Starting from 2019, the Italian Space Agency (ASI) is supporting dedicated projects for the development of new methods, tools and competences for the interpretation and the exploitation of the future measurements of the FORUM (Far-infrared Outgoing Radiation Understanding and Monitoring) experiment. FORUM will be the ninth Earth Explorer mission of the European Space Agency, scheduled for launch on a polar orbiting satellite in 2027. The core instrument of the mission will be a Fourier Transform Spectrometer with spectral range extending down to the Far-InfraRed (FIR), from 100 to 1600 cm-1 (from 100 to 6.25 microns in wavelength), thus covering the whole Earth's outgoing longwave radiation spectrum. FORUM will fly in loose formation with the MetOp-SG-A satellite, hosting the Infrared Atmospheric Sounding Interferometer - New Generation (IASI-NG). The Middle-InfraRed (MIR) range (645 to 2760 cm-1) of the upwelling atmospheric spectrum measured by IASI-NG will effectively complement the FORUM measurement. All together, the two missions will provide matching spectral radiance measurements with unprecedented coverage, from 100 to 2760 cm-1. While the FIR part of the spectrum (100-667 cm-1) measured by FORUM is the most sensitive to the water vapour content in the UTLS and to ice cloud properties, the atmospheric windows in the MIR are measured by IASI-NG with a very high signal-to-noise ratio, thus supplying very precise information on the surface temperature and on the temperature profile, which are essential to constrain the retrieval of the other geophysical parameters. To get ready for the exploitation of the synergistic FORUM and IASI-NG measurements, in the frame of the mentioned ASI projects a Bayesian retrieval algorithm with the capability to perform the simultaneous inversion of two different synergistic spectral radiance measurements was developed. The tool is named FAst Retrieval Model (FARM) as it is based on a fast monochromatic and parametrized radiative transfer model (?-IASI) which is also being further extended and refined within the same projects. FARM includes the capability to retrieve simultaneously both atmospheric and cloud parameters. Furthermore, the code can handle both air/space- borne nadir measurements and ground- based zenith measurements. In this work, we introduce the functionalities of the developed algorithm and present the results of the self-consistency and verification tests. The preliminary results of the inversion of some existing real measurements are also discussed.

