Fog Seeding/Fog Dissipation
There are two primary fog types: warm and cold fog. These fog types are differentiated by temperature, with warm fog occurring at 32°F (0°C)or above, and cold fog at temperatures below 32°F (0°C). Both types are composed of water droplets. Warm fog is the more common of the two in most parts of the world, is microphysically stable and difficult to modify. Cold fog, on the other hand, is microphysically unstable and can be modified much more readily via fog seeding. Water droplets in these fogs can be frozen by the introduction of a heterogeneous seeding agent such as silver iodide or homogeneous agents such as dry ice (solid carbon dioxide) or liquefied propane.
These seeding techniques are commonly known as 'fog clearing' or 'fog dispersal'. Ground-based equipment can be used to dispense silver iodide or to vent liquefied propane. Aircraft can be used to drop small particles of dry ice into the fog. The typical application of this technology is to improve the visibility in the vicinity of airports.
North American Weather Consultants (NAWC) can acquire licenses to utilize University of Utah patent #5628455. An embodiment of the patented invention is a method for the reduction of supercooled fog, which comprises introducing liquid carbon dioxide into the fog from and along the ground by moving vehicles, in a quantity to diminish the supercooled fog. The method is of potential value in activities in which poor visibility due to the presence of supercooled fog is a constraining factor (e.g. winter airport operations).