F. Friedl-Vallon

Design and characterization of the balloon-borne Michelson Interferometer for Passive Atmospheric Sounding (MIPAS-B2)

MIPAS-B2 is a balloon-borne limb-emission sounder for atmospheric research. The heart of the instrument is a Fourier spectrometer that covers the mid-infrared spectral range (4-14 microns) and operates at cryogenic temperatures. Essential for this application is the sophisticated line-of-sight stabilization system, which is based on an inertial navigation system and is supplemented with an additional star reference system. The major scientific benefit of the instrument is the simultaneous detection of complete trace gas families in the stratosphere without restrictions concerning the time of day and viewing directions. The specifications, the design considerations, the actual realization of the instrument, and the results of characterization measurements that have been performed are described.

Stratospheric ClONO2 and HNO3 profiles inside the Arctic vortex from MIPAS‐B limb emission spectra obtained during EASOE

Vertical profiles of ClONO2 and HNO3 inside the Arctic vortex have been retrieved from infrared limb emission spectra recorded during balloon flights on January 13 and in the night of March 14/15, 1992 from Esrange, Sweden (68°N) as part of the European Arctic Stratospheric Ozone Experiment (EASOE). The instrumentation used was the cryogenic Michelson Interferometer for Passive Atmospheric Sounding, Balloon-borne version (MIPAS-B). Low ClONO2 abundances in mid-January indicate that a significant portion of ClONO2 had already been converted at that time. An unexpectedly high ClONO2 amount (1.8 to 3.1 ppbv between 16.1 and 21.5 km altitude) has been inferred from the March flight data. This implies that obviously most of the total available chlorine (ClOy) in the lower stratosphere was then in this reservoir molecule. The measured HNO3 profiles give no hint of any significant layered removal of gaseous HNO3 by condensation on particles or/and sedimentation.

Retrieval of stratospheric O3, HNO3 and ClONO2 profiles from 1992 MIPAS-B limb emission spectra: Method, results, and error analysis

Within the framework of the European Arctic Stratospheric Ozone Experiment, two flights of the balloon-borne MIPAS-B limb emission spectrometer were performed in the Arctic stratosphere from Kiruna, northern Sweden. During the early hours of January 13 and the night from March 14 to March 15, 1992, several limb sequences of infrared spectra were recorded which have permitted the retrieval of vertical profiles of many trace gases relevant for ozone chemistry. In the present work, the retrieval strategy, error estimation strategy, and resulting profiles of O3, HNO3, and ClONO2 are reported. The data analysis procedure, consisting of data preprocessing including calibration, analysis of auxiliary data including temperature profiles and line of sight determination, and retrieval of trace gas profiles, is described in detail. The last is carried out by means of multiparameter nonlinear least squares fitting in combination with onion peeling. An astonishingly high ClONO2 amount of 2.6 ppb by volume at about 19-km altitude was inferred for the March flight. A rigorous error analysis, which takes into account systematic and random errors and their often nonlinear impact on the results, proves the significance of the retrieved trace gas profiles.

NOy partitioning and budget and its correlation with N2O in the Arctic vortex and in summer midlatitudes in 1997

Vertical profiles of the most important species of nocturnal total reactive nitrogen (NO y = NO 2 + HNO 3 + CIONO 2 + 2 N 2 O 5 + HO 2 NO 2 ) together with its source gas N 2 O were retrieved from infrared limb emission spectra measured by the Michelson Interferometer for Passive Atmospheric Sounding, Balloon-borne version (MIPAS-B) instrument inside the late winter arctic vortex from Kiruna (Sweden, 68°N) on 24 March 1997 and in summer midlatitudes from Gap (France, 44°N) on 2 July 1997. The measured data were compared to calculations performed with the three-dimensional chemistry transport model (CTM) Karlsruhe Simulation model of the Middle Atmosphere (KASIMA). The results show that in the late winter arctic vortex most of the available nitrogen and chlorine is in the form of HNO 3 and CIONO 2 , respectively. An anomalous N 2 O-NO y correlation observed in March 1997 appears to be caused to a large extent by quasi-horizontal mixing of air masses across the vortex edge. However, near 20 km some denitrification of ∼1.5 to 2 ppbv NO y could be observed. The N 2 O profile measured in July 1997 indicates remnants of polar vortex air and is not reproduced by the CTM at the same location. However, the profile shapes of the individual compounds of the NO y family as well as the NO x /NO y ratio are reproduced fairly well by the model.