MIPAS is a Fourier Transform spectrometer that measured the atmospheric limb emission spectra in the middle infrared on board the ENVISAT satellite. These measurements allowed the global monitoring of the three-dimensional (latitude, longitude and altitude) distribution of temperature and of the concentrations of many species, during both day and night, for 10 years, from July 2002 to April 2012. MIPAS measurements allowed to study the atmosphere from the upper troposphere to the stratosphere and above, up to the thermosphere. The interest in these measurements goes beyond the end of the mission, as they can be used in long time series of data to determine changes in atmospheric composition and in our planet's climate. Furthermore, if the Changing-Atmosphere Infra-Red Tomography Explorer (CAIRT) mission, one of four candidates for Earth Explorer 11, will be selected, MIPAS data will constitute a benchmark for these measurements. CAIRT exploits indeed the heritage of MIPAS on ENVISAT, but allows to measure the composition of the atmosphere with unprecedented three-dimensional resolution being the first imaging Fourier Transform spectrometer sounding the limb of the atmosphere from space. For the last reanalysis of the whole MIPAS mission, a significant effort was made by the MIPAS Quality Working Group, supported by ESA, to improve both L1 [1] and L2 processors, as well as spectroscopy and Level 2 Initial Guess profiles [2], with the objectives of obtaining L2 products with increased accuracy, better temporal stability, and a larger number of retrieved species. The main improvements of L1 processor were related to the radiometric calibration and pointing. With these new processors a MIPAS full mission reprocessing has been recently performed ([1] and [3]). The quality of this final operational data set has been assessed with comprehensive validation studies including comparisons to ground-based in-situ and balloon-borne measurements. The dataset containing the new version 8 of both L1 and L2 products and covering the entire MIPAS operational lifetime period (2002-2012) is available at ESA Earth Online web site.This paper will focus on the lessons learnt, on the quality of the reprocessed data, on the remaining problems, and on further improvements that could improve the quality of both MIPAS L1 and L2 datasets.[1] Kleinert et al. Kleinert, A., Birk, M., Perron, G., and Wagner, G.: Level 1b error budget for MIPAS on ENVISAT, Atmos. Meas. Tech., 11, 5657-5672,https://doi.org/10.5194/amt-11-5657-2018, 2018 [2] Raspollini, P., Arnone, E., Barbara, F., Bianchini, M., Carli, B., Ceccherini, S., Chipperfield, M. P., Dehn, A., Della Fera, S., Dinelli, B. M., Dudhia, A., Flaud, J.-M., Gai, M., Kiefer, M., López-Puertas, M., Moore, D. P., Piro, A., Remedios, J. J., Ridolfi, M., Sembhi, H., Sgheri, L., and Zoppetti, N.: Level 2 processor and auxiliary data for ESA Version 8 final full mission analysis of MIPAS measurements on ENVISAT, Atmos. Meas. Tech. Discuss. [preprint], https://doi.org/10.5194/amt-2021-235, in review, 2021. [3] Dinelli, B. M., Raspollini, P., Gai, M., Sgheri, L., Ridolfi, M., Ceccherini, S., Barbara, F., Zoppetti, N., Castelli, E., Papandrea, E., Pettinari, P., Dehn, A., Dudhia, A., Kiefer, M., Piro, A., Flaud, J.-M., Lopez-Puertas, M., Moore, D., Remedios, J., and Bianchini, M.: The ESA MIPAS/ENVISAT Level2-v8 dataset: 10 years of measurements retrieved with ORM v8.22, Atmos. Meas. Tech. Discuss. [preprint], https://doi.org/10.5194/amt-2021-215, accepted, 2021.

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.

Questo documento riassume l'attività svolta nei vari WP, le azioni completate e lo stato di del progetto progetto per il periodo di attività dal 9 giugno 2021 (RA3) al 19 aprile 2022 (RA4)

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) measured the middle-infrared limb emission spectrum of the atmosphere from 2002 to 2012 on board ENVISAT, a polar-orbiting satellite. Recently, the European Space Agency (ESA) completed the final reprocessing of MIPAS measurements, using version 8 of the level 1 and level 2 processors, which include more accurate models, processing strategies, and auxiliary data. The list of retrieved gases has been extended, and it now includes a number of new species with weak emission features in the MIPAS spectral range. The new retrieved trace species include carbonyl chloride (COCl2), also called phosgene. Due to its toxicity, its use has been reduced over the years; however, it is still used by chemical industries for several applications. Besides its direct injection in the troposphere, stratospheric phosgene is mainly produced from the photolysis of CCl4, a molecule present in the atmosphere because of human activity. Since phosgene has a long stratospheric lifetime, it must be carefully monitored as it is involved in the ozone destruction cycles, especially over the winter polar regions.In this paper we exploit the ESA MIPAS version 8 data in order to discuss the phosgene distribution, variability, and trends in the middle and lower stratosphere and in the upper troposphere. The zonal averages show that phosgene volume mixing ratio is larger in the stratosphere, with a peak of 40 pptv (parts per trillion by volume) between 50 and 30 hPa at equatorial latitudes, while at middle and polar latitudes it varies from 10 to 25 pptv. A moderate seasonal variability is observed in polar regions, mostly between 80 and 50 hPa. The comparison of MIPAS-ENVISAT COCl2 v8 profiles with the ones retrieved from MIPAS balloon and ACE-FTS (Atmospheric Chemistry Experiment - Fourier Transform Spectrometer) measurements highlights a negative bias of about 2 pptv, mainly in polar and mid-latitude regions. Part of this bias is attributed to the fact that the ESA level 2 v8 processor uses an updated spectroscopic database. For the trend computation, a fixed pressure grid is used to interpolate the phosgene profiles, and, for each pressure level, VMR (volume mixing ratio) monthly averages are computed in pre-defined 10? wide latitude bins. Then, for each latitudinal bin and pressure level, a regression model has been fitted to the resulting time series in order to derive the atmospheric trends. We find that the phosgene trends are different in the two hemispheres. The analysis shows that the stratosphere of the Northern Hemisphere is characterized by a negative trend of about -7 pptv per decade, while in the Southern Hemisphere phosgene mixing ratios increase with a rate of the order of +4 pptv per decade. This behavior resembles the stratospheric trend of CCl4, which is the main stratospheric source of COCl2. In the upper troposphere a positive trend is found in both hemispheres.

