We report on the retrieval of PAN (CH3C(O)OONO2) in the upper tropical troposphere from limb measurements by the remote-sensor MIPAS-STR on board the Russian high altitude research aircraft M55-Geophysica. The measurements were performed close to Araçatuba, Brazil, on 17 February 2005. The retrieval was made in the spectral range 775–820 cm−1 where PAN exhibits its strongest feature but also more than 10 species interfere. Especially trace gases such as CH3CCl3, CFC-113, CFC-11, and CFC-22, emitting also in spectrally broad not-resolved branches, make the processing of PAN prone to errors. Therefore, the selection of appropriate spectral windows, the separate retrieval of several interfering species and the careful handling of the water vapour profile are part of the study presented. The retrieved profile of PAN has a maximum of about 0.14 ppbv at 10 km altitude, slightly larger than the lowest reported values (<0.1 ppbv) and much lower than the highest reported in the literature (0.65 ppbv). Besides the NOy constituents measured by MIPAS-STR (HNO3, ClONO2, HO2NO2, PAN), the in situ instruments aboard the Geophysica provide simultaneous measurements of NO, NO2, and the sum NOy. Comparing the sum of in-situ and remotely derived NO+NO2+HNO3+ClONO2+HO2NO2+PAN with total NOy a deficit of 30–40% (0.2–0.3 ppbv) in the troposphere remains unexplained whereas the values fit well in the stratosphere.

Altitude profiles of ClONO2 retrieved with the IMK (Institut fur Meteorologie und Klimaforschung) science-oriented data processor from MIPAS/Envisat (Michelson Interferometer for Passive Atmospheric Sounding on Envisat) mid-infrared limb emission measurements between July 2002 and March 2004 have been validated by comparison with balloon-borne (Mark IV, FIRS2, MIPAS-B), airborne (MIPAS-STR), ground-based (Spitsbergen, Thule, Kiruna, Harestua, Jungfraujoch, Izana, Wollongong, Lauder), and spaceborne (ACE-FTS) observations. With few exceptions we found very good agreement between these instruments and MIPAS with no evidence for any bias in most cases and altitude regions. For balloon-borne measurements typical absolute mean differences are below 0.05 ppbv over the whole altitude range from 10 to 39 km. In case of ACE-FTS observations mean differences are below 0.03 ppbv for observations below 26 km. Above this altitude the comparison with ACE-FTS is affected by the photochemically induced diurnal variation of ClONO2. Correction for this by use of a chemical transport model led to an overcompensation of the photochemical effect by up to 0.1 ppbv at altitudes of 30-35 km in case of MIPAS-ACE-FTS comparisons while for the balloon-borne observations no such inconsistency has been detected. The comparison of MIPAS derived total column amounts with ground-based observations revealed no significant bias in the MIPAS data. Mean differences between MIPAS and FTIR column abundances are 0.11 +/- 0.12 x 10(14) cm(-2) (1.0 +/- 1.1%) and -0.09 +/- 0.19 x 10(14) cm(-2) (-0.8 +/- 1.7%), depending on the coincidence criterion applied. chi(2) tests have been performed to assess the combined precision estimates of MIPAS and the related instruments. When no exact coincidences were available as in case of MIPAS-FTIR or MIPAS-ACE-FTS comparisons it has been necessary to take into consideration a coincidence error term to account for chi(2) deviations. From the resulting chi(2) profiles there is no evidence for a systematic over/underestimation of the MIPAS random error analysis.

