Sea of clouds
A sea of clouds is an overcast layer of clouds, viewed from above, with a relatively uniform top which shows undulations of very different lengths resembling waves. A sea of fog is formed from stratus clouds or fog and does not shows undulations.
In both cases, the phenomenon looks very similar to the open ocean. The comparison is even more complete if some mountain peaks raise above the clouds like some islands.
Formation
A sea of clouds forms generally in valleys or over seas in very stable air mass conditions such as in a temperature inversion. Humidity can then reach saturation and condensation leads to a very uniform stratocumulus cloud, stratus cloud or fog. Above this layer, the air must be dry. This is a common situation in a high pressure area with cooling at the surface by radiative cooling at night in summer, or advection of cold air in winter or in a marine layer.
Artistic uses
The term Sea of Clouds (雲海) is a Chinese poetic term for the surroundings of a mountain's summit, such as the one at Huangshan.
