Vertical profile of δ¹⁸OOO from middle stratosphere to lower mesosphere derived by retrieval algorithm developed for SMILES spectra

Abstract

Abstract. Ozone is known to have large oxygen isotopic enrichments of about 10 % in the middle stratosphere, however, there have been no reports on ozone isotopic enrichments above the middle stratosphere. We derived an enrichment δ18OOO by a retrieval algorithm specified for the isotopic ratio from the stratosphere to the lower mesosphere based on observations from the Superconducting Submillimeter-Wave Limb–Emission Sounder (SMILES) onboard the International Space Station (ISS). The retrieval algorithm includes (i) an a priori covariance matrix constrained by oxygen isotopic ratios in ozone, (ii) an optimization of spectral windows for ozone isotopomers and isotopologues, and (iii) a common tangent height information for all windows. The δ18OOO obtained by averaging the SMILES measurements at the latitude range of 20° N to 40° N from February to March in 2010 with solar zenith angle <80° was 15% (at 32 km) and the systematic error was estimated to be about 5%. SMILES and past measurements were in good agreement with δ18OOO increasing with altitude between 30 and 40 km. The vertical profile of δ18OOO obtained in this study showed an increase and a decrease with altitude in the stratosphere and mesosphere, respectively. Stratopause is the peak-height of the δ18OOO value, and it rose to 18%. The δ18OOO has a positive correlation with temperature in the range of 220–255 K, indicating that temperature can be a dominant factor to control the vertical profile of δ18OOO in the stratosphere and mesosphere. This is the first report of the observation of δ18OOO over a wide range extending from the stratosphere to the mesosphere.