There Is A Mountain In Front Of Me!

23 October 2013

Merlion Wayfarer's recent posting on mushrooms and flying saucers in the sky ("The Mushroom That Became A Flying Saucer At Sunset") created so much excitement among her friends that she decided to investigate the rare occurrence of these clouds...

Mushrooms & Flying Saucers

Lenticular clouds (Altocumulus lenticularis) are stationary lens-shaped clouds with a smooth layered appearance that form in the troposphere, normally in perpendicular alignment to the wind direction. Lenticular clouds can be separated into altocumulus standing lenticularis (ACSL), stratocumulus standing lenticular (SCSL), and cirrocumulus standing lenticular (CCSL). Due to their shape, they have been offered as an explanation for some Unidentified Flying Object (UFO) sightings.

Where stable moist air flows over a mountain or a range of mountains, a series of large-scale standing waves may form on the downwind side. If the temperature at the crest of the wave drops to the dew point, moisture in the air may condense to form lenticular clouds. As the moist air moves back down into the trough of the wave, the cloud may evaporate back into vapor. Under certain conditions, long strings of lenticular clouds can form near the crest of each successive wave, creating a formation known as a "wave cloud." The wave systems cause large vertical air movements and so enough water vapor may condense to produce precipitation. The clouds have been mistaken for UFOs (or "visual cover" for UFOs) because these clouds have a characteristic lens appearance and a smooth saucer-like shape.

Lenticularis often shows iridescence if it is near or in front of the sun. Bright colors (called irisation) are sometimes seen along the edge of lenticular clouds...

Lenticular clouds are usually spotted among mountain ranges...

(Source : Wikipedia)

There are some cases where these clouds have also been known to form where a mountain does not exist, but rather as the result of shear winds created by a front.

(Source : WordPress)

In this case, the front was created by a thick dense "mountain" of cumulus clouds amid a sky filled with higher-level alto and strato clouds...

The rare Flying Saucer in Singapore...

The Cloud Cap

Cap cloud or cloud cap is a stratiform, orographic cloud that hovers above or over an isolated mountain peak, formed by the cooling and condensation of moist air forced up and over the peak and lenticularly shaped by horizontal upper level winds. The cloud appears to remain essentially stationary.

The term is also occasionally used for Pileus (Latin for cap) cloud. Unlike the mountain cap cloud, the pileus is essentially an accessory cloud, that appears as a smooth cap, or hood above a cumulus or cumulonimbus cloud. The cap forms when a humid layer is lifted to its dew point above a rising thermal. This may later penetrate the pileus, which will eventually be absorbed into the main cloud body. Sometimes several layers of pileus form above one another.

The Shadow

A cloud shadow occurring at sunset is formed when light is cast from a low level cloud onto a higher level cloud. During a sunset, the sun's rays will sometimes be blocked by a cumulus cloud below the horizon. Like any shadow, a darkened area will form. These types of cloud shadows are especially dramatic and can appear as darkened rays of light, sometimes referred to as crepuscular rays, as they appear in the same direction as the setting sun.

More photos are available on Merlion Wayfarer Goes Green's Picasa at :
Natural Phenomena - Clouds