Ginette Roland

Observed trends in total vertical column abundances of atmospheric gases from IR solar spectra recorded at the Jungfraujoch

Since 1984, about 15000 high quality infrared solar spectra have beenrecorded with state-of-the-art grating and Fourier transform spectrometersat the International Scientific Station of the Jungfraujoch, Switzerland.Nonlinear least squares spectral curve fitting of selected microwindowscontaining isolated and well characterized lines of 20 telluric gases haveallowed to retrieve their total vertical column abundances above thestation, leading to observational data bases essential to derive long- andshort-term changes experienced by these species during the last 12 years. Inthis paper, we focus on atmospheric gases of particular interest within thecontext of the EUROTRAC/TOR (Tropospheric Ozone Research) project; secularevolution as well as seasonal cycles of the minor constituentsCH4, CO and of the trace gasesC2H6, OCS, C2H2, HCNand H2CO are reported and discussed. The long-livedN2O is included as a tracer of the dynamic activity of theatmosphere.

Vertical column abundances of HCN deduced from ground-based infrared solar spectra: long-term trend and variability

A set of high-resolution IR solar spectra recorded at the International Scientific Station of the Jungfraujoch, Switzerland, from 84/06 to 93/06, and at the National Solar Observatory McMath-Pierce solar telescope facility on Kitt Peak, Arizona, U.S.A. from 78/05 to 92/07 have been analyzed to determine the vertical column abundances of hydrogen cyanide, HCN, above the two stations. The analysis was based on least-squares curve fitting of calculated spectra to the observations encompassing the P4 and the P8 lines of HCN respectively located at 3299.5273 and 3287.2483 cm−1. The results obtained for the two stations indicate that no significant long-term trend affects either of the two databases; however, this analysis reveals variable increases during springtime of up to a factor of 2 in the HCN total column above the Jungfraujoch and even up to 3 above Kitt Peak. The calculated mean vertical column abundances, excluding the spring observations, are equal to (2.55±0.30)×1015 molec./cm2 (S.D.) and (2.75±0.30)×1015 molec./cm2 respectively above the Jungfraujoch and the Kitt Peak observatories. Based on a realistic volume mixing ratio profile, these columns translate into mean volume mixing ratios equal to 190×10−12 ppv at the respective altitudes of the stations.

Monitoring of the integrated column of hydrogen fluoride above the Jungfraujoch Station since 1977 ― the HF/HCL column ratio

The amount of hydrogen fluoride (HF) above the International Scientific Station of the Jungfraujoch (Switzerland) has been monitored during the last 8 years. The results deduced spectro-scopically from solar IR absorption measurements near 2.48 μm indicate a cumulative trend equivalent to (8.5±1)% increase per year, as well as short-term variability which appears to be strongly correlated with meridional circulation patterns during the February–April months. Based on intensified measurements made over the last three years, it is found that the integrated content of HF undergoes a seasonal change with a minimum occurring in the fall. The HF/HCl ratio derived from simultaneous HF and HCl measurements was found equal to 0.15 during the period 1977–79, and 0.24 for the 1983–85 timespan.

Column abundance and the long-term trend of hydrogen chloride (HCl) above the Jungfraujoch station

The integrated column amount of hydrogen chloride has been monitored above the International Scientific Station of the Jungfraujoch (Switzerland) during the last 8 years. The results deduced from solar absorption measurements near 3.42 μm indicate a secular trend equivalent to (0.75±0.2) % increase per year since 1978, superimposed on a significant short-term variability which can be partly attributed to the tropospheric component of the total HCl burden. Based on an intensified set of measurements carried out over the last three years, a seasonal component in the total content of HCl has been established for the first time, showing a minimum occuring in early winter and a maximum during the spring.

Balloon Intercomparison Campaigns: Results of remote sensing measurements of HCl

All of the techniques used to measure stratospheric HCl during the two BIC campaigns involved high resolution infrared spectroscopy. The balloon-borne instruments included five different spectrometers, three operating in the solar absorption mode and two in emission (at distinctly different wavelengths). Ground-based and aircraft correlative measurements were made close to the balloon locations, again by near-infrared spectroscopy.Within this set of results, comparisons between different techniques (absorption vs emission) viewing the same airmass (i.e., on the same gondola) were possible, as were comparisons between the same technique used on different gondolas spaced closely in time and location. The final results yield a mean profile of concentration of HC1 between 18 and 40 km altitude; an envelope of ±15% centered on this profile encompasses all of the results within one standard deviation of their individual mean values. The absolute accuracy of the final profile is estimated to be no worse than 10%. It is concluded also that the measurement techniques for HCl have reached a level of performance where a precision of 10% to 15% can be confidently expected.

