Fog

A ‘fogbow’, photographed in the Waipa District by Peter Urich.

Fog, and mist, are created by microscopic water droplets suspended in the air. These tiny water droplets scatter any light that passes through or past them, meaning that objects in the fog become hard to see. Fog and mist are then defined by how much the visibility is reduced. The International Civil Aviation Organisation definitions for fog and mist are:

Fog: a suspension of very small water droplets in air, reducing the visibility to 1000 metres or less.

Mist: similar to fog, however visibility will be reduced to no less than 1000 metres.

Haze is another phenomenon that can reduce visibility. However, this is a reduction in visibility caused by microscopic particles in the air, rather than by water droplets. For example, in New Zealand we sometimes get haze around our coastlines after we have had strong winds, as the wind can whip up sea spray and cause small particles of sea salt to be suspended in the air.