At the EGU General Assembly 2025, held in Vienna from 27 April to 2 May, the Philofluid Research group presented exciting new developments in the study of turbulent dispersion within the atmospheric boundary layer (ABL). Through both a poster and an oral presentation, the team introduced innovative techniques and field results that deepen our understanding of relative dispersion under realistic atmospheric conditions.

The poster, titled “Innovative Lagrangian Radiosonde Clusters for ABL Observations”, showcased the design and deployment of miniaturized radiosonde clusters. These balloon-borne instruments (~40 cm in diameter) are capable of capturing Lagrangian trajectories in the turbulent ABL, providing high-resolution data for tracking inter-particle dispersion—something long theorized but rarely achieved with this level of detail.

In the accompanying oral presentation, “New ABL Measurements of Lagrangian Relative Dispersion by Means of Radiosonde Clusters”, the team reported findings from six radiosonde cluster launches across three topographically diverse regions: the maritime plains of Chilbolton (UK), the western Alps near the Aosta Valley Observatory (Italy), and the hilly landscapes surrounding Udine (Italy). The first operational prototype of the radiosonde cluster developed at POLITO was tested in several field campaigns from November 2022 to September 2024. These campaigns, which included six cluster launch experiments, were conducted in collaboration with CNR-INRIM, MET-OFFICE, NCAS, ARPA Piemonte, ARPA-FVG, and OAvdA.

The study centers on Lagrangian relative dispersion, a fundamental process in turbulence where particle pairs in a flow separate over time. Classical theories—most notably the Richardson-Obukhov (RO) law—predict that the mean square separation between particles scales with the cube of time. However, this assumes idealized homogeneous and isotropic turbulence, which the atmosphere rarely provides.

Field data presented by Philofluid revealed:

• Clear deviations from RO scaling, both between and within launches,

• Evidence of multiple dispersion regimes in individual events,

• Indications that site-specific boundary layer dynamics—such as intermittency, entrainment, and stratification—play a critical role in shaping dispersion behavior.

These findings reaffirm that real-world atmospheric turbulence cannot be captured by a universal scaling law. Instead, local flow structures and conditions must be understood in detail to interpret dispersion dynamics effectively.

Looking ahead, the group aims to identify which specific features of the ABL most strongly influence dispersion regimes—a formidable challenge given the variety of interacting turbulent processes involved.

This work represents a major step toward bridging the gap between classical turbulence theory and observational atmospheric science, and it opens the door to more refined, data-driven models for particle transport in the atmosphere.