One of the most striking cloud formations that skywatchers might see is the cavum. When viewed from below, they can resemble a big circle or ellipse precisely sliced out of cirrocumulus or altocumulus clouds, leaving just a few sparse wisps of cloud in the center.
However, these clouds are even more eye-catching when viewed from above. Luckily for us, NASA's Earth Observatory (EO) captured a satellite view of a long cavum encompassing a portion of southeast France on Jan. 14.
The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite captured the image in natural color to highlight some of its details.
On January 14, 2023, this satellite view shows a long cavum encompassing a portion of southeast France. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite captured the image in natural color. Cavum, also known as hole-punch clouds and fallstreak clouds, develops when an airplane passes through a layer of cloud, which causes atmospheric instability and frigid air temperatures.NASA Earth Observatory/ Adam Voiland
Hole-Punch Clouds
According to NASA, Cavum is also known as hole-punch clouds and fallstreak clouds. The cloud forms when an aircraft passes through a layer of cloud, which causes atmospheric instability and frigid air temperatures.
When viewed from below, it could seem as though a portion of the cloud is tumbling from the sky, and this is what exactly occurs within the formation.
Hole-punch clouds are mid-level clouds made up of super-cooled liquid water droplets, which means the droplets are still liquid at temperatures below the water's ordinary freezing point (32°F, or 0°C). However, NASA notes that even extremely chilled droplets have a limit.
The additional cooling that transpires, for example, over the aircraft's wings as it passes through the cloud layer, can cause the droplets to become frozen.
For instance, when an airplane flies through the cloud layer, the additional cooling over the aircraft wings may cause the droplets to become frozen.
The liquid droplets continue to freeze, producing more and more ice crystals. Eventually, they become so heavy that ice crystals fall from the sky, causing a hole in the cloud cover.
Virga, or wispy precipitation trails, are characteristics that are frequently seen at the center of the holes where the ice crystals are falling.
Small, circular cavum is created when planes fly at a fairly sharp angle through clouds, according to NASA.
They can create long "canal clouds" with extended virga trails if they enter the clouds at a shallow angle, which is exactly the case for this cloud formation that NASA's EO captured.
The space agency also noted that the amount of cloud cover, air temperature, and the degree of horizontal wind shear could all impact how long this particular cloud formation lasts.
