Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 7 5 2007 10.5194/acp-7-1471-2007 http://www.atmos-chem-phys.net/7/1471/2007/ http://www.atmos-chem-phys.net/7/1471/2007/acp-7-1471-2007.html http://www.atmos-chem-phys.net/7/1471/2007/acp-7-1471-2007.pdf 1471 1489 2007-03-19 Mesoscale modelling of water vapour in the tropical UTLS: two case studies from the HIBISCUS campaign V. Marécal virginie.marecal@cnrs-orleans.fr G. Durry K. Longo S. Freitas E. D. Rivière M. Pirre Laboratoire de Physique et Chimie de l'Environnement, CNRS and Université d'Orléans, 3A Avenue de la Recherche Scientifique, 45071 Orléans cedex 2, France Groupe de Spectroscopie Moléculaire et Atmosphérique, CNRS and Université de Reims, Moulin de la Housse, B.P. 1039, 51687 Reims Cedex, France Service d'Aéronomie, CNRS and Institut Pierre Simon Laplace, 91371 Verrières-le-Buisson Cedex, France Centro de Previsão de Tempo e Estudos Climàticos, Rodovia Presidente Dutra, km 40 SPRJ 12630-000, Cachoeira Paulista – SP, Brazil In this study, we evaluate the ability of the BRAMS (Brazilian Regional Atmospheric Modeling System) mesoscale model compared to ECMWF global analysis to simulate the observed vertical variations of water vapour in the tropical upper troposphere and lower stratosphere (UTLS). The observations are balloon-borne measurements of water vapour mixing ratio and temperature from micro-SDLA (Tunable Diode Laser Spectrometer) instrument. Data from two balloon flights performed during the 2004 HIBISCUS field campaign are used to compare with the mesoscale simulations and to the ECMWF analysis. The observations exhibit fine scale vertical structures of water vapour of a few hundred meters height. The ECMWF vertical resolution (~1 km) is too coarse to capture these vertical structures in the UTLS. With a vertical resolution similar to ECMWF, the mesoscale model performs better than ECMWF analysis for water vapour in the upper troposphere and similarly or slightly worse for temperature. The BRAMS model with 250 m vertical resolution is able to capture more of the observed fine scale vertical variations of water vapour compared to runs with a coarser vertical resolution. This is mainly related to: (i) the enhanced vertical resolution in the UTLS and (ii) to the more detailed microphysical parameterization providing ice supersaturations as in the observations. 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