Unifying Observations, Simulations, and Theory for Drizzle Size Distribution Tails

The onset and rate of drizzle remain open problems in atmospheric physics. This study brings together theory, simulations, and observations to analyze the emergence of power-law tails in droplet size distributions as a signature of a dynamic steady state with coalescence growth balanced by sedimentation removal. By applying a collector-mode approximation, analytic solutions are derived, predicting a droplet radius distribution scaling of (Formula presented.), assuming a collection kernel (Formula presented.). These predictions are validated against large eddy simulations of stratocumulus clouds, which exhibit the expected (Formula presented.) scaling in the drizzle tail. Furthermore, in situ measurements from stratocumulus clouds sampled during the ACE-ENA campaign demonstrate robust power-law behavior in the 30–100 μm range, yielding a power-law exponent of 4.09. The time to reach this steady state is determined by the growth rate at the minimum size droplets experiencing coalescence.