Convective Ripening and Initiation of Rainfall

TL;DR

This paper introduces 'convective ripening', a non-collisional process that accelerates droplet growth in clouds, providing a faster explanation for rainfall initiation from small water droplets without relying on collisions.

Contribution

The paper proposes a novel non-collisional model called 'convective ripening' for droplet size broadening and explains its role in rapid rainfall initiation from ice-free clouds.

Findings

Convective ripening accelerates droplet growth compared to collisional mechanisms.

Non-collisional process explains rain formation from small droplets within realistic cloud conditions.

Collisional mechanisms are insufficient for rain initiation from 20 μm droplets.

Abstract

This paper discusses the evolution of the droplet size distribution for a liquid-in-gas aerosol contained in a Rayleigh-B\'enard cell. It introduces a non-collisional model for broadening the droplet size distribution, termed 'convective ripening'. The paper also considers the initiation of rainfall from ice-free cumulus clouds. It is argued that while collisional mechanisms cannot explain the production of rain from clouds with water droplet diameters of $20\ \mu {\rm m}$, the non-collisional convective ripening mechanism gives a much faster route to increasing the size of the small fraction of droplets that grow into raindrops.