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The Wegener–Bergeron–Findeisen process (after Alfred Wegener, Tor Bergeron and Walter Findeisen []), (or "cold-rain process") is a process of ice crystal growth that occurs in mixed phase clouds (containing a mixture of supercooled water and ice) in regions where the ambient vapor pressure falls between the saturation vapor pressure over water and the lower saturation vapor pressure over ice.
One example of deposition is the process by which, in sub-freezing air, water vapour changes directly to ice without first becoming a liquid. This is how frost and hoar frost form on the ground or other surfaces. Another example is when frost forms on a leaf. For deposition to occur, thermal energy must be removed from a gas.
Familiar examples are the melting of ice or the boiling of water (the water does not instantly turn into vapor, but forms a turbulent mixture of liquid water and vapor bubbles). Yoseph Imry and Michael Wortis showed that quenched disorder can broaden a first-order transition. That is, the transformation is completed over a finite range of ...
The corresponding depletion of water vapor causes the droplets to evaporate, meaning that the ice crystals grow at the droplets' expense. These large crystals are an efficient source of precipitation, since they fall through the atmosphere due to their mass, and may collide and stick together in clusters, or aggregates.
The symmetric shapes are due to depositional growth, which is when ice forms directly from water vapor in the atmosphere. [5] Small spaces in atmospheric particles can also collect water, freeze, and form ice crystals. [6] [7] This is known as nucleation. [8] Snowflakes form when additional vapor freezes onto an existing ice crystal. [9] [10]
Water vapor plays a role as it deposits ice crystals, known as hoar frost, during cold, still conditions. [54] During this transition, snow "is a highly porous, sintered material made up of a continuous ice structure and a continuously connected pore space, forming together the snow microstructure".
English: Phase diagram of water as a log-lin chart with pressure from 1 Pa to 1 TPa and temperature from 0 K to 650 K, compiled from data in and . Note that the phases of Ice X and XI (hexagonal) differ from the diagram in . Simplified version.
Water vapor can also be indirect evidence supporting the presence of extraterrestrial liquid water in the case of some planetary mass objects. Water vapor, which reacts to temperature changes, is referred to as a 'feedback', because it amplifies the effect of forces that initially cause the warming. Therefore, it is a greenhouse gas. [2]