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 MI- PAS level-2 version 8 (level2-v8) database containing atmospheric fields of pressure, temperature, and volume mixing ratio (VMR) of MIPAS main targets H2 O, O3 , HNO3 , CH4 , N2 O, and NO2 , along with the minor gases CFC- 11, ClONO2 , N2 O5 , CFC-12, COF2 , CCl4 , CF4 , HCFC-22, C2 H2 , CH3 Cl, COCl2 , C2 H6 , 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 alti- tude range from 6 to 68km in the FR phase and from 6 to 70 km in the OR period. In the latitude domain, FR profiles are spaced by about 4.7o, while the OR profiles are spaced by about 3.7o. 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 in- cluded 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 informa- tion 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).

Questo documento riassume l'attività svolta nei vari WP, le azioni completate e lo stato di del progetto per il periodo di attività dal 16 giugno 2020 (RA2) al 9 giugno 2021 (RA3).

Questo documento riassume l'attività svolta nei vari WP, le azioni completate e lo stato di del progetto per il periodo di attività dal 19 febbraio 2020 (RA1) al 16 giugno 2020 (RA2).

MIPAS is a Fourier Transform spectrometer that measured the atmospheric limb emission spectra in the middle infrared on board the ENVISAT satellite. These measurements allowed the global monitoring of the three-dimensional (latitude, longitude and altitude) distribution of concentrations of many species, during both day and night, for 10 years, from July 2002 to April 2012. Being a limb sounding instrument, the focus of MIPAS measurements was the study of the atmosphere from the upper troposphere to the stratosphere and above, up to the mesosphere. The interest in these measurements goes beyond the end of the mission, as they can be used in long time series of data to determine changes in our planet's climate. To this purpose, it is therefore important to continue improving their quality. The quality of MIPAS L2 products depends on the quality of the L1 products, on the L2 model accuracy, on the quality of auxiliary data, particularly on spectroscopic data. For the last reanalysis of the whole MIPAS mission, a significant effort was made by the MIPAS Quality Working Group, supported by ESA, to improve both L1 and L2 processors, as well as spectroscopy, with the objectives of obtaining L2 products with increased accuracy, better temporal stability, and a larger number of retrieved species. Here we present the full mission dataset, including vertical profiles of 21 trace species plus temperature, obtained by applying the latest version of ESA L2 processor (ORM V8) to the MIPAS L1 data obtained with version 8 of the L1 processor. The impact of the improvements of both L1 and L2 processors on the quality of the L2 products is presented, as well as results of the validation against independent correlative measurements.

Riporta i principali risultati ottenuti nell'ambito del progetto: "Support to MIPAS Level 2 processor Verification and Validation - Phase F", Contratto ESA 4000112093/14/I-LG, cioe' la messa a punto del codice ORM_V8 da utilizzare per la rianalisi di livello 2 dell'intera missione di MIPAS/ENVISAT, il dataset processato, i test di verifica e di validazione dei prodotti di Livello 2 generati.

