Heavy ozone enrichments from MIPAS limb emission spectra

Abstract. Vertical enrichment profiles of stratospheric heavy ozone (asymmetric and symmetric ⁵⁰O₃ isotopomers) have been derived from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). As a continuously operating satellite instrument, MIPAS has an advantage over previous measurements in providing global coverage over an extended time period, allowing the variations in enrichment to be determined. However, since the spectral features of the isotopomers are comparable with the magnitude of the instrument noise, a sequential estimation retrieval scheme has been used to average the measurements zonally.

The magnitude of observed enrichments is ~10% in stratosphere, a value consistent with previous observations and lab measurements. The data indicate that asymmetric heavy ozone is significantly more enriched than the symmetric isotopomer and show latitudinal and vertical variations in both the asymmetric and symmetric ⁵⁰O₃ enrichments. Enrichments decrease with decreasing temperature, as previously noted, at midlatidudes and polar regions, while they increase with decreasing temperature in equatorial regions.

MIPAS measurements contain also information on the asymmetric and symmetric ⁴⁹O₃ isotopomers. The enrichments of ⁴⁹O₃, obtained with the same sequential estimator approach, are much larger than the enrichments of ⁵⁰O₃, in contraddictions with previous results which predict larger enrichments for heavier isotopomers.