Quantitative evaluation of the post-Mount Pinatubo NO2 reduction and recovery, based on 10 years of Fourier transform infrared and UV-visible spectroscopic measurements at Jungfraujoch

The colocation of two technically different instruments for ground-based remote sensing of NO2 total column amounts at the primary Network for the Detection of Stratospheric Change Alpine station of the Jungfraujoch (46.5°N, 8.0°E) has been exploited for mutual validation of the long-term NO2 time series from both instruments and for a quantitative evaluation of the impact of the Mount Pinatubo eruption on the NO2 abundance above this northern midlatitude observatory. The two techniques are high-resolution Fourier transform infrared solar absorption spectrometry and zenith-sky differential optical absorption spectroscopy in the UV visible. The diurnal variation of NO2 has been simulated by a simple photochemical model that allows a comparison between the data from the two techniques. This model is shown to reproduce the observed morning to evening ratios to 2.3%, on average, which is fully adequate for the needs of this study. From the 1985–1996 combined time series of NO2 morning and evening abundances, it has been concluded that the enhanced aerosol load injected into the stratosphere by Mount Pinatubo caused a maximum NO2 reduction above the Jungfraujoch by 45% in early January 1992 that died out quasi-exponentially to zero by the beginning of 1995.

Evolution of a dozen non-CO2 greenhouse gases above central Europe since the mid-1980s

Abstract High-resolution infrared solar observations have been conducted consistently since the mid-1980s at the International Scientific Station of the Jungfraujoch, Switzerland, by the GIRPAS-ULg team (Groupe Infra-Rouge de Physique Atmosphérique et Solaire-University of Liège), and by colleagues from the Belgian Institute for Space Aeronomy and from the Royal Observatory of Belgium, Brussels. These observations were performed with state-of-the-art Fourier transform infrared (FTIR) spectrometers, revealing specific absorption features of over 20 atmospheric gases in the middle-infrared. Related spectrometric analyses have allowed the derivation of their burdens, seasonal and inter-annual variability, as well as their long-term evolution. In addition to updates of long-term changes for CCl2F2, CHClF2, CH4, N2O, SF6, CO, C2H6 and C2H2 already dealt with at previous Non-CO2 Greenhouse Gases (NCGG) symposia, this paper further reports temporal evolutions observed during the past two decades for a series of other source gases, namely OCS, HCN, CCl3F and CCl4, which also have direct or indirect effects on the radiation balance of the troposphere and on the stratospheric ozone layer.

Intercomparison of measurements of stratospheric hydrogen fluoride

Observations of the vertical profile of hydrogen fluoride (HF) vapor in the stratosphere and of the vertical column amounts of HF above certain altitudes were made using a variety of spectroscopic instruments in the 1982 and 1983 Balloon Intercomparison Campaigns. Both emission instruments working in the far infrared spectral region and absorption instruments using solar occultation in the 2.5μm region were employed. No systematic differences were seen in results from the two spectral regions. A mean profile from 20–45 km is presented, with uncertainties ranging from 20% to 50%. Total columns measured from ground and from 12 km are consistent with the profile if the mixing ratio for HF is small in the tropophere and low stratosphere.

Intercomparison of stratospheric NO2 and NO3 measurements during MAP/GLOBUS 1983

Abstract Nitrogen dioxide and trioxide have been observed from balloons, plane and from the ground during MAP/GLOBUS 1983. Comparison between NO2 mixing ratios measured from balloons shows some agreement between remote sensing techniques on the one hand and in situ methods on the other. The two sets of data which agree in the lower stratosphere at 20 km diverge at higher altitudes by a factor of 2 around 27 km and 4 around 33 km. The NO2 column densities observed at sunset from the ground are in agreement with plane and balloon determinations, provided that the average mixing ratio below 16 km was indeed lower than 1.5 × 10−10. The diurnal variation of the NO2 column as determined from ground observations during the second half of September differs from the one seen in the stratosphere. A first comparison between NO3 night-time remote measurement and preliminary in situ results show a disagreement by a factor of 2.

High-resolution solar and atmospheric spectroscopy from the Jungfraujoch high-altitude station

Since 1958, the University of Liege (Belgium) has been maintaining a laboratory at the Jungfraujoch International Scientific Station, in the Swiss Alps, at an altitude of 3580 m. Equipped with two high-performance Fou rier-transform spectrometers, this laboratory is devoted to the study of the solar spectrum in the visible and in the infrared, at very high resolution. Its first objective was to improve the knowledge of the chemical composition of the suns outer layers, but since 1977 interest has moved progressively towards atmospheric research. The Jungfraujoch laboratory is now one of the primary stations of an international network to monitor the changes in the abundances of various constituents of the Earths upper atmosphere.