Spaceborne ClO observations by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) before and during the Antarctic major warming in September/October 2002

Abstract

The first ClO profiles retrieved from limb emission spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) Fourier transform spectrometer on board the European research satellite ENVISAT (Environmental Satellite) are presented. These measurements were taken between 8 September and 13 October 2002. They cover the Antarctic major warming around 25 September, an event which had never been observed before. Since ClO has only weak signatures in the midinfrared, more than a dozen of the strongest lines, all situated in the central P branch and Q branch region of the 1‐0 band, were used for profile retrievals, which were based on constrained nonlinear least squares fitting. During the period of investigation, MIPAS measured typical ClO volume mixing ratios (vmrs) between 1 ± 0.4 and 2 ± 0.6 ppbv from 8 September until 23 September in contiguous parts of the dayside lower Antarctic stratosphere (400–625 K levels of potential temperature, Θ), i.e., before and at the beginning of the major warming. After 23 September no significant amounts of ClO were detected anymore, apart from some remains on 26 September. Daily averages of inside vortex daytime ClO showed a slight increase until about 17 September and a subsequent rapid ClO decrease. Further, a positive response of inside vortex nighttime ClO to increasing temperatures due to enhanced Cl2O2 dissociation was detected. Comparison with measurements of the Microwave Limb Sounder (MLS) on the Upper Atmospheric Research Satellite (UARS) from the years 1992–1997 generally showed a similar temporal development. Thus the warming event obviously happened too late to lead to a premature chlorine deactivation significantly different from previous Antarctic winters.