Improvement of Odin/SMR water vapour and temperature measurements and validation of the obtained data sets

Abstract. Its long photochemical lifetime makes H₂O a good tracer for mesospheric dynamics. Temperature is also an important tracer of seasonal circulation as well as multi-year trends. In this study we present the reprocessing of 18 years of mesospheric H₂O and temperature measurements from the Sub-Millimetre Radiometer (SMR) on board the Odin satellite, resulting in a part of the SMR version 3.0 level 2 data set. The previous version of the dataset showed poor accordance with measurements from other instruments, which suggested that the retrieved concentrations and temperature were subject to instrumental artifacts. Different hypotheses have been explored, and the idea of an underestimation of the single sideband leakage turned out to be the most reasonable one. The value of the lowest transmission achievable has therefore been raised to account for greater sideband leakage, and new retrievals have been performed with the new settings. The retrieved profiles extend between 40–100 km altitude and cover the whole globe to reach 85° latitudes. A validation study has been carried out, revealing an overall better accordance with the compared instruments. In particular, relative differences in H₂O concentration are always in the ±20 % range between 40 and 70 km and diverge at higher altitudes, while temperature absolute differences are within ± 5 K between 40–80 km (with the exception of FM13 SMR–MLS difference reaching almost 10 K) and also diverge at higher altitudes.