Odin/SMR Observations of Water Vapor and its Isotopes in the Middle Atmosphere

Water vapor, a strong greenhouse gas, plays an important role for the dynamics of the middle atmosphere. It is also linked to many chemical processes like the natural destruction of ozone (through the HO_x family). Improving our knowledge of the amount of water and its variability in the stratosphere and in the mesosphere is thus of primary importance. The Sub-Millimetre Radiometer (SMR) on board the Odin satellite, launched in February 2001, measures thermal emissions from the Earth's limb in the 485-580 GHz spectral range. In particular, a band around 489 GHz is used to study water vapor and its isotopes, on the basis of 4 observation days per month. Vertical profiles of H₂O-16, H₂O-18, and HDO are retrieved between roughly 20 and 70 km. In addition to the interesting picture of water vapor provided in the entire middle atmosphere, the unique and original measurements of HDO and H₂O-18 allow to study the isotopic depletion / enrichment of water, potentially supplying information on the origin of stratospheric water vapor: transport of tropospheric air through the tropical tropopause layer (TTL) vs in-situ chemical production by methane oxydation. The presentation aims to describe the global Odin/SMR dataset of H₂O, HDO, and the derived quantity δ D (H₂O). Particular emphasis is put on the variability seen during one year of analyzed observations. Odin is a Swedish-led satellite project funded jointly by Sweden, Canada, Finland and France.