Determination of the stratospheric organic chlorine budget in the spring arctic vortex from MIPAS B limb emission spectra and air sampling experiments

Vertical profiles of halogenated source gases, CF 2 Cl 2 , CFCl 3 , CHF 2 Cl, Cl 4 , and CF 4 , were retrieved from limb emission spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding, Balloonborne version (MIPAS B) during a balloon flight launched from Esrange near Kiruna, northern Sweden (68°N) on March 14, 1992. This flight was a contribution to the balloon launch program of the European Arctic Stratospheric Ozone Experiment (EASOE) campaign. All problems encountered during the analysis of the recorded spectra are discussed in detail. These are primarily the lack of spectral data for HNO 3 which interferes with the CF 2 Cl 2 ν 6 band, and the strong effects attributed to the Pinatubo aerosol. As the air mass sounded by MIPAS was polar vortex air, these data supplement the results of in situ air sampling experiments, which investigated air masses outside or at the edge of the polar vortex at altitudes below 18 km during the last phase of EASOE. An analysis is made of the vertical profiles of the seven most abundant organic chlorine species (CF 2 Cl 2 , CFCl 3 , CHF 2 Cl, CCl 4 , CH 3 Cl, CH 3 CCl 3 , and C 2 F 3 Cl 3 ) during that phase of the EASOE campaign. Mixing ratios of those organic chlorine compounds which had not been measured by MIPAS are inferred from profiles provided by air sampling experiments performed between November 30, 1991, and March 12, 1992. These profiles were adjusted to the dynamic conditions during the MIPAS observations, namely the effect of subsidence, using CF 2 Cl 2 as a tracer. This allowed to derive the relative contributions of the organic chlorine species to the total chlorine budget of the air mass sounded by MIPAS. The results are consistent with the high ClONO 2 mixing ratio of 2.6 parts per billion by volume (ppbv) observed at 18.9-km altitude during this flight of MIPAS B.

Simultaneous measurements of HDO, H2O, and CH4 with MIPAS‐B: Hydrogen budget and indication of dehydration inside the polar vortex

For the first time, vertical profiles of HDO inside the Arctic vortex along with CH4 and H2O were retrieved from nighttime infrared limb emission spectra measured by the Michelson Interferometer for Passive Atmospheric Sounding, Balloonborne instrument (MIPAS-B) from Kiruna (Sweden, 68°N) on February 11, 1995 and March 24, 1997. The deuterium to hydrogen ratio (D/H) of water vapor shows a strong depletion in comparison to that of standard mean ocean water (SMOW), particularly in the lower stratosphere for the February 1995 flight. This extraordinarily strong depletion indicates an additional isotopic effect due to dehydration by polar stratospheric cloud particles. The maximum dehydration occurs at a lower altitude than that of the denitrification measured on the same flight. A dehydration of up to 0.7(±0.4) ppmv is seen in the compact correlation between CH4 and H2O. For the March 1997 results the exceptionally low D/H ratios and a deviation from the linear H2O-CH4 correlation could not be found. The H2O results of the February 1995 flight show a peak mixing ratio of 7.1 ppmv at 17.1 hPa and a minimum of 3.6 ppmv at 137.5 hPa. The analysis of the March flight shows a similar profile, but the vertical gradient is less pronounced. The total hydrogen budget of the stratosphere was examined by evaluating the quantity [H] = [H2O] + 2[CH4], revealing values of around 7.25 ppmv on average for both flights. All profiles reflect the subsidence of polar vortex air.

ClONO2 vertical profile and estimated mixing ratios of ClO and HOCl in winter Arctic stratosphere from Michelson interferometer for passive atmospheric sounding limb emission spectra

Nighttime limb emission spectra recorded by the balloon-borne Michelson interferometer for passive atmospheric sounding (MIPAS) on February 11, 1995, near Kiruna were used to infer a vertical profile of ClONO2 as well as estimates of ClO and HOCl volume mixing ratios. The highest ClONO2 mixing ratio (2.6 parts per billion by volume (ppbv)) was found at 22.69 km altitude and is explained by an early recovery of this chlorine reservoir in the upper part of the formerly chlorine-activated height range. Inferred nighttime ClO mixing ratios appear to be rather high for the lower stratosphere (0.38 ppbv at 16.43 km altitude) and indicate chlorine activation at this altitude region. The HOCl mixing ratio is estimated as 0.03 ppbv at 28.04 km altitude, while for lower altitudes the HOCl concentrations are clearly below the detection limit of MIPAS. The measurements are compared with three-dimensional chemical transport model calculations. Results agree reasonably well but show differences in detail.

