A network of water vapor Raman lidars for improving heavy precipitation forecasting in southern France: introducing the WaLiNeAs initiative and first highlights from the 2022 field campaign

Abstract

Extreme heavy precipitation events (HPEs) pose a threat to human life but, despite regular improvement, remain difficult to predict because of the lack of adequate high frequency and high-resolution water vapor (WV) observations in the low troposphere (below 3 km). To fill this observational gap, The Water vapor Lidar Network Assimilation (WaLiNeAs) initiative aims at implementing an integrated prediction tool (IPT), coupling network measurements of WV profiles, and a numerical weather prediction system to try to improve the  forecasts of  the amount, timing, and location of rainfall associated with HPEs in southern France (struck by ~ 7 HPEs per year on average during the fall).In the fall/winter of 2022-2023, a network of 6 mobile Raman WV lidars was specifically implemented in Southern France (Aude, Gard, Var and Bouche du Rhone) and in Corsica. The network was complemented by 2 fixed Raman WV lidars in Barcelona and Valencia with the aim to provide measurements with high vertical resolution and accuracy to be assimilated in the French Application of Research to Operations at Mesoscale (AROME-France) model, using a four-dimensional ensemble-variational approach with 15-min updates in addition to the observations operationally assimilated (radar, satellites, …). This innovative IPT is expected to enhance the model capability for kilometer-scale prediction of HPEs over southern France up to 48 h in advance.The field campaign was conducted from October of 2022 to January 2023, to cover the period most propitious to heavy precipitation events in southern France. A consortium of French, German, Italian, and Spanish research groups operated the Raman WV lidar networkIn this presentation, we will provide an overview of the precipitation events in southern France during the WaLiNeAs campaign, as well as an outline of the operations period of the different Raman WV lidars and the lidar data monitoring procedure implemented during the experiment. We will highlight the cases of interest and provide an outlook at next steps towards lidar data assimilation in AROME.