprocessing of MIPAS (MichelsonInterferometer for Passive Atmospheric Sounding) on ENVISAT (ENViromental SATellite) data, numerous improve-ments were implemented in the Level 2 (L2) processor Op-timised Retrieval Model (ORM) version 8.22 (V8) and itsauxiliary data. The implemented changes involve all aspects of the processing chain, from the modelling of the measure-ments with the handling of the horizontal inhomogeneitiesalong the line of sight to the use of the optimal estimationtechnique to retrieve the minor species, from a more sensitive approach to detecting the spectra affected by cloudsto a refined method for identifying low quality products. Improvements in the modelling of the measurements werealso obtained with an update of the used spectroscopic dataand of the databases providing the a priori knowledge ofthe atmosphere. The HITRAN_mipas_pf4.45 spectroscopic database was finalised with new spectroscopic data verifiedwith MIPAS measurements themselves, while recently measured cross-sections were used for the heavy molecules. TheLevel 2 Initial Guess (IG2) data set, containing the clima-tology used by the MIPAS L2 processor to generate the ini-tial guess and interfering species profiles when the retrieved profiles from previous scans are not available, was improved taking into account the diurnal variation of the profiles defined using climatologies from both measurements and models. Horizontal gradients were generated using the ECMWFERA-Interim data closest in time and space to the MIPASdata. Further improvements in the L2 V8 products derivedfrom the use of the L1b V8 products, which were upgraded to reduce the instrumental temporal drift and to handle theabrupt changes in the calibration gain. The improvements in-troduced into the ORM V8 L2 processor and its upgraded auxiliary data, together with the use of the L1b V8 products, lead to the generation of the MIPAS L2 V8 products, which are characterised by an increased accuracy, better temporal stability and a greater number of retrieved species.