Ground-based Validation Of Altitude, Temperature, And Four Primary Trace Gas Products Of The Operational MIPAS Level-2 Processors

Infrared observations at Earth's limb by the MIPAS instrument on Envisat has resulted in a unique data record to study physical and chemistry processes in the atmosphere. Profile retrievals are made of pressure, temperature and 15 trace gas species. The operational processor chain (Level-1b: IPF 7.11 + Level-2: ML2PP 7.03) recently completed the reprocessing of the entire MIPAS mission. This new version includes several significant improvements; we name just two. The non-linearity correction scheme in the Level-1 processor is now based on actual MIPAS observations, and the microwindow selection for Level-2 retrievals was reoptimized to improve the consistency between both parts of the MIPAS mission. Such changes potentially have an important impact on the quality of the Level-2 data products: their bias, precision or long-term stability, and their dependence on geophysical parameters. Here, we present the first consolidated results of the validation of five primary ML2PP 7.03 Level-2 data products (temperature, O3, HNO3, CH4 and N2O) and the altitude scale. Our analyses are based on comparisons to co-located ground-based observations by ozonesonde, stratospheric temperature and ozone lidar and FTIR instruments operating within the Network for the Detection of Atmospheric Composition Change (NDACC), WMO's Global Atmospheric Watch (GAW) and the Southern Hemisphere ADditional OZonesonde programme (SHADOZ). These networks provide well-characterized data records of different atmospheric constituents with appropriate accuracy and spatio-temporal sampling and resolution properties to act as a transfer standard for the validation of satellite data products. The considerable correlative statistics allowed an in-depth study of the structure of bias and short-term variability in the spatial (vertical, latitudinal) and temporal domain at various scales. In addition, it permitted us to characterize the quality of the different MIPAS spectral resolution modes and the different vertical sampling modes. For temperature, we show non-negligible changes in the long-term stability of ML2PP 7.03 relative to earlier MIPAS data versions (ML2PP 6.0 and IPF 5.05). We discuss whether this change also visibly affects the stability of other trace gas products (especially ozone). Another important topic is the consistency between MIPAS data from 2002-2004 and from 2005-2012, for all species. We conclude by showing that the ML2PP 7.03 altitude scale is superior to that reported in previous data releases.