Raman lidar measurements for the characterization of aerosol and cloud microphysical properties

A UV Raman lidar system (BASIL) is operational at DIFA-Univ. of Basilicata (Potenza-Italy). The major feature of BASIL is its capability to perform high-resolution and accurate measurements of atmospheric temperature, both in daytime and night-time, based on the application of the rotational Raman lidar technique in the UV. Besides temperature, BASIL is capable to provide measurements of particle backscatter at 355 and 532 nm, particle extinction at 355 nm, particle depolarization at 355 and water vapour mixing ratio. Relative humidity measurements are obtained from simultaneous water vapour mixing ratio and temperature measurements. Relative humidity is a key atmospheric parameter which controls cloud formation and aerosol optical properties. Accurate relative humidity measurements are fundamental to characterize cloud and aerosol radiative properties and related microphysical processes. Relative humidity measurements are also a precious tool to study upper tropospheric humidification due to cirrus sublimation, and to investigate the convective boundary layer and the passage of fronts. Specific case studies are considered and discussed to assess RH lidar measurement capability in presence of aerosols and clouds. Measurements of aerosol backscatter as a function of relative humidity are reported and discussed, highlighting the swelling tendency of hygroscopic aerosol for large relative humidity values.