Comparisons between SCIAMACHY and ground-based FTIR data for total columns of CO, CH₄, CO₂ and N₂O

Total column amounts of CO, CH4, CO2 and N2O retrieved from SCIAMACHY nadir observations in ist near-infrared channels have been compared to data from a ground-based quasi-global network of Fourier-transform infrared (FTIR) spectrometers. The SCIAMACHY data considered here have been produced by three different retrieval algorithms, WFM-DOAS (version 0.5 for CO and CH4 and version 0.4 for CO2 and N2O), IMAP-DOAS (version 1.1 and 0.9 (for CO)) and IMLM (version 6.3) and cover the January to December 2003 time period. Comparisons have been made for individual data, as well as for monthly averages. To maximize the number of reliable coincidences that satisfy the temporal and spatial collocation criteria, the SCIAMACHY data have been compared with a temporal 3rd order polynomial interpolation of the ground-based data. Particular attention has been given to the question whether SCIAMACHY observes correctly the seasonal and latitudinal variability of the target species. The present results indicate that the individual SCIAMACHY data obtained with the actual versions of the algorithms have been significantly improved, but that the quality requirements, for estimating emissions on regional scales, are not yet met. Nevertheless, possible directions for further algorithm upgrades have been identified which should result in more reliable data products in a near future

The 2009 edition of the GEISA spectroscopic database

The updated 2009 edition of the spectroscopic database GEISA (Gestionet Etudedes Informations Spectroscopiques Atmospheriques ; Management and Study of Atmospheric Spectroscopic Information) is described in this paper. GEISA is a computer-accessible system comprising three independent sub-databases devoted, respectively, to: line parameters, infrared and ultraviolet/visible absorption cross-sections, microphysical and optical properties of atmospheric aerosols. In this edition, 50 molecules are involved in the line parameters sub-database, including 111 isotopologues, for a total of 3,807,997 entries, in the spectral range from 10-6 to 35,877.031cm-1. GEISA, continuously developed and maintained at LMD (Laboratoirede Meteorologie Dynamique, France) since 1976, is implemented on the IPSL/CNRS(France) ‘‘Ether’’ Products and Services Centre WEB site (http://ether.ipsl.jussieu.fr), where all archived spectroscopic data can be handled through general and user friendly associated managements of software facilities. More than 350 researchers are registered for online use of GEISA

Infrared Spectroscopic Measurements of the Vertical Column Abundance of Sulfur Hexafluoride, SF6, From the Ground

peer reviewedThe unresolved v3 band Q branch of sulfur hexafluoride, SF6, at 947.9 cm-1 has been identified and quantitatively analyzed in series of high-quality infrared solar spectra recorded at the International Scientific Station of the Jungfraujoch, Switzerland, and at the National Solar Observatory facility on Kitt Peak in Arizona. Series of monthly mean total vertical column abundances of SF6 above both stations, deduced from that feature with line-by-line nonlinear least squares fitting methods, are reported over the time intervals from June 1986 to June 1990 for the Jungfraujoch and from March 1981 to June 1990 for Kitt Peak. Assuming an exponential growth model for fitting these series of measurements, it is found that the vertical column abundances have increased at mean rates of 6.9 +- 2.8 %/yr above the Jungfraujoch (calculated columns of 2.99 x 10E13 molecules/cm2 in June 1986 and 3 94 x 10E13 molecules/cm2 in June 1990) and 6.6 +- 7.2 %/yr above Kitt Peak (calculated columns equal to 2.97 x 10E13 molecules/cm2 in June 1981 and 5.38 x 10E13 molecules/cm2 in June 1990), the uncertainties corresponding to 2 sigma confidence levels. These results are further discussed within the context of variability and compared with previously published measurements

Ground-Based Infrared Measurements of HNO3 Total Column Abundances: Long-Term Trend and Variability

