Atmospheric precipitation

Condensed water falling from clouds or deposited from the atmosphere as liquid or solid particles. It can efficiently scavenge soluble gases and aerosol particles. Gas conversion into sulfate and subsequent atmospheric precipitation removal are separate stages of an atmospheric sulfur budget.

Liquid-water precipitation reaching the surface. In a catchment water balance its rate is an input measured as water depth per time; only the part not absorbed or otherwise lost becomes rainfall excess feeding overland flow.

Nucleation creates the initial ice embryo, either within liquid or with assistance from a suitable interface. Deposition, riming and ice-crystal aggregation enlarge already existing ice. A list of efficient ice-growth processes does not by itself explain how the first crystals formed. Small-particle nucleation probabilities depend on thermodynamic driving, interfaces, volume and exposure time.

Ice particles collide and stick to form a larger aggregate, such as a snowflake. Temperature, habit and collision speed affect sticking. This differs from vapour deposition onto ice and from riming, in which collected supercooled liquid freezes on the ice particle. ^[ref]

The fraction of a specified condensate or moisture supply that appears as precipitation under a stated spatial, temporal and flux convention. Collection, fall-out, entrainment, evaporation and sublimation all affect it. A cloud can activate many droplets yet precipitate inefficiently; droplet formation, growth to precipitation size and survival to the surface are separate requirements.

Supercooled droplets collide with an ice particle and freeze onto it, increasing its mass. Deposition, riming and ice aggregation are distinct growth mechanisms.

Because ice has lower equilibrium vapour pressure than supercooled liquid, a mixed-phase environment can sustain deposition onto ice while liquid droplets evaporate. This is distinct from ice collecting droplets by riming.