Study of a Mesoscale Convective System Using a Raman Lidar inthe Frame of the Convective and Orographically-InducedPrecipitation Study

On 20 July 2007, a vorticity maximum at the east side of a jet initiated over middle - eastern France triggered cyclogenesis and a Mesoscale System (MCS) passed over the Convective and Orographically-induced Precipitation Study (COPS) region. The University of BASILicata Raman lidar system (BASIL) was deployed in Rhine valley at Achern, (Supersite R, Lat: 48.64°N, Long: 8.060E, Elev.: 140 m) in the frame of the COPS. BASIL was operated continuously during this day, providing measurements of aerosols, temperature and water vapour. The approaching thunderstorm modified the pre-storm environment and determined a lowering of the anvil clouds, which is visible in the lidar data, to changing the state of the layer. In particular, a mid-level outflow region was present, with hydrometeor-debris leaving the main thunderstorm core and being recycled back into it (mostly in the form of virga). The MCS modified the pre-storm environment at 1.6-2.5 km directly (outflow) and at lower levels through precipitation (in the form of virga). Wave structures were also evident in the particle backscatter data, a result of the shear produced by the outflow and inflow winds. There was also increase in moisture ahead of the cold front and decrease as the cold front passed by, explained as a combination of the “moisture pooling” before the front and subsequent cold air displacement. This MCS generation and cold front passage was associated with a temperature decrease of about 4.5 K. Data collected on this day demonstrate the utility of Raman lidar systems as BASIL in visualizing multi-scale interactions that occurred during the MCS and its effects in terms of modification of the pre-storm environment.