G. Maucher

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.

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.

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.

First results of ground‐based FTIR measurements of atmospheric trace gases in north Sweden and Greenland during EASOE

Zenith column amounts of N2O, CH4, CFC-12, O3, HNO3, ClONO2, HCl, and HF were measured by ground-based FTIR spectrometers at Kiruna in November 1991 and from January to March 1992, and in January and March 1992 in Sondre Stromfjord, Greenland. They were correlated to the dynamical situation of the stratosphere and interpreted in terms of chemical processes, with respect to the position of the vortex, the stratospheric temperatures, and the trajectories of the air masses for the last ten days. One of the most remarkable results is the increasing ClONO2 burden from the end of January to mid-March, reaching the extremely high value of 7.2 × 1015 molec./cm².

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.

Sequestration of HNO3 in polar stratospheric clouds and chlorine activation as monitored by ground-based Fourier transform infrared solar absorption measurements

Solar absorption infrared spectra measured with the ground-based Michelson Interferometer for Passive Atmospheric Sounding-Laboratory Model (MIPAS-LM) at the Esrange research station near Kiruna, North Sweden, were analyzed for zenith column amounts of stratospheric trace gases. Time series of HF, HCl, ClONO 2 , HNO 3 , and O 3 measured in the winter of 1991-1992, the summer of 1992, and the winter of 1992-1993 were studied for anomalies indicating a perturbed stratospheric chemistry in the Arctic winter. Indications of chlorine activation were found in both winters, inside the stratospheric polar vortex as well as at the vortex edge, as was indicated by the ratio of stratospheric HCI to the HF zenith column amount. This ratio decreased from values higher than 3 for chemically undisturbed stratospheric conditions to 1.1 - 1.3 in January 1992 and 0.8 in February 1993, inside the polar vortex when maximum chlorine activation took place. Sequestration of HNO 3 in polar stratospheric clouds (PSCs) was found on several days of observation inside the polar vortex; it leads to a decrease of the HNO 3 zenith column amounts by up to 50% on February 10, 1993. From comparison to model calculations we conclude that the HNO 3 loss can only be explained by formation of nitric acid trihydrate (NAT) PSCs on January 18, 1992, and February 10, 1993, whereas on January 19, 1992, January 28, 1993, and February 11, 1993, the formation of ternary solutions can also explain the HNO 3 loss.

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.

The new balloon-borne MIPAS-B2 limb emission sounder

The new MIPAS-B2 (Michelson Interferometer for Passive Atmospheric Sounding-Balloon Version 2) instrument is a cryogenic infrared spectrometer mounted in a stratospheric balloon gondola and equipped with suitable subsystems to efficiently allow limb emission sounding of stratospheric trace gases. The instrument has been improved in various aspects compared to its predecessor, special emphasis has been laid on a high performance pointing system. The instrument had two sucessful flights from Esrange, Kiruna, Sweden during the third phase of the SESAME-campaign in February and March 1995.