Mammatus (also known as mamma or mammatocumulus) is a meteorological term applied to a cellular pattern of pouches hanging underneath the base of a cloud. These pouches, typically measuring about half a kilometer in diameter, are often ragged, but may appear smooth. Their color is normally a bluish gray, the same as that of the host cloud, but direct illumination from the setting sun and other clouds may cause a gold or reddish cast. Mammatus can persist anywhere from minutes to hours, diffusing and disappearing over time.
The mechanism of their production is poorly understood and has been little studied. The presence of very dry air beneath the cloud base is known to be a factor.
I swear I’ve never heard of mammatus clouds before today. I’m still stuck in cirrocumulus world, I suppose.
Tons of Mammatus cloud photos here.
(via ponzu)
