Phys.org July 25, 2024
A team of researchers in the US (NSF National Center for Atmospheric Research, industry) provided substantial evidence for significant impacts of turbulence on the evolution of cloud droplet size distributions and rain formation by comparing high-resolution observations of cumulus congestus clouds with state-of-the-art large-eddy simulations coupled with a Lagrangian particle-based microphysics scheme. Turbulence causes earlier rain formation and greater rain accumulation compared to simulations with gravitational coalescence only. The observed rain size distribution tail just above cloud base follows a power law scaling that deviates from theoretical scalings considering either a purely gravitation collision kernel or a turbulent kernel neglecting droplet inertial effects. Large aerosols acting as cloud condensation nuclei (“giant CCN”) do not significantly impact rain formation because of their long timescale to reach equilibrium. According to the researchers turbulent coalescence must be included in the model to accurately represent the observed drop size distributions… read more. TECHNICAL ARTICLE
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