UAV-Based Insights into Cloud Particle Size Distributions from the CHOPIN Campaign

Clouds play an important role in the Earth’s climate through well-established mechanisms, such as their interactions with solar radiation and their role in precipitation. However, their influence on future climate projections remains highly uncertain. One of the key challenges is the understanding of aerosol-cloud interactions in studying clouds, as aerosols can serve as cloud condensation nuclei.  Aerosols can have significant variability across both space and time. While in situ measurements provide precise data for a small atmospheric volume—just a few cubic centimetres—they may not accurately reflect the spatial (horizontal and vertical) variability of aerosol characteristics and therefore do not give accurate statistical information on the average cloud state and its variability.

Airborne observations offer the capability of sampling a larger volume of the atmosphere and therefore give a more comprehensive understanding of clouds.This study highlights UAV-based observations of particle size distributions both inside and outside clouds, conducted during the #CHOPIN (CleanCloud Helmos Orographic Site Experiment) campaign. As part of this campaign, the Unmanned Systems Research Laboratory (USRL) of the Cyprus Institute deployed light Unmanned Aircraft Systems at Mt. Helmos, Greece, from October 11 to November 1, 2024, providing valuable data for the study of clouds and their interactions with aerosols. This is one of the few times USRL/CYI reported observations aerosol-cloud interaction flights.

The #CHOPIN campaign, conducted in collaboration with NCSR Demokritos and FORTH/EPFL, was hosted at the Kalavryta Ski Center with a base altitude for the UAS takeoffs and landings of ~1.7 km ASL. The campaign aimed to improve the understanding of aerosol-cloud interactions and to evaluate remote sensing algorithms and models. Located in a rapidly changing "climate hotspot" at the intersection of various air masses, Mount Helmos is particularly sensitive to environmental changes, with interactions between wildfire smoke, pollution, sea salt, and Saharan dust. This unique setting provides an ideal location to study the dynamics of aerosol-cloud interactions.

During the campaign, several flights were performed inside and outside clouds operating in a horizontal area of approximately ~16km² and providing vertical profiles of particle size distribution from the ground up to 3.5 km ASL. We will focus on the cloud observations and the derivation of particle and droplet size distributions from UAV-based optical particle counters. These observations provide a good dataset for improving cloud-resolving models and for comparison with fixed station observations.