Do all raindrops fall at terminal speed?

Abstract

A unique relation between raindrop size and fall speed v t ( D ) is assumed throughout atmospheric science. Yet, our speed versus size measurements of millions of drops during natural rainfall events show that many intermediate sized raindrops fall up to an order of magnitude faster than expected. Furthermore, images of drop clusters reveal that these “super‐terminal drops” are differently sized fragments of a recent break‐up, moving with the speed of the parent drop and relaxing towards v t ( D ). Additional evidence of the break‐up conjecture includes: (i) positive skewness in the distribution of fall speed deviations, (ii) strong size dependence of fall speed deviations and their maximum values and, (iii) preponderance of super‐terminal drops in the presence of large raindrops (i.e., during periods of high rainfall rates).