Atmospheres & Climate

The Physics of Falling Raindrops in Diverse Planetary Atmospheres

By Keith Cowing
February 22, 2021
Filed under
The Physics of Falling Raindrops in Diverse Planetary Atmospheres

The evolution of a single raindrop falling below a cloud is governed by fluid dynamics and thermodynamics fundamentally transferable to planetary atmospheres beyond modern Earth’s.

Here, we show how three properties that characterize falling raindrops — raindrop shape, terminal velocity, and evaporation rate — can be calculated as a function of raindrop size in any planetary atmosphere. We demonstrate that these simple, interrelated characteristics tightly bound the possible size range of raindrops in a given atmosphere, independently of poorly understood growth mechanisms.

Starting from the equations governing raindrop falling and evaporation, we demonstrate that raindrop ability to vertically transport latent heat and condensible mass can be well captured by a new dimensionless number. Our results have implications for precipitation efficiency, convective storm dynamics, and rainfall rates, which are properties of interest for understanding planetary radiative balance and (in the case of terrestrial planets) rainfall-driven surface erosion.

Kaitlyn Loftus, Robin Wordsworth

Comments: submitted to JGR: Planets; 40 pages, 8 figures, 3 tables, 4 appendices; supporting information with 9 pages, 8 figures, 1 table; associated code at this https URL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Atmospheric and Oceanic Physics (
Cite as: arXiv:2102.09570 [astro-ph.EP] (or arXiv:2102.09570v1 [astro-ph.EP] for this version)
Submission history
From: Kaitlyn Loftus [view email]
[v1] Thu, 18 Feb 2021 19:00:01 UTC (2,127 KB)
Astrobiology, Astrochemistry,

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) πŸ––πŸ»