Version 8 IMK/IAA MIPAS temperatures from 12–15 μm spectra: Middle and Upper Atmosphere modes

Abstract. Motivated by an improved ESA version of MIPAS calibrated spectra (version 8.03), we have released version 8 of MIPAS temperatures and pointing information retrieved from 2005–2012 MIPAS measurements at 12–15 μm in the Middle Atmosphere (MA), Upper Atmosphere (UA) and Noctilucent Cloud (NLC) measurement modes. The IMK/IAA retrieval processor in use considers non-local thermodynamic equilibrium (non-LTE) emission explicitly for each limb scan. This non-LTE treatment is essential to obtain accurate temperatures above the mid-mesosphere, because at the altitudes covered, up to 115 km, the simplified climatology-based non-LTE treatment employed for the nominal (NOM) measurements is insufficient. Other updates in MA/UA/NLC V8 non-LTE temperature retrievals from previous data releases include: more realistic atomic oxygen and carbon dioxide abundances; an updated set of spectroscopic data; an improved spectral shift retrieval; a continuum retrieval extended to altitudes up to 58 km; consideration of an altitude-dependent radiance offset retrieval; the use of wider microwindows above 85 km to capture the offset; an improved accuracy in forward model calculations; new temperature a priori information; improved temperature horizontal gradient retrievals; and, the use of MIPAS version 5 interfering species, where available. The resulting MIPAS MA/UA/NLC IMK/IAA temperature dataset is reliable for scientific analysis in the full measurement vertical range for the MA (18–102 km) and the NLC (39–102 km) observations, and from 42 to 115 km for the UA observations. The random temperature errors, dominated by the instrumental noise, are typically less than 1 K below 60 km, 1–3 K at 60–70 km, 3–5 K at 70–90 km, 6–8 K at 90–100 km, 8–12 K at 100–105 km and 12–20 K at 105–115 km. Pointing correction random errors, also mainly arising from instrumental noise, are on average 50 m for tangent altitudes up to 60 km and decrease linearly to values smaller than 20 m for altitudes above 95 km. The vertical resolution is 3 km at altitudes below 50 km, 3–5 km at 50–70 km, 4–6 km at 70–90 km, 6–10 km at 90–100 km and 8–11 km at 100–115 km. The systematic errors of retrieved temperatures below 75 km are driven by uncertainties in the CO₂ spectroscopic data and, above 80 km, by uncertainties in the non-LTE model parameters (including collisional rates and atomic oxygen abundance) and the CO₂ abundance. These lead to systematic temperature errors of less than 0.7 K below 55 km, 1 K at 60–80 km, 1–2 K at 80–90 km, 3 K at 95 km, 6–8 K at 100 km, 10–20 K at 105 km and 20–30 K at 115 km. Systematic errors in the tangent altitude correction, mainly arising from CO₂ spectroscopic uncertainties, are 250 m at 20 km and 200 m at 40–60 km, 100 m at 80 km and smaller than 50 m above 90 km. The consistency between the MA/UA/NLC and the NOM IMK/IAA datasets is excellent below 70 km (tyical 0.5–1 K differences). The comparison of this V8 temperature dataset with co-located SABER temperature measurements shows an excellent agreement, even better than in previous MIPAS IMK/IAA versions.