My book tells me that altocumulus lenticularis are not moved by wind but rather the air just flows through them without effect on their position. How come they are the only cloud type that is stationary?


1 Answer 1


Clouds form when particular conditions of temperature and humidity intersect.

In the case of lenticular clouds, those conditions occur at specific locations slightly downwind from the tops of mountains -- a standing wave forms in the air between areas of low and high humidity, much as standing waves form in river rapids. Niobrara standing waves

Source: National Park Service

The standing waves can only form when wind is blowing over the mountain, and so the region of air where the standing waves create the conditions to form clouds is pinned down by the mountain.

The region doesn't move, but the air and water molecules do.

  • New moist air blows over the mountain, following the standing wave, and into a zone of lower temperature, where it condenses into the droplets that form the cloud.

  • Still following the wave, the droplets blow into an area of higher temperature and evaporate again.

enter image description here

Source: National Weather Service

Also, the standing waves that guide moist air to form lenticular clouds are an example of laminar flow.

Other clouds appear to move because and the air where they form is moving turbulently, and they are also not controlled by temperature (they move within a layer about the same temperature), only moisture.

  • 4
    $\begingroup$ Great answer. Or put it this way: the air is indeed advecting the cloud material (it always does). But that wind is unendingly sinking as it goes forward, and so the cloud is continually dissipating downwind. The cloud is a perpetual factory, made by the wind and dissipated by the wind $\endgroup$ Commented Aug 6, 2023 at 21:53
  • 3
    $\begingroup$ A similar effect, but near a moving "mountain" happens around high-speed vehicles: vapor cone. $\endgroup$
    – Ruslan
    Commented Aug 7, 2023 at 19:50
  • 3
    $\begingroup$ @Ruslan That is caused by the pressure decrease due to the dynamics and is hence closer to banner clouds rather than these wave clouds. $\endgroup$ Commented Aug 8, 2023 at 11:57

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