The ESA MIPAS/Envisat level2-v8 dataset: 10 years of measurements retrieved with ORM v8.22
Authors: Dinelli Bianca Maria , Raspollini Piera , Gai Marco , Sgheri Luca , Ridolfi Marco , Ceccherini Simone , Barbara Flavio , Zoppetti Nicola , Castelli Elisa , Papandrea Enzo , Pettinari Paolo , Dehn Angelika , Dudhia Anu , Kiefer Michael , Piro Alessandro , Flaud Jean-Marie , López-Puertas Manuel , Moore David , Remedios John , Bianchini Massimo 
Published: December 2021

Abstract. The observations acquired during the full mission of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument, aboard the European Space Agency Environmental Satellite (Envisat), have been analysed with version 8.22 of the Optimised Retrieval Model (ORM),
originally developed as the scientific prototype of the ESA level-2 processor for MIPAS observations. The results of the analyses have been included into the
MIPAS level-2 version 8 (level2-v8) database containing atmospheric fields of pressure, temperature, and volume mixing ratio (VMR) of
MIPAS main targets H2O, O3, HNO3, CH4, N2O, and
NO2, along with the minor gases CFC-11, ClONO2, N2O5,
CFC-12, COF2, CCl4,
CF4, HCFC-22, C2H2, CH3Cl, COCl2,
C2H6, OCS, and HDO.
The database covers all the measurements acquired by MIPAS in the nominal measurement mode of the full
resolution (FR) part of the mission (from July 2002 to March 2004) and all the observation modes of the optimised resolution (OR) part (from January 2005 to
April 2012). The number of species included in the MIPAS level2-v8 dataset
makes it of particular importance for the studies of stratospheric chemistry. The database is considered by ESA the
final release of the MIPAS level-2 products. The ORM algorithm is operated at the vertical grid coincident to the tangent altitudes of the observations or to a subset of them, spanning (in the nominal mode) the altitude range from 6 to 68 km in the FR phase and from 6 to 70 km in the OR period. In the latitude domain, FR profiles are spaced by about 4.7∘, while the OR profiles are spaced by about 3.7∘. For each retrieved species, the auxiliary data and the retrieval choices are described. Each product is characterised in terms of the retrieval error, spatial resolution, and “useful” vertical range in both phases of the MIPAS mission. These depend on the characteristics of the measurements (spectral and vertical resolution of the measurements), the retrieval choices (number of spectral points included in the analyses, number of altitudes included in the vertical retrieval grid), and the information content of the measurements for each trace species. For temperature, water vapour, ozone, and nitric acid, the number of degrees of freedom is significantly larger in the OR phase than in the FR one, mainly due to the finer vertical measurement grid. In the FR phase, some trace species are characterised by a smaller retrieval error with respect to the OR phase, mainly due to the larger number of spectral points used in the analyses, along with the reduced vertical resolution.
The way of handling possible caveats (negative VMR, vertical grid representation) is discussed. The quality of the retrieved profiles is assessed through four criteria, two providing information on the successful convergence of the retrieval iterations, one on the capability of the retrieval to reproduce the measurements, and one on the presence of outliers. An easy way to identify and filter the problematic profiles with the information contained in the output files is provided.
MIPAS level2-v8 data are available to the scientific community through the ESA portal (https://doi.org/10.5270/EN1-c8hgqx4).