THE “A5-UNIBO” EXPERIMENT ON-BOARD BEXUS 18 STRATOSPHERIC BALLOON

Aerosols are able to affect climate in two major ways, namely direct and indirect process. The direct effect is the one exerted by aerosols themselves on the radiative balance of the Earth through a combination of scattering and absorption of radiation. The indirect effects are a suite of possible impacts on aerosols through the modification of cloud properties interaction of aerosols on clouds (IPCC, 2013). Clouds and aerosols still contribute the largest uncertainty to the correct assessment and understanding of “climate change” (IPCC, 2013). Ion-induced nucleation has been proposed to act in addition to the classical homogeneous nucleation (Iida et al., 2006; Hirsikko et al., 2007; Laakso et al., 2007). In particular, possible links between cloud formation processes and the ionization of atmospheric particles caused by Cosmic Rays have been proposed. The most widely studied mechanism proposed to explain the possible influence of the cosmic ray flux on cloudiness is the “ion aerosol clear air” mechanism (Carslaw et al., 2002; Usoskin and Kovaltsov, 2008). Our current understanding of these phenomena remains very low, mostly due to the reduced number of conclusive observations and our dependence on model simulations of these phenomena. The “A5-Unibo” experiment flown in BEXUS18 stratospheric balloon has been developed by the University of Bologna to this aim. The primary objective of the experiment was to collect vertical profiles of different atmospheric parameters involved in the above-mentioned processes, while the secondary one was the sampling of stratospheric aerosols for a post-flight analysis. In fact, A5-Unibo experiment measured profiles of particles size distribution with an innovative aerosol counter (LOAC “Light Optical Particle Counter”, MeteoMODEM,), positive and negative ion densities (Air Ion Counter, AlphaLab. Inc.), together with key atmospheric parameters (such as temperature, humidity, and pressure). In this way, a correlation between ionization and aerosol formation processes has been investigated through a rather simple multi-instrument approach. Our preliminary results have identified a possible role of positive ions in condensation, as well as a larger importance of humidity with respect to temperature.