Column Amounts and Some Information on the Vertical Distribution of Trace Gases in the Late North Polar Winter 1990

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Abstract
During two field campaigns in the late north polar winter 1990, two Fourier transform infrared spectrometers were employed from the ground to investigate the chemical composition of the upper troposphere and stratosphere by determining zenith column amounts of the trace gases N2O, CH4, HCl, HF, HNO3, O3, and NO2. The spectrometers employed were the MIPAS (Michelson Interferometer for Passive Atmospheric Sounding), which was operating in Esrange, North Sweden (68°N, 21°E) from January 27 to March 31, 1990, and a modified BOMEM‐DA2, which was operating in Ny Aalesund, Spitsbergen (79°N, 12°E) from March 13 to April 24, 1990 with an unapodized spectral resolution of 0.015 cm−1 and 0.010 cm−1, respectively. From the interferograms, recorded by co‐adding during an integration time of less than 15 min, spectra were calculated by correction of the phase error and a standard Fourier transformation. Synthetic spectra were simulated using the SCAIS level‐by‐level and line‐by‐line algorithm and fitted to the measured ones by scaling the first guess mixing ratio profiles of the investigated gases. Model atmospheres for each day of measurement were built up from radiosonde data and ozone soundings and were used for the simulations. Finally, the gas amounts along the vertical path were integrated from the scaled profiles. Some information on the vertical distribution of the trace gases could be obtained from fitting the shapes of the spectral lines for N2O and HCl. Both the derived integrated zenith column amounts and the low resolved vertical distributions are interpreted in terms of dynamical as well as chemical processes. During the late winter 1990, periods of strongly perturbed stratospheric chemistry have been identified. Our results indicate evident similarities to ground based Antarctic measurements reported by other groups, but distinct differences regarding the behaviour of HNO3. Further understanding of the stratospheric situation is provided by an investigation of the time history of the air masses sampled with the help of the backward trajectory analysis.