Assimilation of water-vapour airborne lidar observations: impact study on the COPS precipitation forecasts

Abstract : 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
Keywords : LEANDRE 2 WALES AROME VERA
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Journal articles
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Submitted on : Thursday, January 12, 2012 - 9:41:13 PM
Last modification on : Monday, October 28, 2019 - 4:59:25 PM

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Soline Bielli, Matthias Grzeschik, Evelyne Richard, Cyrille Flamant, Cedric Champollion, et al.. Assimilation of water-vapour airborne lidar observations: impact study on the COPS precipitation forecasts. Quarterly Journal of the Royal Meteorological Society, Wiley, 2012, 138 (667), pp.1652-1667. ⟨10.1002/qj.1864⟩. ⟨hal-00659497⟩

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