The effects of aerosol particles and clouds on atmospheric dynamics, weather, climate, and public health are among the central topics in current environmental research. Aerosol particles and clouds influence the Earth's radiative energy budget by scattering, absorption and emission of solar and terrestrial radiation. Furthermore, they play key roles in the hydrological cycle and in the formation of precipitation. Moreover, aerosol, cloud and precipitation particles affect the abundance of trace gases via heterogeneous chemical reactions and other multiphase processes. Aerosol effects on the formation of clouds and precipitation can lead to profound modifications in the dynamics and radiative properties of convective cloud systems. These processes may influence the vigor and organization of heavy weather events like hail and rainstorms and cascade all the way to changing the global circulation of the atmosphere and the Earth's energy budget The quantitative understanding and predictability of aerosol, cloud, and precipitation properties, interactions, and effects in the climate system are, however, very limited. The lack of simultaneous in-situ measurements of cloud microphysical properties, chemical tracer compounds and aerosol characteristics within deep convective clouds has been a serious obstacle to evaluate detailed cloud-resolving models that can be used for obtaining a more comprehensive understanding of aerosol-cloud interaction and convective tracer transport. The major bottleneck has been the difficulty to investigate and characterize these properties and interactions by in-situ and remote sensing observations. This applies especially to the regime where aerosol-cloud-precipitation interactions play a particularly important role, i.e., the challenging environment of deep convective clouds, from the cloud base through the mixed phase levels all the way up to the anvils. The complex interaction between cloud and aerosol strongly depends on the thermodynamics. The results for two distinct months of the most electrically active pre-monsoon regime, one dominated by boundary layer smoke and another with low CCN concentration, casts doubt on a primary role for the aerosol in enhancing the electrification. Recent results also show that the aerosol-cloud interaction strongly depends of the atmosphere instability; during highly unstable atmospheric conditions black carbon enhances precipitation formation and contrarily, during stable days, precipitation is reduced as black carbon concentration. Aerosol cloud interaction can potentially modify cloud microphysical properties and consequently the rainfall, cloud life cycle and lightning activity. The improvement in knowledge of this interaction can be used to validate and improve high resolution model and climate change simulations. The ACRIDICON-CHUVA is aiming at the elucidation and quantification of aerosol-cloud-precipitation interactions and their thermodynamic, dynamic and radiative effects in convective cloud systems by in-situ aircraft observations combined with indirect measurements (aircraft, satellite, and ground based (X Band dual Pol radar) and numerical simulations.

General scientific questions:

• Does the interaction of natural and anthropogenic aerosols with clouds and precipitation significantly influence the cloud microphysics, the formation, evolution and dynamics of convective cloud systems and the vigor of heavy weather events (hail and rainstorms)?
• Can these effects induce substantial changes in the global circulation of the atmosphere, the Earth's energy budget, and climate?
• What are the characteristic physical and chemical properties of aerosol and cloud particles in convective cloud systems (inflow, in-cloud, outflow), and how do they change in the course of cloud evolution?
• What are the effects of convective cloud systems on the solar and terrestrial radiation budget, and how can the three-dimensional microphysical structure of convective clouds be considered?
• Are the cloud processes over forest and deforested regions statistically different?