Study of a heavy precipitation event over southern France, in the frame of HYMEX project: Observational analysis and model results using assimilation of lightning

摘要

Here, a heavy precipitation event that affected Southern France in the period of 6-8 September 2010 is studied. This event produced more than 300 mm in a 24-h period and resulted in floods in an area that has been often affected by similar events during autumn. The system has been monitored by in situ surface stations, radar, lightning networks and satellites that put into evidence the anchoring of convective cells along mountainous areas. The precipitation episode was simulated using the MM5 non-hydrostatic model at very high resolution. Moreover, an assimilation technique has been applied that controls the activation of the convective parameterisation scheme using lightning data as a proxy for the presence of convection. The assimilation of lightning proved to have a positive impact on the representation of the precipitation field, providing also more realistic positioning of the precipitation maxima, mainly during the second day of the event. The improvement of the model simulation when lightning was assimilated was quantitatively supported by the verification against observations. The improvement of monitoring, understanding and forecasting of such type of events is in line with the scientific topics prescribed within HYMEX international project.