Jackiemu via Wikimedia Commons
Look at the picture to the left, and you may think it is fake, photoshopped, or perhaps even a strange UFO sighting. These are amongst the most common things that that Lenticular clouds are mistaken for.
Lenticular clouds, or Altocumulus lenticular, are lens shaped clouds that form at high altitudes due to specific interactions with wind flow. These clouds get their name due to their flat, pancake-like shape from the word ‘lenticularis’, which in Latin means ‘lens’.
So, where do they come from and how exactly do they form?
Fig.1 : Lee Waves Author: Dake via Wikimedia Commons
These fascinating clouds form when stable moist air comes into contact with, and flows over mountains or other barriers. This causes waves known as as lee waves to form on top of the mountain, as well on the leeward side of the mountain or barrier. Lecnticular clouds form at the crest of each of these waves (points A and B in Fig. 1) provided that the air contains enough moisture, and the temperature drops to, or below the dew point of water. These two conditions are crucial to their formation! Once these conditions are met, the moisture condenses, and results in the formation of these amazing clouds!
As harmless as they look,they serve as a reminder that looks can be deceiving. This is because great turbulence is generated from rotor waves, which form in the vicinity of lenticular formations, specifically around lee waves. Rotor waves are a sure indication of high velocity, extremely turbulent air circulation, and very unstable conditions. Therefore, flying near these clouds is usually avoided.
Brandy Jenkins via Wikimedia commons
Lenticular clouds are classified into three categories primarily based on the height of their formation. The lowest forming Lenticular cloud is known as Stratocumulus Standing Lenticularis (SCSL) which is found at elevations of about 8000 feet.
Between 8000 to 20,000 feet high, the Altocumulus Standing Lenticularis (ACSL) is found, which is the most common type of Lenticular cloud. One of the distinctive features of ASL that separates it from the two other types, is that it tends to be stationary. The lenticular clouds shown in the video below are most likely ASL clouds as they appear to be frozen, as other clouds pass by them.
Above: Video showing a time-lapse of Lenticular clouds (Credit: Soaring Nv)
Finally, the highest forming Lenticular cloud is the Cirrocumulus Standing Lenticularis,(CCSL) which form at elevations above 24 000 feet. These are very rare however, as few mountains exist as such high altitudes.
Usually mistaken for being a product of photoshop, Lenticular Clouds represent one of our worlds most extrodinary phenomenons, and continue to fascinate thousands of people with their presence, marked by uniquely defined beauty.
-Tabish Khan