Nitric acid (HNO3) is one of the key products that are operationally retrieved by the European Space Agency (ESA) from the emission spectra measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) onboard ENVISAT. The product version 4.61/4.62 for the observation period between July 2002 and March 2004 is validated by comparisons with a number of independent observations from ground-based stations, aircraft/balloon campaigns, and satellites. Individual HNO3 profiles of the ESA MIPAS level-2 product show good agreement with those of MIPAS-B and MIPAS-STR (the balloon and aircraft version of MIPAS, respectively), and the balloon-borne infrared spectrometers MkIV and SPIRALE, mostly matching the reference data within the combined instrument error bars. In most cases differences between the correlative measurement pairs are less than 1 ppbv (5–10%) throughout the entire altitude range up to about 38 km (~6 hPa), and below 0.5 ppbv (15–20% or more) above 30 km (~17 hPa). However, differences up to 4 ppbv compared to MkIV have been found at high latitudes in December 2002 in the presence of polar stratospheric clouds. The degree of consistency is further largely affected by the temporal and spatial coincidence, and differences of 2 ppbv may be observed between 22 and 26 km (~50 and 30 hPa) at high latitudes near the vortex boundary, due to large horizontal inhomogeneity of HNO3. Similar features are also observed in the mean differences of the MIPAS ESA HNO3 VMRs with respect to the ground-based FTIR measurements at five stations, aircraft-based SAFIRE-A and ASUR, and the balloon campaign IBEX. The mean relative differences between the MIPAS and FTIR HNO3 partial columns are within ±2%, comparable to the MIPAS systematic error of ~2%. For the vertical profiles, the biases between the MIPAS and FTIR data are generally below 10% in the altitudes of 10 to 30 km. The MIPAS and SAFIRE HNO3 data generally match within their total error bars for the mid and high latitude flights, despite the larger atmospheric inhomogeneities that characterize the measurement scenario at higher latitudes. The MIPAS and ASUR comparison reveals generally good agreements better than 10–13% at 20–34 km. The MIPAS and IBEX measurements agree reasonably well (mean relative differences within ±15%) between 17 and 32 km. Statistical comparisons of the MIPAS profiles correlated with those of Odin/SMR, ILAS-II, and ACE-FTS generally show good consistency. The mean differences averaged over individual latitude bands or all bands are within the combined instrument errors, and generally within 1, 0.5, and 0.3 ppbv between 10 and 40 km (~260 and 4.5 hPa) for Odin/SMR, ILAS-II, and ACE-FTS, respectively. The standard deviations of the differences are between 1 to 2 ppbv. The standard deviations for the satellite comparisons and for almost all other comparisons are generally larger than the estimated measurement uncertainty. This is associated with the temporal and spatial coincidence error and the horizontal smoothing error which are not taken into account in our error budget. Both errors become large when the spatial variability of the target molecule is high.

Altitude profiles of ClONO2 retrieved with the IMK (Institut für Meteorologie und Klimaforschung) science-oriented data processor from MIPAS/Envisat (Michelson Interferometer for Passive Atmospheric Sounding on Envisat) mid-infrared limb emission measurements between July 2002 and March 2004 have been validated by comparison with balloon-borne (Mark IV, FIRS2, MIPAS-B), airborne (MIPAS-STR), ground-based (Spitsbergen, Thule, Kiruna, Harestua, Jungfraujoch, Izaña, Wollongong, Lauder), and spaceborne (ACE-FTS) observations. With few exceptions we found very good agreement between these instruments and MIPAS with no evidence for any bias in most cases and altitude regions. For balloon-borne measurements typical absolute mean differences are below 0.05 ppbv over the whole altitude range from 10 to 39 km. In case of ACE-FTS observations mean differences are below 0.03 ppbv for observations below 26 km. Above this altitude the comparison with ACE-FTS is affected by the photochemically induced diurnal variation of ClONO2. Correction for this by use of a chemical transport model led to an overcompensation of the photochemical effect by up to 0.1 ppbv at altitudes of 30–35 km in case of MIPAS-ACE-FTS comparisons while for the balloon-borne observations no such inconsistency has been detected. The comparison of MIPAS derived total column amounts with ground-based observations revealed no significant bias in the MIPAS data. Mean differences between MIPAS and FTIR column abundances are 0.11±0.12×1014 cm−2 (1.0±1.1%) and −0.09±0.19×1014 cm−2 (−0.8±1.7%), depending on the coincidence criterion applied. χ2 tests have been performed to assess the combined precision estimates of MIPAS and the related instruments. When no exact coincidences were available as in case of MIPAS – FTIR or MIPAS – ACE-FTS comparisons it has been necessary to take into consideration a coincidence error term to account for χ2 deviations. From the resulting χ2 profiles there is no evidence for a systematic over/underestimation of the MIPAS random error analysis.

umn abundances are 0.11 0.12 cm (1.0 1.1%) and -0.09 0.19 cm (-0.8 1.7%), depending on the coincidence criterion applied. tests have been performed to assess the combined precision estimates of MIPAS and the related instruments. When no exact coincidences were available as in case of MIPAS FTIR or MIPAS - ACE-FTS comparisons it has been necessary to take into consideration a coincidence error term to account for deviations. From the resulting profiles there is no evidence for a systematic over/underestimation of the MIPAS random error analysis.