The long-term trend and variability of the total column amount of atmospheric nitric acid (HNO3) have been investigated based on time series of infrared solar absorption spectra recorded at two remote high-altitude sites, the International Scientific Station of the Jungfraujoch (ISSJ) in the Swiss Alps (altitude 3.6 km, latitude 46.5°N, longitude 8.0°E) and the National Solar Observatory McMath solar telescope facility on Kitt Peak (altitude 2.1 km, latitude 31.9°N, longitude 111.6°W), southwest of Tucson, Arizona. The HNO3 v5 band Q branch at 879.1 cm-1 and three P branch manifolds near 869 cm-1 were analyzed using a nonlinear least squares spectral fitting technique and a consistent set of spectroscopic line parameters. The ISSJ measurements evaluated in the present work consist of two solar spectra recorded with a grating spectrometer in June 1951 and a set of observations obtained with a high-resolution Fourier transform spectrometer between June 1986 and June 1990. The modern ISSJ measurements show a ~20% peak-to-peak amplitude seasonal cycle with a winter maximum superimposed on significant variability and a summer minimum; the June results from 1986 to 1990 are both higher and lower than the two retrieved June 1951 HNO3 total column amounts. The fitted trend, (-0.16 +- 0.50) %/yr, 2 sigma, indicates that there has been no detectable change in the HNO3 total column over the last 4 decades. The Kitt Peak measurements, recorded with a high-resolution Fourier transform spectrometer between December 1980 and June 1990, also show marked variability in the HNO3 total column, but in contrast to the ISSJ measurements, no obvious seasonal cycle is observed. The deduced trend in the total column above Kitt Peak, (-0.8 +- 1.6) %/yr, 2 sigma, is consistent with the ISSJ time series of measurements, in that no significant HNO3 long-term trend has been found. The sets of measurements from the two sites are compared with each other and with previously published results, with emphasis on the reported variability of HNO3 and the changes in the HNO3 total column with season and latitude

Determination of Absolute Strengths of N2 Quadrupole Lines From High-Resolution Ground-based IR Solar Observations

High-resolution, high signal-to-noise ratio, solar absorption spectra recorded with a Fourier transform spectrometer at the International Scientific Station of the Jungfraujoch, Switzerland, have been analyzed to determine the strengths of several lines belonging to the S branch of the N2 (1-0) electric quadrupole vibration-rotation band centered at 2329.9168 cm-1. The method which was applied here was based on equivalent width measurements of lines observed over a broad range of air masses; extrapolation of these measurements to zero air mass gave the line strengths for the transitions S7 to S10, independent of half widths, an ambiguity unavoidable with the use of curve-fitting techniques. The resulting absolute accuracies of the line strengths derived here, estimated to be better than +-2.5% for S8, +-2.6% for S10, +-3.4% for S9, and +-5.1% for S7, are due largely to the high quality and quantity of the spectra retained in this analysis and the accuracy with which the observation conditions are known. An important application of the improved values for these N2 transitions, which have low initial ground state energies, is the direct determination of the line-of-sight atmospheric air masses associated with remotely sensed infrared spectroscopic observations. Positions of the N2 transitions studied here have further been redetermined with an absolute accuracy better than 0.0002 cm-1

Remote sensing of the atmosphere by high resolution infrared absorption spectroscopy

peer reviewe

Seasonal Cycle and Secular Trend of the Total and Tropospheric Column Abundance of Ethane Above the Jungfraujoch

Total column abundances of ethane (C2H6) above the Jungfraujoch Station, Switzerland, 3.58-km altitude, have been deduced from infrared solar spectra recorded in 1951 and from 1984 to 1988. The results were derived from the spectroscopic analysis of the v7 band PQ3, PQ1, and RQ0 subbranches of C2H6 near 2976.8, 2983.4, and 2986.7 cm-1, respectively. The 1984-1988 results obtained from more than 300 observations at 0.005 cm-1 resolution show a definite seasonal variation in the total vertical column abundance of that gas, with a maximum of (1.43 +- 0.03) x 10E16 molecules/cm2 during March and April and a minimum in the fall. The corresponding C2H6 mixing ratio in the free troposphere was derived to 1.53 +- 0.14 ppb in early April; the ratio of maximum to minimum C2H6 concentration in the troposphere was found to be 1.88 +- 0.12. From the analysis of the same spectral features observed in March and April 1951, we have deduced a total vertical column abundance of (1.09 +- 0.10) x 10E16 molecules/cm2. Assuming an exponential increase with time and correcting for a small decrease in the stratospheric amount of C2H6 due to the man-induced increase in stratospheric chlorine, we obtain a secular trend in the tropospheric burden above the Jungfraujoch equal to (0.85 +- 0.3)%/yr. It is argued that this trend is valid for the entire northern hemisphere