Ground-based remote sensing observations of aerosols and clouds above a coastal site in the Central Mediterranean

Aerosol particles, acting as condensation nuclei, affect the cloud microphysical and radiative properties as well as the precipitation processes. Aerosol-cloud interactions are not well understood and quantified yet. With the aim to contribute to their understanding, quantify the role of dust and marine aerosol in the cold and warm cloud formation, and for testing model parameterization, the MESSA-DIN (MEditerranean Sea Salt And Dust Ice Nuclei) measurement campaign was organized and carried out by the CNR-IMAA Atmospheric Observatory (CIAO), part of the Italian component of the European research infrastructure ACTRIS (Aerosol Clouds Trace gases Research InfraStructure). The measurements were performed at the coastal site of Soverato (10 m asl, 38.69^◦ N, 16.54^◦ E), on the South-Eastern coast of Italy, in the Central Mediterranean, from June to November 2021. Different types of remote sensing instruments were deployed and operated at the measurement site, including a polarization Raman lidar, a ceilometer, a Doppler lidar, a cloud Doppler radar, a microwave radiometer, a sun photometer and a sky-imager.

The synergy processing of the measurements from part of these instruments, using the ACTRIS algorithms, allows to distinguish between the aerosol and the different types of hydrometeors forming clouds and precipitations, as well as to retrieve aerosol geometrical and optical properties together with cloud geometrical and microphysical properties through the troposphere. The profiles of aerosol optical properties may allow to identify aerosol types and to retrieve their concentration profiles, using or adapting existing algorithms such as POLIPHON (Polarization Lidar Photometer Networking). Aerosol-type specific concentration profiles are used in models’ aerosol-type specific parameterizations for estimating cloud-relevant aerosol microphysical parameters, which are the concentration profiles of cloud condensation nuclei (CCN) and ice nucleating particles (INP). The above information and retrievals are investigated in synergy with air masses vertical and horizontal velocities through the troposphere, estimated from the Doppler lidar, and with column-integrated aerosol optical and microphysical properties, retrieved by the sun photometer using the AERONET (Aerosol Robotic Network) algorithms.

Case studies related to the formation of warm and cold clouds in presence of dust, marine aerosol and their mixture are discussed. Moreover, for cold clouds, the observational products are compared with the results of a DREAM-based aerosol transport model with included parameterizations for INP originating from both dust and marine aerosols, developed by the Republic Hydrometeorological Service of Serbia. Finally, correlations between clouds formation and properties and aerosol type and properties are also investigated, considering the role of vertical and horizontal wind profiles and other thermodynamic variables derived from observations or models.