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Supercooled water, still in liquid state Start of solidification as a result of leaving the state of rest. Supercooling, [1] also known as undercooling, [2] [3] is the process of lowering the temperature of a liquid below its freezing point without it becoming a solid.
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.
The freezing speed directly influences the nucleation process and ice crystal size. A supercooled liquid will stay in a liquid state below the normal freezing point when it has little opportunity for nucleation—that is, if it is pure enough and is in a smooth-enough container. Once agitated it will rapidly become a solid.
The melting point of water at 1 atmosphere of pressure is very close to 0 °C (32 °F; 273 K), and in the presence of nucleating substances the freezing point of water is close to the melting point, but in the absence of nucleators water can supercool to −40 °C (−40 °F; 233 K) before freezing.
Frazil ice forms in supercooled water which occurs because the surface water loses heat to cooler air above. Suppression is the idea of insulating the surface water with an intact, stable ice cover. The ice cover will prevent heat loss and warm the supercooled water that might have already formed. [11]
Under some atmospheric conditions, snow crystals may encounter supercooled water droplets. These droplets, which have a diameter of about 10 μm (0.00039 in) on average, can exist in the liquid state at temperatures as low as −40 °C (−40 °F), far below the normal freezing point as long as it is above the homogeneous nucleation point of ...
Circular or elliptical gap that can form in cirrocumulus or altocumulus clouds, caused by supercooled water evaporating or freezing, sometimes triggered by aircraft. These rare, striking holes ...
This process only happens at temperatures between 0 °C (32 °F) and −40 °C (−40 °F). Below −40 °C (−40 °F), liquid water will spontaneously nucleate, and freeze. The surface tension of the water allows the droplet to stay liquid well below its normal freezing point. When this happens, it is now supercooled liquid water.