![]() Precipitation is a transient state, but though its effects are largely indirect, they have immense consequences for planetary climate. Because precipitating particles can fall far from the air mass where they form, they redistribute both heat and the condensible species within an atmosphere. ![]() ![]() Extensive vertical displacement relative to the local air mass distinguishes precipitation from clouds. Within a planetary condensible cycle, precipitation is the transport of the condensible species in a condensed phase (liquid or solid) through the atmosphere and, for terrestrial planets, to the surface. 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. 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. 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. 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. ![]() 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. ![]()
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