fog

A hydrometeor consisting of the suspension of small-diameter, usually microscopic water droplets, which reduce horizontal visibility at the Earth's surface level to below one kilometer. That maximum viewing distance marks the boundary between fog (niebla) and mist (neblina). Outside the meteorological context, the term is also used to refer to, for example, the signal received by a television set when no channel is tuned in, to the blurred vision caused by dust getting into one of our eyes, or as a synonym for mystery or uncertainty. Returning to the meteorological phenomenon itself, fog is, in most cases, a cloud of the genus Stratus, whose base coincides with the Earth's surface, and it can arise both over the sea and over dry land. Fogs can be classified according to different criteria. If the formation mechanism is what is taken into account, three main types can be considered: 1) advection; 2) evaporation; and 3) radiation (or irradiation). Within each of these categories, specific types of fog are in turn included, as detailed in the following entries.