Vertical profiles of N2O5, HO2NO2, and NO2 inside the Arctic vortex, retrieved from nocturnal MIPAS-B2 infrared limb emission measurements in February 1995

Vertical profiles of N 2 O 5 , HO 2 NO 2 , and NO 2 inside the arctic vortex were retrieved from nighttime infrared limb emission spectra measured by the Michelson Interferometer for Passive Atmospheric Sounding, Balloon-borne version 2 (MIPAS-B2) instrument from Kiruna (Sweden, 68°N) on February 11, 1995, as part of the Second European Stratospheric Arctic and Midlatitude Experiment (SESAME). Spectra were analyzed by a multiparameter nonlinear least squares fitting procedure in combination with an onion-peeling retrieval algorithm. The N 2 O 5 , HO 2 NO 2 , and NO 2 results were derived from spectral features within the bands near 8.0 μm, 12.5 μm, and 6.2 μm, respectively. Peak mixing ratios of 1.14 parts per billion by volume (ppbv) N 2 O 5 and 80 parts per trillion by volume (pptv) HO 2 NO 2 at 17.1 hPa as well as 2.79 ppbv NO 2 at 12.0 hPa corresponding to 25.8 km and 28.0 km altitude were inferred from the spectra. NO 2 mixing ratios measured by MIPAS fit well to the data observed by concurrent flights. A comparison with calculations performed with a three-dimensional chemistry transport model for the time and location of the measurements shows that the best agreement of measured and calculated profiles is reached between 17 and 28 hPa corresponding to 25.8 and 22.7 km altitude, while below and above this altitude region there are some discrepancies between the modeled and observed data.

Balloonborne Michelson interferometer for passive atmospheric sounding (MIPAS-B2): instrument and results

MIPAS-B2 is a cryogenic limb-sounder dedicated to stratospheric trace gas research. The balloon borne instrument is a precursor of the MIPAS instrument on the ESA ENVISAT satellite. In consequence, the main instrumental specifications and parameters are similar. The instrument has been flown several times successfully in the frame of European atmospheric research campaigns (SESAME and THESEO) and a satellite validation campaign (ILAS). The heart of the instrument is a Fourier spectrometer working in the mid- infrared range (4 to 14 micrometer), which is cooled before launch to its operating temperature of 210 K with solid carbon dioxide. The spectral coverage is split into four spectral channels to improve sensitivity in particular in the short wavelength region. We employ liquid helium cooled Si:As-BIB- detectors to achieve optimum detectivity. A further important part of the instrument is the line of sight (LOS) stabilization system, which is based on an inertial navigation system and can be cross-examined with the help of an additional star reference system. The instrument was flown eight times from balloon launch sites in Sweden and France. The recorded data allowed the retrieval of many trace gases. One major scientific advantage of the instrument is the simultaneous detection of whole trace gas families in the stratosphere. All relevant night-time NOy species (NO2, N2O5, HNO3, ClONO2 and HO2NO2) together with the source gas N2O were successfully analyzed.

Intercomparison of ILAS/ADEOS with MIPAS-B measurements in late March 1997

Embedded in the ILAS validation campaign a balloon flight was carried out with the limb emission sounder MIPAS-B in the early night of March 24, 1997. MIPAS-B is capable is capable of simultaneously measuring profiles of all molecules ILAS was covering. Key reservoir molecules like ClONO2 and N2O25 which are not or hard to measure with ILAS complement the ILAS set of target species and allow the partitioning and budge to NOy to be studied. The balloon was launched from Kiruna/Sweden. The distance of the mean location of tangent points between the satellite and the balloonborne observation was less than 150 km and the time was offset by less then 4 hours for the most adjacent overpass of ADEOS. The balloon observations covered the altitude range of 11.0 to 29.5 km. Vertical profiles of N2O, CH4, H2O, HNO3 NO2 and aerosol extinction obtained with MIPAS-B have been compared to those obtained with ILAS based on the three most adjacent ADEOS overpasses. Model calculations with the 3D chemical transport model KASIMA were used to account for nay deviations in the dynamical and chemical properties of the airmasses observed at the different times and locations of observation. The paper demonstrates the progress made in the consistency of the data sets when going from Version 3.0 to Version 3.1 of the ILAS data processing software. Excellent agreement between balloon and satellite observation has been found for HNO3 on the basis of the Version 3.1 results. The same holds for NO2 above 20 km provided the diurnal variation is taken into account. Discrepancies still exist with the Version 3.1 results in the lowermost part of the stratospheric for most gases and generally in the case of N2O.