Smooth, stationary clouds are occasionally reported by the public as sightings of “unidentified flying objects.” But these clouds are not as mysterious as they might first seem.
On December 29, 2020, the Operational Land Imager (OLI) on Landsat 8 acquired these images of soft-edged clouds hovering over the Eisenhower Range of Antarctica’s Transantarctic Mountains. The range is bounded to the north by Priestley Glacier and to the south by Reeves Glacier, both of which feed into the Nansen Ice Shelf on Terra Nova Bay.
The clouds have the hallmarks of lenticular clouds that can form along the crests of mountain waves. Mountain waves form when fast moving wind is disturbed by a topographic barrier—in this case, the Eisenhower Range. Air is forced to flow up and over the mountains, causing waves of rising and falling air downwind of the range. The rising air cools and water vapor condenses into clouds. Conversely, falling air leads to evaporation.
Adding to their mystique, this cloud type appears to stay put—sometimes for hours—defying the strong horizontal winds. In reality, the clouds are constantly building around the crest of the wave and then dissipating just beyond.
In the United States, lenticular clouds are particularly common around the Rocky Mountains. They have been known to occur over Antarctic mountains, too, but there are not many witnesses besides satellites. The white-on-white color of clouds over ice make the Antarctic versions harder to discern, even in satellite images. This natural-color image has been enhanced with infrared light to separate the white clouds from the white snow and ice below. The clouds also threw rounded shadows on the landscape.
Still, a few people have witnessed lenticular clouds in Antarctica firsthand. Scientists working with NASA’s Operation Icebridge shot photos of the phenomenon near Mount Discovery in 2013 and over Penny Ice Cap in 2015.
NASA Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen with image interpretation by Bastiaan Van Diedenhoven (NASA GISS/Columbia) and Jan Lenaerts (CU Boulder).
Something I have never explained: A friend and I were hitching a ride to town, in the back of a pickup truck, traveling in a north south lake valley with steep mountains to the east & west. I saw the beginning of a perfectly elliptical cloud start coming over the mountain to the west. It continued onward, and when it was half visible I saw the beginning of another one. We watched until two of these clouds were fully visible, with flawless oval shapes, and almost identical in size. We tapped on the truck roof to get the driver & his cab mate to stop and look, and in the end all 4 of us watched these clouds until they disappeared over the mountains on the east side of the lake. Then we looked at each other, scratched our heads, and continued on to town! What were they? I have no idea….