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is a limb-viewing infrared Fourier transform spectrometer that operated from 2002 to 2012 onboard the ENVISAT satellite. The analysis of MIPAS measurements allows to study the temporal evolution of numerous species of interest for the study of the ozone in the stratosphere, pollutants and many green-house gases. The objective of the MIPAS Quality Working Group is to improve the quality of the MIPAS products through a fruitful collaboration among spectroscopists, Level 1, Level 2, and validation teams. A large effort has recently led to implement significant improvements in both ESA Level 1 and Level 2 processors, as well as in spectroscopic database and in some absorption cross-sections in order to improve the quality of the products. In addition to the products already present in the V7 dataset (temperature and the VMR of H2O, O3, HNO3, CH4, N2O, NO2, CFC-11, CFC-12, N2O5, ClONO2, HCFC-22, COF2, CF4, HCN and CCl4), the VMR of six additional species (OCS, CH3Cl, HDO, C2H2, C2H6, COCl2) will be provided in V8 dataset. In order to evaluate the impact of the changes in the products before full mission reprocessing, the analysis of the performances of the products of the modified L1 and L2 processors, as well as the auxiliary data, has been performed on a Diagnostic DataSet (DDS). The orbits of the DDS have been chosen in coincidence with correlative measurements for performing also a preliminary assessment of the accuracy of the products and to evaluate possible changes in the drift. With respect to V7 products, main improvements consist in a reduction of the temperature bias in the first part of the mission, a reduction of the discontinuities in CH4 and N2O time series due to daily gain upgrade, a better filtering of clouds and a better handling of horizontal inhomogeneities.The results of the assessment of the quality of MIPAS measurements will be shown, as well as the study of the temporal evolution and variability of all species. We will also investigate the spatial, seasonal, and interannual variations in the distribution of these species.

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is a limb-viewing infrared Fourier transform spectrometer that operated from 2002 to 2012 on board the ENVISAT satellite. The fruitful collaboration among spectroscopists, Level 1, Level 2, and validation teams in the frame of the MIPAS Quality Working Group has recently led to the implementation of significant changes in both ESA Level 1 and Level 2 processors, as well as in the spectroscopic database and in some absorption cross-sections. In addition to the products already present in V7 dataset (temperature and the VMR of H2O, O3, HNO3, CH4, N2O, NO2, CFC-11, CFC-12, N2O5, ClONO2, HCFC-22, COF2, CF4, HCN and CCl4), the VMR of six additional species (OCS, CH3Cl, HDO, C2H2, C2H6, COCl2) will be provided in V8 dataset.Among the new species, methyl chloride (CH3Cl) is of great interest in stratospheric ozone chemistry since it is the most abundant chlorine-containing gas in the troposphere and, in contrast to other relatively long-lived ozone-depleting gases, it has both natural and anthropogenic sources, with the known emission being mainly natural (tropical plants, biomass burning, the ocean, salt marshes and fungi). Since it is not controlled under the Montreal Protocol, its importance is expected to increase in the coming decades as emission controls alter the relative contributions from natural and anthropogenic halogen sources.In this paper we present a preliminary assessment of the quality of the MIPAS CH3Cl data, in terms of precision, accuracy and vertical resolution, and we investigate the spatial and seasonal variations in the distribution of CH3Cl in the upper troposphere/lower stratosphere (UTLS).

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) is a limb-viewing infrared Fourier transform spectrometer that operated from 2002 to 2012 onboard the ENVISAT satellite. The maintenance and the upgrade of both L1 and L2 ESA processors are accomplished by the Quality Working Group, where a fruitful collaboration among Level 1, Level 2 and validation teams can be exploited. Recently both ESA L1 and L2 processors have been updated, as well as the spectroscopic database and some absorption cross-sections. In addition to the products already present in the current release (V7) of ESA MIPAS data (temperature and the VMR of H2O, O3, HNO3, CH4, N2O, NO2, CFC-11, CFC-12, N2O5, ClONO2, HCFC-22, COF2, CF4, HCN and CCl4), the VMR of six additional species (OCS, CH3Cl, HDO, C2H2, C2H6, COCl2) will be provided in V8 dataset. In preparation of V8 full mission reprocessing, three Diagnostic Datasets have been generated to check the performances of all L1, L2 processors and the new auxiliary data.The analysis of these Diagnostic Datasets and the comparison with previous full mission dataset V7 will be used to perform a first assessment of the quality of the new V8 products. In the paper special focus will be given to the new species.