the planning of all subsequent balloon and aircraft missions of the ESABC programme. We report on the validation of profiles of the MIPAS processor of ESA version 4.61 with correlative data derived from balloon and aircraft measurements. The activities were part of the ENVISAT Stratospheric Aircraft and Balloon Campaign (ESABC) [1]. The paper includes contributions from five experiments flown on stratospheric balloons and one from the highaltitude aircraft Geophysica. 1 2

RESUME The ENVISAT validation programme for the atmospheric instruments MIPAS, SCIAMACHY and GOMOS is based on a number of balloon-bone, aircraft and ground-based correlative measurements. In particular the activities of validation scientists were coordinated by ESA within the ENVISAT Stratospheric Aircraft and Balloon Campaign or ESABC. As a companion to a similar paper on CH4 and in parallel to the contribution of the individual validation teams, the present paper provides a synthesis of comparisons performed between MIPAS N2O profiles produced by the current ESA operational software (Instrument Processing Facility version 4.61 or IPF v4.61) or by the IMK-FZK scientific processor and correlative measurements obtained from balloon and aircraft experiments as well as from ground-based instruments.

RESUME The ENVISAT validation programme for the atmospheric instruments MIPAS, SCIAMACHY and GOMOS included a number of balloon-borne, aircraft, other satellite and ground-based correlative measurements. In particular the activities of validation scientists were coordinated by ESA within the ENVISAT Stratospheric Aircraft and Balloon Campaign or ESABC. In parallel to the contribution of the individual validation teams, the present paper provides a synthesis of comparisons made between MIPAS CH4 profiles produced by the current ESA operational software (Instrument Processing Facility version 4.61 i.e. IPF v4.61) or by the IMK-FZK scientific processor and correlative measurements obtained from balloon and aircraft experiments as well as from satellite sensors or from ground-based instruments.

A number of in situ and remote sensing techniques for the measurement of upper tropospheric and stratospheric O3 content was employed during dedicated experiments of the ESABC programme, aiming at the validation of the ENVISAT chemistry payload. In this paper, we will be focusing on the validation of MIPAS off-line products, by presenting the results of the intercomparison between MIP AS O3 vertical profiles and aircraft and balloon correlative measurements. First priority is given to the validation of processor v4.61 data, but individual results of 2002 and 2003 balloon observations are also compared with MIPAS O3 non operational data. Some general remarks are finally expressed, along with specific recommendation to fully exploit the available ESABC validation dataset.

Embedded in the ENVISAT validation programme of the chemistry instruments GOMOS, MIPAS, and SCIAMACHY, a large number of balloon-borne, aircraft and ground-based measurements were carried out in the years 2002 and 2003 at various locations. Unfortunately, by the date of the ACVE-2 conference, re-analyzed operational MIPAS data was almost only available for the year 2002 limiting the number of validation cases with the new operational version 4.61 (v4.61) data significantly. Generally, the MIPAS HNO 3 profiles as processed with v4.61 are in good agreement with airborne observations in all cases with a good coincidence in time and space between the MIPAS observations and the correlative measurements. However, these validation cases have been confined so far to mid-latitudes only. Retrievals of MIPAS HNO 3 profiles as obtained by different processors appear to be generally rather robust as proven by a statistics of inter-comparisons of HNO 3 profiles between the operational v4.61 data and data processed with the IMK scientific processor. Ground-based correlative measurements based on the FTIR technique have been provided from different sites all over the world. Both column amounts and vertical profiles of HNO 3 with coarse resolution can be derived from such measurements. This data is potentially very useful for monitoring the longer term quality of MIPAS satellite data. However, the comparison of those columns amounts and profiles is not straightforward and a careful and consistent procedure needs to be applied to determine comparable values for the columns as well as to take into account the different vertical resolutions of the space-borne limb emission and the ground-based solar absorption measurements. Further validation coincidences in different geophysical situations have to be considered based on v4.61 data before a final quantitative assessment on the quality of the MIPAS operational HNO 3 data will become possible.

