Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 9 14 2009 10.5194/acp-9-5299-2009 http://www.atmos-chem-phys.net/9/5299/2009/ http://www.atmos-chem-phys.net/9/5299/2009/acp-9-5299-2009.html http://www.atmos-chem-phys.net/9/5299/2009/acp-9-5299-2009.pdf 5299 5319 2009-07-29 Evaluation of balloon and satellite water vapour measurements in the Southern tropical and subtropical UTLS during the HIBISCUS campaign N. Montoux A. Hauchecorne J.-P. Pommereau F. Lefèvre G. Durry R. L. Jones A. Rozanov S. Dhomse J. P. Burrows B. Morel H. Bencherif Laboratoire atmosphères, milieux, observations spatiales, Université Paris VI, CNRS, Verrières-le-Buisson, France Laboratoire de l'Atmosphère et des Cyclones, Université de la Réunion, CNRS, St-Denis de la Réunion, France Groupe de Spectroscopie moléculaire et Atmosphérique, Université de Reims Champagne-Ardenne, CNRS, Reims, France Center for Atmospheric Science, University Chemical Laboratory, University of Cambridge, Cambridge, UK Institute of Environmental Physics, University of Bremen, Bremen, Germany now at: the School of Earth and Environment, University of Leeds, UK Balloon water vapour in situ and remote measurements in the tropical upper troposphere and lower stratosphere (UTLS) obtained during the HIBISCUS campaign around 20° S in Brazil in February–March 2004 using a tunable diode laser (μSDLA), a surface acoustic wave (SAW) and a Vis-NIR solar occultation spectrometer (SAOZ) on a long duration balloon, have been used for evaluating the performances of satellite borne remote water vapour instruments available at the same latitude and measurement period. In the stratosphere, HALOE displays the best precision (2.5%), followed by SAGE II (7%), MIPAS (10%), SAOZ (20–25%) and SCIAMACHY (35%), all of which show approximately constant H2O mixing ratios between 20–25 km. Compared to HALOE of ±10% accuracy between 0.1–100 hPa, SAGE II and SAOZ show insignificant biases, MIPAS is wetter by 10% and SCIAMACHY dryer by 20%. The currently available GOMOS profiles of 25% precision show a positive vertical gradient in error for identified reasons. Compared to these, the water vapour of the Reprobus Chemistry Transport Model, forced at pressures higher than 95 hPa by the ECMWF analyses, is dryer by about 1 ppmv (20%). In the lower stratosphere between 16–20 km, most notable features are the steep degradation of MIPAS precision below 18 km, and the appearance of biases between instruments far larger than their quoted total uncertainty. HALOE and SAGE II (after spectral adjustment for reducing the bias with HALOE at northern mid-latitudes) both show decreases of water vapour with a minimum at the tropopause not seen by other instruments or the model, possibly attributable to an increasing error in the HALOE altitude registration. Between 16–18 km where the water vapour concentration shows little horizontal variability, and where the μSDLA balloon measurements are not perturbed by outgassing, the average mixing ratios reported by the remote sensing instruments are substantially lower than the 4–5 ppmv observed by the μSDLA. Differences between μSDLA and HALOE and SAGE II (of the order of −2 ppmv), SCIAMACHY, MIPAS and GOMOS (−1 ppmv) and SAOZ (−0.5 ppmv), exceed the 10% uncertainty of μSDLA, implying larger systematic errors than estimated for the various instruments. 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