The Optimized Retrieval Code (ORM) was originally designed to be the scientific code used as the reference for the ESA operational Near Real Time Analysis of MIPAS measurements on ENVISAT. After the end of ENVISAT mission, occurred on April 2017, this code has been adapted and improved to perform the reanalysis of the full MIPAS mission.

MIPAS on ENVISAT performed almost continuous and global measurements of atmospheric temperature and composition from June 2002 to April 2012. These data are very useful for understanding atmosphere climatology from the upper troposphere to the mesosphere, including trends in composition and variability, as a reference for middle atmosphere ozone and general circulation as well as improvement of tropospheric composition retrievals. The ESA Level 2 processor, based on the Optimized Retrieval Model (ORM), originally designed for the Near Real Time analysis and developed by an European Consortium led by IFAC, is currently improved and used for the reanalysis of the full MIPAS mission. The maintenance and the upgrade of the ESA processor are made in the frame of the MIPAS Quality Working Group, where a fruitful collaboration among Level 1, Level 2 and validation teams is exploited. This collaboration is essential to improve the accuracy of the products and their characterization. This paper is meant to describe the most recent upgrades in the MIPAS processor, in particular the full mission was recently reprocessed with L1 V7 and L2 V7 processors, containing significant improvements with respect to previous version 6, and further improvements are in preparation, that will be collected in version 8 of the ESA processor. The improvements include both L1 and L2 processors, as well as the auxiliary data. In the L1 processor the correction of the instrumental drift caused by the ageing of the detectors has been implemented in order to reduce the non negligible systematic error in the trend estimation. Furthermore, the measured daily gain instead of the weekly gain is now used for the radiometric calibration that allows to better take account for the discontinuities in the gain that occasionally occur in MIPAS band B. Improvements in the L2 processor include a different approach for retrieving atmospheric continuum, the use of an a posteriori regularization with altitude dependent constraint, a better approach for handling interfering species, a reduced bias in CFC-11, the handling of horizontal inhomogeneities and the use of ECMWF altitude/pressure relation to determine more accurate altitudes. Improvements in the auxiliary data consist in the use of microwindows with larger information content, an improved spectroscopic database and diurnally varying climatological dataset. Furthermore, additional species are provided in the new processors, leading to a total of 22 retrieved species by the L2 version 8 processor. Each of these changes has a different impact on the Level 2 products. The individual contributions, as well as the cumulative effects, will be evaluated with a comparison with previous versions of MIPAS products and corresponding results of validation. Improvements in the trend determination will also be evaluated, as well as the quality of the new retrieved species.

MIPAS on ENVISAT performed almost continuous measurements of atmospheric composition for approximately 10 years, from June 2002 to April 2012. ESA processor, based on the algorithm ORM (Optimized Retrieval Model), originally designed for the Near Real Time analysis and developed by an European Consortium led by IFAC, is currently used for the reanalysis of the full MIPAS mission. The maintenance and the upgrade of the ESA processor are made in the frame of the Quality Working Group, where a fruitful collaboration among Level 1, Level 2 and validation teams can be exploited. This collaboration is essential to pursue improvements in the accuracy of the products and their characterization. This paper is meant to describe the most recent upgrades in the ESA processor performed to improve the quality of ESA products. In particular, the full mission was recently reprocessed with L1 V7 and L2 V7 processors, containing significant improvements with respect to previous version V6, and further improvements are in preparation, that will be collected in version 8 of the ESA processor. Improvements involve both L1 and L2 processors, as well as the auxiliary data. Improvements in the L1 processor consist in a correction of the instrumental drift, improved spike detection algorithm and new Instrument Line Shape, as well as the use of measured daily gain instead of weekly gain. Improvements in the L2 processor include a different approach for retrieving atmospheric continuum, the use of an a posteriori regularization with altitude dependent constraint, a better approach for handling interfering species, a reduced bias in CFC-11, the handling of horizontal inhomogeneities and the use of ECMWF altitude/pressure relation for determining more accurate altitudes. Improvements in the auxiliary data consist in the use of microwindows with larger information content, new spectroscopic database and diurnally varying climatological dataset. Furthermore, with each new version additional species are provided, leading to 20 the number of retrieved species by the L2 V8 processor. Improvements in the V7 products will be revised on the light of the results of the validation with correlative measurements, and, by comparing the first new L2 V8 products with the L2 V7 ones, a preliminary assessment of the performance of the new V8 processor will be performed.

