Mount Kinabalu Pileus

June 10, 2005


Provided by: Ivar Marthinusen
Summary authors & editors: Ivar Marthinusen ; Jim Foster

I was recently in Kota Kinabalu, Malaysia (island of Borneo) watching a huge cumulonimbus cloud rise fast above Mount Kinabalu (4,101 meters). After towering to what looked like twice the height of the mountain, a smooth, silkly cloud (pileus cloud) appeared just above one of the cumulonimbus turrets (shown above). It lasted for approximately two minutes and then disappeared, as the cumulonimbus cloud rose above it.

Pileus is Latin for "cap" or "skull cap." If the layer of air above a rising cumulus cloud is nearly saturated, the additional lift from below is occasionally sufficient to saturate it completely, forming a smooth and rounded cloud. Pileus clouds are occasionally seen just before a thunderstorm.

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