Development of Biodegradable Helium Balloon for Atmospheric Mini Radio-Probes and Measurement of Physical Fluctuations within the Atmospheric Boundary Layer

Understanding turbulent processes in clouds is one of the most important challenges in atmospheric physics and one of the main sources of uncertainty in climate models. Clouds regulate the hydrological cycle and the Earth’s energy balance, but the mechanisms that control their dynamics are still only partly understood. The classical turbulence theory by Kolmogorov (K41), while fundamental, is based on three assumptions — stationarity, homogeneity, and isotropy — which are rarely satisfied in real atmospheric flows. Nu- merical simulations try to address these limits, but at the current state of the art they can only cover small portions of reality: DNS are restricted to domains of a few meters, while global models work with grids of several kilometers, which cannot describe local microphysical processes. Besides numerical models, experimental observations are also limited. Radars, aircraft, and large balloons provide useful data, but they cannot follow the evolution of flows at small scales. To really understand the dynamics of the Atmospheric Boundary Layer (ABL) and of clouds, a different approach is needed: one that looks at the atmosphere from the point of view of the air particles, in a Lagrangian way, able to capture the evolution and fluctuations of physical quantities down to the smallest scales. This is the challenge of the European COMPLETE project (Horizon 2020), which introduces ultralight and environmentally sustainable radiosondes, designed to follow the atmospheric flow like tracked particles. These sondes collect thermodynamic and kine- matic data in situ and send them in real time to ground receiving stations, and when launched in clusters they make it possible to build multipoint Lagrangian datasets. This thesis first describes the radiosondes developed in the COMPLETE project and the environment where they operate, with focus on atmospheric turbulence and cloud processes. Then, it presents two main personal contributions. The first is the design, construction, and testing of a double-wheel thermal sealer, developed to improve the re- liability and efficiency of the production of aerostatic balloons, essential for the flotation of the sondes on isopycnic surfaces. The second is the analysis of data from two experi- mental launches, with a single sonde and with a cluster respectively, used to test a new communication system based on a public network of ground stations worldwide, opening new perspectives for the future of the project.