We present the results of the algorithm modeling the horizontal gradients in the ESA retrieval of MIPAS data ORM v8.

MIPAS on ENVISAT performed almost continuously measurements of the atmospheric composition for almost 10 years, from June 2002 to April 2012. These ten years cover a period when the first effect of the dismiss of the emission of the CFCs after the Montreal protocol ratification in 1987can be measured. Even if ten years constitute a short period to derive trends, it has been proven that useful information on time variation of atmospheric constituents can be derived from the analysis of these measurements. However, previous versions of MIPAS on ENVISAT dataset were characterized by an instrumental drift due to the fact that some detectors used by MIPAS were affected by non-linearities, which change with time due to the ageing of the detectors and this was cause of a non negligible systematic error in the trend estimation. The new full mission reprocessed dataset V7 that will be released very soon uses L1 files where the impact of the ageing of the detectors on non-linearities has been corrected. Furthermore, also the L2 processor has been upgraded with new functionalities improving the performances of the processor. We present the results of study of trends derived from the analysis of the new MIPAS V7 products on several MIPAS target species including ozone depleting species, like CFC-11, CFC-12, CCl4 and HCFC-22.

MIPAS measurements on ENVISAT represent a unique database for the study of atmospheric composition and of the time variation of atmospheric constituents. For trend studies it is important that instrumental drifts are reduced. Some of the MIPAS spectral bands are affected by time-dependent non-linearity which have been recently corrected. In addition to this non-linearity correction, the forthcoming new version of MIPAS products (Version 7) contains several other improvements: a new approach for handling continuum capable of making the retrieval more stable, a new selection of spectral intervals selected for the analysis of the full resolution measurements aimed to reduce the bias between full resolution and optimized resolution measurements, the regularization of the H2O profiles, the products of five new species (HCFC-22, CFC-14, HCN, COF2, CCl4), which makes equal to 15 the total number of retrieved species. The latest improvements implemented in the ESA processor and some of the results on trend will be presented and discussed.

