MIPAS ozone retrieval version 8: middle atmosphere measurements

Abstract. We present a new version of O₃ data retrieved from the three MIPAS observations modes of the middle atmosphere (MA, UA and NLC). The O₃ profiles cover altitudes from 20 up to 100 km altitudes for daytime and up to 105 km at nighttime, for all latitudes, and the period 2005 until 2012. The data has been obtained with the IMK–IAA MIPAS level 2 data processor and are based on ESA version 8 re-calibrated radiance spectra with improved temporal stability. The processing included several improvements with respect to the previous version, such as the consistency of the microwindows and spectroscopic data with those used in the nominal mode V8 data, the O₃ a priori profiles, and updates of the non-LTE parameters and of the nighttime atomic oxygen. Random errors are dominated by the measurement noise with 1σ values for single profiles for daytime of <5 % below ~60 km, 5–10 % between 60 and 70 km, 10–20 % at 70–90 km and about 30 % at 95 km. For nighttime, they are very similar below 70 km but smaller above (10–20 % at 75–95 km, 20–30 % at 95–100 km and larger than 30 % above 100 km). The systematic error is ~6 % below ~60 km (dominated by uncertainties in spectroscopic data), and 8–12 % above ~60 km, mainly caused by non-LTE uncertainties. The systematic errors in the 80–100 km range are significantly smaller than in the previous version. The major differences with respect to the previous version are: 1) The new retrievals provide O₃ abundances in the 20–50 km altitude range larger by about 2–5 % (0.2–0.5 ppmv); 2) O₃ abundances reduced by ~2–4 % between 50 and 60 km in the tropics and mid-latitudes; 3) reduced O₃ abundances in the nighttime O₃ minimum just below 80 km, leading to a more realistic diurnal variation; 4) larger daytime O₃ concentrations in the secondary maximum at the tropical and mid-latitudes (~40 %, 0.2–0.3 ppmv); and 5) nighttime O₃ abundances in the secondary maximum reduced by 10–30 %. The O₃ profiles retrieved from the nominal mode (NOM) and the middle atmosphere modes are fully consistent in their common altitude range (20–70 km). Only at 60–70 km daytime O₃ of NOM seems to be larger than that of MA/UA by 2–10 %. Compared to other satellite instruments, MIPAS seems to have a positive bias of 5–8 % below 70 km. Noticeably, the new version of MIPAS agrees much better than before with all instruments in the upper mesosphere/lower thermosphere, reducing the differences from ~ ±20 % to ~ ±10 %. Further, the diurnal variation of O₃ in the upper mesosphere (near 80 km) has been significantly improved.