Water vapour and methane are two of the target gases retrieved operationally in near-real-time (NRT) from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on Envisat. Water vapour and methane are chemically linked, since methane oxidation is the main source of water vapour in the stratosphere. The oxidation of methane eventually produces water vapour and molecular hydrogen such that the sum H2+H2O+2CH 4 is approximately constant with altitude. Assuming that the mixing ratio of molecular hydrogen is constant with altitude in the lower stratosphere, we would also expect the quantity H2O + 2CH4 to be reasonably constant in this region, providing a useful internal validation test. Here we assess the quality of water vapour and methane profiles from the ESA NRT retrieval, based on MIPAS data from July 2002 until March 2004. Monthly means of MIPAS profiles are used to examine differences from climatology, and look for any biases or long-term trends. Comparisons are also made with measurements from the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite (UARS).