Embedded in the ENVISAT validation programme of the chemistry instruments GOMOS, MIPAS, and SCIAMACHY, a large number of balloon-borne, aircraft and ground-based measurements were carried out in the years 2002 and 2003 at various locations. Unfortunately, by the date of the ACVE-2 conference, re-analyzed operational MIPAS data was almost only available for the year 2002 limiting the number of validation cases with the new operational version 4.61 (v4.61) data significantly. Generally, the MIPAS HNO 3 profiles as processed with v4.61 are in good agreement with airborne observations in all cases with a good coincidence in time and space between the MIPAS observations and the correlative measurements. However, these validation cases have been confined so far to mid-latitudes only. Retrievals of MIPAS HNO 3 profiles as obtained by different processors appear to be generally rather robust as proven by a statistics of inter-comparisons of HNO 3 profiles between the operational v4.61 data and data processed with the IMK scientific processor. Ground-based correlative measurements based on the FTIR technique have been provided from different sites all over the world. Both column amounts and vertical profiles of HNO 3 with coarse resolution can be derived from such measurements. This data is potentially very useful for monitoring the longer term quality of MIPAS satellite data. However, the comparison of those columns amounts and profiles is not straightforward and a careful and consistent procedure needs to be applied to determine comparable values for the columns as well as to take into account the different vertical resolutions of the space-borne limb emission and the ground-based solar absorption measurements. Further validation coincidences in different geophysical situations have to be considered based on v4.61 data before a final quantitative assessment on the quality of the MIPAS operational HNO 3 data will become possible.

We report a preliminary validation of profiles from the MIPAS-Envisat on-line processor of ESA with correlative measurements derived from MIPAS-STR onboard the high-altitude aircraft M55-Geophysica. The validation is made for the 22 July 2002 orbit 2051 in the region of the campaign base in Forli, Italy. Profiles of HNO3 and O3 seem to agree well with the correlative measurements but vertical zigzag features, alternating for even and odd scans, are observed in the MIPAS profiles from Envisat. This behaviour, not observed by MIPAS-STR, is mostly pronounced in the CH4 and N2O data from channel B but also present in the temperature profiles derived from channel A. It is probably caused by deficiencies in the radiometric calibration of the atmospheric spectra which is independently performed for forward and backward interferometer sweeps.

The Russian high-altitude aircraft M-55 Geophysica has been deployed in several missions to obtain correlative measurements for the geophysical validation of the ENVISAT chemistry instruments MIPAS, SCIAMACHY and GOMOS. The payload of the Geophysica for the measurements of trace species was a unique combination of remote-sensing and in-situ instruments, enabling extensive Geophysica-internal intercomparisons. The correlative measurements were guided by forecasts of meteorological parameters (high-cloud coverage and gradients in the distributions of the atmospheric parameters) and by the expected time and location of the ENVISAT measurements. This paper gives an overview of the chemistry payload of the Geophysica, the deployments made at middle and high latitudes, the criteria for flight planning and the expected correlative data for ENVISAT validation.

Airborne measurements by MIPAS-STR (Michelson Interferometer for Passive Atmospheric Sounding-STRatospheric aircraft) during the APE-GAIA (Airborne Polar Experiment - Geophysica Aircraft In Antarctica) campaign were analysed. For phase correction of the interferograms and radiometric calibration specific schemes were applied to correct for beam splitter emission and atmospheric signatures in the deep space spectra. Characteristic features of the instrumental performance and auxiliary data needed for the retrieval are described. The retrieval of temperature along the flight track is shown for one selected day. These data are compared with independent in-situ measurements and global temperature analysis fields.

Test retrievals for the airborne limb- and upward sounder MIPAS-STR (Michelson Interferometer for Passive Atmospheric Sounding-STRatospheric aircraft) were performed. The influence of spectral noise and systematic errors was tested for a set of atmospheric trace gases. Downward error propagation from the unknown part of the profile above the aircraft and unresolved features in the reference profiles lead to deviations of the fit result even for the unperturbed retrievals. In cases of smooth profiles it was possible to retrieve the gradient up to some km above the Right level. Averaging kernels and test retrievals showed the possibility to increase the vertical resolution by oversampled measurements. However, a field-of-view (FOV) oversampling with respect to a vertical FOV extent larger than 1/2 does not seem to improve the results significantly.