The isotopic composition of stratospheric water vapour depends on the sources of water vapour and the temperature and precipitation history of the stratospheric air. Isotopic measurements therefore have potential to aid invesigation of dehydration in the polar vortex, of stratospheric/tropospheric exchange, of upward transport in the tropics and of subsidence at polar latitudes. Here we compare measurements of H216O, HDO and H218O from two satellite limb-sounding instruments: the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), an infra-red limb sounder on Envisat, and the Sub-Millimetre Radiometer (SMR), a microwave limb sounder on board the Odin satellite.