The ESA-ESRIN contract no. 21719/08/I-OL covered the activities performed between April 2008 and July 2014 by the L2 sub-group of the MIPAS Quality Working Group. The main objective of this project was to monitor the quality of MIPAS L2 products, to improve the performances of the L2 ESA processor, used for both the near real time analysis during ENVISAT mission and for the off-line analysis, and to enlarge the list of retrieved species. In particular, three different versions of the MIPAS operational processor were finalized: IPF V5, ML2PP V6 and ML2PP V7, leading to significant improvements in the quality of the products and in their diagnostics, to an increase of the number of processed scans, and to an enlargement of the list of provided products. With respect to IPF V4.1&2, used to process only the first two years of MIPAS measurements (2002-2004, Full Resolution (FR) measurements) and validated with respect to correlative measurements (Ridolfi et al., 2006, Cortesi et al., 2007, Wang et al., 2007, Payan et al., 2009, Wetzel et al., 2007, Wetzel et al., 2013, all contained in the MIPAS special issue), IPF V5: o performs the analysis of the full mission (both FR and Optimized Resolution (OR) measurements, characterized by a reduced spectral resolution but finer spatial resolution) after the introduction of an a posteriori regularization with self-adapting threshold aimed to reduce instabilities of the retrieval with measurements of the OR phase (due to sampling intervals finer than the instantaneous field of view of the instrument and the choice of using a retrieval grid aligned with the vertical sampling of the measurements); o provides as output Averaging Kernel (AK) for each scan. Products of ML2PP V6 are very similar to the ones of V5 in terms of bias, but are characterized by: o an improved diagnostics, since the Covariance Matrix and the AK matrix are computed taking into account all iterations performed during the retrieval (this is needed if the final Marquardt parameter is different from zero). Furthermore, horizontal AKs are provided for each latitude band and each season. o additional four new species, namely CFC-11, CFC-12, N2O5 and ClONO2. MIPAS ESA processor products V7 are characterized by: o reduced time dependent calibration error due to non-linearities (coming from using new L1 data, V7); o availability of retrieval altitude grid characterized by a very small bias after correction with ECMWF pressure/altitude relationship; o new microwindows for FR measurements with an increased information content and leading to a reduction of the detected bias in the FR measurements for CH4, N2O and CFC-12; o larger stability, given by the new approach for retrieving continuum (the continuum transmission is fitted instead of the continuum cross-section), and new regularization with altitude dependent regularization strength; o lower bias of CFC-11, due to proper handling of COCl2 interfering species in the retrieval o better representation of the measurements, proven by the fact that a smaller chi-square is obtained for most of the species; o better handling of diurnally varying interfering species, coming from the use of diurnally varying Initial Guess profiles; o products of five new species (HCFC-22, CFC-14, COF2, CCl4 and HCN) available. Concerning V7 products, preliminary verifications have been performed only on the diagnostic dataset V7, including more than 4000 orbits: the Non-Linearity correction performed in the L1 files introduces a drift in V7 profiles with respect to previous versions, that corrects for the instrumental drift present in previous datasets. Some problems have also been identified: V7 FR Temperature profiles in polar and midlatitude regions presents a negative bias of about 0.5-1K with respect to both V6 products and correlative measurements coming from the Non-Linearity correction. In the tropics in general V7 Temperature has a positive bias with respect to previous versions, for both FR and OR measurements, and this seems to come from the new approach for handling continuum. A new version of the spectroscopic database has been finalized, with improvements in H2O, HNO3, COCl2 and C3H8. The new version of the spectroscopic database will be used for the final reprocessing of the whole MIPAS mission in the frame of the subsequent contract. A large effort was spent for improving the quality of the MIPAS L2 products, but further improvements have been identified as needed to reduce some systematic errors of the products and to fully exploit the information contained in MIPAS measurements. One of the main problems identified so far is the error due to the horizontal inhomogeneities that are not currently taken into account by the algorithm. The quality of the retrieval is affected by the horizontal gradients but from the analysis of single scans no enough information is contained in the measurements to retrieve the gradients. Considering that the code will be used only for a reanalysis, the choice has been to take advantage of the information on horizontal gradients of both temperature and target species from previous reprocessing or ECMWF reanalysis and to modify the forward model in order to handle the externally provided gradients. Another important objective is the full exploitation of MIPAS measurements that implies the retrieval of weaker and weaker species, whose interference from other species cannot be disentangled. To this purpose the possibility of performing a multi-target retrieval is crucial. Furthermore, we have to consider that the vertical profile retrieval of weak species requires the use of some constraint for the attainment of a fast and useful product and it can be useful to have the possibility of tuning or removing it as needed during the average procedure. To this purpose Optimal Estimation seems to be more apt than the current approach where the constraint is determined with a self-consistent method, difficult to rebuild. For very weak species a posteriori averages of retrieved profiles after removing a priori constrain, as studied in the frame of this project, can be also considered. Validation of ML2PP V7 and further investigations aimed to solve these open issues will be completed in the frame of the subsequent contract.