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Quarterly Journal of the Royal Meteorological Society 138, 667 (2012) 1652-1667
Assimilation of water-vapour airborne lidar observations: impact study on the COPS precipitation forecasts
S. Bielli 1, M. Grzeschik 1, Evelyne Richard 1, Cyrille Flamant 2, 3, 4, Cedric Champollion 5, C. Kiemle 6, M. Dorninger 7, P. Brousseau 8
(2012)

The Convective and Orographically-driven Precipitation Study (COPS) carried out in summer 2007 over northeastern France and southwestern Germany provided a fairly comprehensive description of the low-troposphere water-vapour field, thanks in particular to the deployment of two airborne differential absorption lidar systems. These lidar observations were assimilated using the 3D-Var assimilation system of the Application of Research to Operations at MEsoscale (AROME) numerical weather prediction mesoscale model. The assimilation was carried out for the period 4 July-3 August by running a three-hour forward intermittent assimilation cycle. First, the impact of the lidar observations was assessed by comparing the analyses with a set of more than 200 independent soundings. The lidar observations were found to have a positive impact on the analyses by reducing the dry bias in the first 500 m above ground level and by diminishing the root-mean-square error by roughly 15% in the first km. Then the impact of the lidar observations was assessed by comparing the precipitation forecasts (obtained with and without the lidar observations for the period 15 July-2 August) with the gridded precipitation observations provided by the Vienna Enhanced Resolution Analysis. In general, the impact was found to be positive but not significant for the 24 h precipitation and positive and significant for the 6 h precipitation, with an improvement lasting up to 24 h. Some selected case studies show that the improvement was obtained through a better depiction of convection initiation or through a more accurate positioning of the precipitation systems
1 :  Laboratoire d'aérologie (LA)
CNRS : UMR5560 – Observatoire Midi-Pyrénées – INSU – Université Paul Sabatier (UPS) - Toulouse III
2 :  Institut Pierre-Simon-Laplace (IPSL)
CNRS : FR636 – Institut de recherche pour le développement [IRD] – CEA – CNES – INSU – Université Pierre et Marie Curie (UPMC) - Paris VI – Université de Versailles Saint-Quentin-en-Yvelines (UVSQ) – École normale supérieure [ENS] - Paris
3 :  Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS)
CNRS : UMR8190 – Université Pierre et Marie Curie (UPMC) - Paris VI – Université de Versailles Saint-Quentin-en-Yvelines (UVSQ) – INSU
4 :  Université Pierre et Marie Curie - Paris 6 (UPMC)
Université Pierre et Marie Curie (UPMC) - Paris VI
5 :  Géosciences Montpellier (GM)
CNRS : UMR5243 – Université Montpellier II - Sciences et techniques
6 :  Deutsches Zentrum für Luft- und Raumfahrt (DLR)
Deutsches Zentrum für Luft- und Raumfahrt (DLR)
7 :  Department of Meteorology and Geophysics, University of Vienna
University of Vienna
8 :  Groupe d'étude de l'atmosphère météorologique (CNRM-GAME)
CNRS : URA1357 – INSU – Météo France
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Planète et Univers/Sciences de la Terre/Météorologie
LEANDRE 2 – WALES – AROME – VERA