Thursday, November 12, 2009

Mammatus Clouds

One week into October a line of thunderstorms formed in the Del Norte Mountains of the Trans-Pecos. Dark anvil shaped thunderheads obscured the tops of Mount Ord and Cathedral Mountain. The slanted penetrating rain sheets could be seen from the town below and then as the late evening sun broke though the thinner clouds in the west a blanket of strange sagging gray puffs of laden visible moisture reflected oddly in the dying light and descended into the town’s valley as if a symbol of some new world chaos.

Mammatus or Mammatocumulus clouds are a rare pouch-like cloud structures that form in sinking air usually in the aftermath or on the underside of a thunderstorm where distinct temperature gradients, moisture and wind shear are present and most often when cumulonimbus anvil clouds have formed. The name is derived from the Latin word Mamma meaning udder or breast as some believe these clouds resemble a woman’s breast.

The opaque and lumpy lobes cluster and can cover the sky for miles and each lobe last an average of ten minutes before evaporation dissolves them. They are usually composed of ice crystals or a combination of ice and water.

Inside the cumulonimbus storm clouds, updrafts carry heavy wet air to the top until the momentum is lost and this subsiding air spreads horizontally and accumulates at the base of the cloud. Sagging with water or ice these air-suspended bosoms dangle and cluster in the sky and occasionally form the rare Mammatus cloud.

At least ten theories exist on exactly how they form but because of their rarity and chance sightings observational information remains thin. Much knowledge on micro-physical cloud processes lie on the unknown outside edge of the scientific frontier.

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