A persistent cloud structure intrigues observers. It has reappeared in the same place for over a century. But why? Named the
Taieri Pet, this misty mass has hovered above Otago's mountains in New Zealand since 1896.
Photographed by NASA on October 7, 2024, this lenticular cloud is often mistaken for a UFO. Its elongated shape, reminiscent of a flying saucer, fuels this myth.
The rugged terrain of New Zealand's South Island gives rise to this distinctive lenticular cloud formation, locally known as Taieri Pet.
In reality, the appearance of the Taieri Pet is linked to specific meteorological phenomena. Altocumulus lenticularis form when fast-moving winds encounter an abrupt obstacle, such as a mountain range.
In the case of this cloud, the Rock and Pillar chain plays a key role. Strong northwesterly winds strike it, creating undulations that condense the air into stationary clouds. These appear smooth with sharp edges. From the ground, their disc-like appearance evokes "piles of pancakes" or "flying cigars," according to the National Weather Service.
New Zealand meteorologist John Law explains that this phenomenon is shaped by intense crosswinds. The cloud appears stationary, though it is the result of strong currents.
For aviation, such clouds represent a real threat. They cause turbulence and can ice up aircraft due to the rapid thermal changes they induce.
Why don't lenticular clouds move?
Lenticular clouds seem stationary, but they are constantly forming and reforming in specific areas. This happens when strong winds, encountering a mountain, create an upward and downward air wave, causing moisture to condense into a fixed cloud at that precise spot.
The structure of lenticulars remains stable because the air flows through the cloud without displacing it. Moisture condenses as it reaches the crest of the wave, forming the cloud, and evaporates as it descends. This continuous loop allows the cloud to maintain its apparent position.
To the observer, this phenomenon gives the impression of a cloud frozen in the sky. In reality, it's a constant cycle of formation and dissipation that keeps this cloud seemingly "immobile."
What dangers do lenticular clouds pose for aviation?
Lenticular clouds pose several risks for aviation due to their unique formation and atmospheric characteristics. Their appearance often indicates strong winds at high altitude, which can generate severe turbulence nearby. Aircraft passing through these areas may experience sudden air variations, making control more difficult.
Additionally, moisture condensation within these clouds can cause aircraft icing. This buildup of ice on wings and critical surfaces reduces the efficiency of the aircraft and can compromise flight safety. Pilots must, therefore, remain vigilant and avoid areas where these clouds are present.
Finally, lenticular clouds can mask more severe weather conditions, such as thunderstorms, making detection and anticipation more difficult for pilots. This highlights the importance of meteorological monitoring during flights near mountains and other topographical obstacles.
Article author: Cédric DEPOND