A new methodology for the statistical descriptions of Particle‐by‐Particle measurements of liquid droplets in cumulus clouds

Abstract

AbstractStatistical and microphysical properties of liquid cloud droplets (with diameter 2–50 μm) in the growing stage of cumulus clouds are illustrated by in situ Particle‐by‐Particle (PbP) measurements. A contrasting statistical behaviour for the cloud core, following Poisson statistics with an indication of random spatial distribution, and the cloud edge which unveils non‐Poisson statistics, tells of a heterogeneous spatial distribution. A new metric from the joint probability distribution function of droplet inter‐arrival distance and droplet size is proposed for quantifying the dynamics–microphysics interaction in cumulus clouds. We found that the interaction is stronger for the cloud edge compared to the undiluted core region. The scale dependency of mixing is studied using PbP data, and reveals a sharp change at length‐scales below a critical value of around 40–60 cm, above which microphysical change of mixing is almost constant. This critical length‐scale separates the mixing regimes between the homogeneous and inhomogeneous processes. Observation of such a critical length‐scale of mixing from in situ measurements (at sub‐metre scale) is the key finding of this study.