Two new multirotor UAVs for glaciogenic cloud seeding and aerosol measurements within the CLOUDLAB project

Abstract

Abstract. Uncrewed Aerial Vehicles (UAVs) have become widely used in a range of atmospheric science research applications. Because of their small size, flexible range of motion, adaptability, and low cost, multirotor UAVs are especially well-suited for probing the lower atmosphere. However, their use so far has been limited to conditions outside of clouds, first because of the difficulty of flying beyond visual line of sight, and second because of the challenge of flying in icing conditions in supercooled clouds. Here, we present two UAVs for cloud microphysical research: one UAV (the measurement UAV) equipped with a Portable Optical Particle Spectrometer (POPS) and meteorological sensors to probe the aerosol and meteorological properties in the boundary layer, and one UAV (the seeding UAV) equipped with seeding flares to produce a plume of particles that can initiate ice in supercooled clouds. A propeller heating mechanism on both UAVs allows for operating in supercooled clouds with icing conditions. These UAVs are an integral part of the CLOUDLAB project in which glaciogenic cloud seeding of supercooled low stratus clouds is utilized for studying aerosol-cloud interactions and ice crystal formation and growth. In this paper, we first show validations of the POPS onboard the measurement UAV, demonstrating that the rotor turbulence has a negligible effect on aerosol measurements. We exemplify its applicability for profiling the planetary boundary layer, as well as for sampling and characterizing aerosol plumes, in this case, the seeding plume. We explain the different flight patterns that are possible for both UAVs, namely horizontal or vertical leg patterns or hovering, with an extensive and flexible parameter space for designing the flight patterns according to our scientific goals. Finally, we show two examples of seeding experiments: first characterizing an out-of-cloud seeding plume with the measurement UAV flying horizontal transects through the plume, and second, characterizing an in-cloud seeding plume with downstream measurements with POPS on a tethered balloon. Particle concentrations and size distributions of the seeding plume from the experiments reveal that we can successfully produce and measure the seeding plume, both in-cloud and out-of-cloud. The methods presented here will be useful for probing the lower atmosphere, for characterizing aerosol plumes, and for deepening our cloud microphysical understanding through cloud seeding experiments, all of which have the potential to benefit the atmospheric science community.

Evaluating the Wegener-Bergeron-Findeisen process in ICON in large-eddy mode with in situ observations from the CLOUDLAB project

“…Unfortunately, the model overestimated the temperatures for 25 January 2023 (Henneberger et al, 2023) (Fig. 3a), while the temperatures on the 26 January 2023 were simulated adequately (Fig.…”

“…Both January days were characterized by low stratus clouds and low temperatures, which are the targeted conditions for conducting seeding experiments in this project. Here, we only briefly discuss the relevant instrumentation, and a full description of the experimental approach and instrumentation can be found in Henneberger et al (2023).…”

“…In this study, we evaluate the impact of cloud seeding in a numerical weather model (ICON, Zängl et al (2015)) by utilizing seeding experiments conducted within the CLOUDLAB project. CLOUDLAB aims to improve our understanding of ice crystal formation and growth by exploiting the methodology of glaciogenic cloud seeding in dynamically stable clouds (Henneberger et al, 2023). Persistent low stratus clouds proved to be a good natural laboratory given their persistent and frequent occurrence over Switzerland during wintertime.…”

“…To conduct the seeding experiments, an uncrewed aerial vehicle (UAV) is flown into the cloud to release seeding particles (AgI) upstream of the field site. The particles are then advected downstream to the field site by the wind, where the seeding-induced microphysical changes (i.e., formation and growth of ice crystals) are observed by an extensive remote sensing setup together with in situ instrumentation at high spatio-temporal resolution (Henneberger et al, 2023;Miller et al, 2023). This approach allows for repeated and laboratory-like experiments in quick succession, offering the ideal opportunity to evaluate microphysical schemes in models.…”