Retrieving Microphysical Properties of Arctic and Mediterranean clouds using a synergy of remote sensing and in situ instrumentation

Aerosol-Cloud Interactions (ACI) play an important role in the hydrological cycle and are strong modulators of cloud radiative forcing and climate. Nevertheless, they remain poorly understood and constrained despite decades of research, because many processes and feedbacks are highly uncertain and are challenging to describe in regional and global climate models. Even less understood is the role of natural aerosol and ACI in a post-fossil future, where anthropogenic emissions is vastly reduced but emerging “natural” aerosol sources modulated by anthropogenic climate change (biomass burning, bioaerosols, dust) will dominate. The CleanCloud project aims to address these uncertainties and as part of its activities carries out major observational field campaigns at climate hot spots (Arctic, Mediterranean) to better constrain ACI processes, and, evaluate, improve and develop new remote sensing algorithms for studying aerosols, clouds and ACI.

The first CleanCloud campaign was based at the Villum Research Station (81.6° N, 16.6° W) in North Greenland, with in-situ and remote sensing measurements, and consisted of two phases, one during the spring (16 March – 13 April) and one during summer (16 July – 13 August) of 2024, in collaboration with the NASA ARCSIX aircraft mission. The second campaign, named “Cleancloud Helmos OrograPhic site experimeNt (CHOPIN)”, is ongoing and is anticipated to last for 6 months, starting from 1 October at Mt.Helmos (38.0^o N, 22.2^o E) in the Peloponnese, Greece. A series of in situ and remote sensing measurements were distributed at 6 sites along the lee side of Mt. Helmos, 4 at the Kalavrita ski Center’s parking lot (altitude ~ 1690 m), 1 at the foothills (altitude ~ 1747 m) and the Helmos Hellenic Atmospheric Aerosol and Climate Change station ((HAC)²) at the mountaintop (altitude ~ 2314 m) constrain almost every aspect of the aerosols, clouds and their interaction in the region – and especially in the orographic clouds that form at the (HAC)² station.

Here, we present results from these two campaigns to examine the cloud (e.g., droplet number concentration & size) and aerosol microphysical characteristics (size distribution, CCN concentrations, chemical composition, bioaerosol number concentration and type) and cloud-scale dynamical forcing (vertical velocity) to understand their contribution to ACI processes. Radiosondes to derive the vertical structure of the atmosphere, Lidar systems and sun photometers were used to determine the presence of aerosol amount, their altitude and type (bioaerosol, dust, pollution, biomass burning) as well as the aerosol optical and columnar microphysical properties, Doppler lidars for turbulence and cloud-scale dynamics, radars to obtain the microphysical properties of the clouds, and finally satellites to retrieve the spatio-temporal evolution of the clouds. Additionally, in the case of CHOPIN campaign, cloud probes and cloud samplers were used to perform in-cloud sampling and to obtain the cloud microphysical properties. Thus, the use of this synergistic approach enables us to perform closure studies and to improve our current retrievals to predict cloud properties. These extensive field campaigns will aid in developing new ACI-related retrieval algorithms, development/improvement of parameterizations, and the ESA EarthCARE calibration/validation activities.