Fallstreak hole

A fallstreak hole or cloud hole is a large, roughly circular opening that can appear in Cirrocumulus or Altocumulus clouds. These holes are formed when the water temperature in the clouds is below freezing, but the water has not frozen yet due to the lack of nucleation of the ice particles.

When a portion of water begins to freeze, it triggers a domino effect, causing the vapor around it to freeze and thus fall to the ground. This leaves a large, often circular, hole in the cloud.

The holes also usually have clouds at the same level or lower, usually Cirrus, in the central region, in the form of a virgin. One explanation would be that the precipitation that causes the hole creates a new decompression as it falls, with the vacuum drawing the nearby clouds to the center and down. Another explanation is that the disturbance caused by precipitation would somehow generate new clouds.

These theories try to explain how holes are formed, but do not clarify what produces them (which triggers the precipitation of only part of the steam and ice). This nuisance is not new, and there is some consensus that the cause must be some external disturbance.

In 1968, a photograph of this hole generated considerable interest in the US Meteorological Community and sparked a series of speculations about its cause.

Most of the proposed mechanisms focused on what some atypical pattern of evaporation could have occurred, including the descent of air remaining from the eye of a hurricane and the local warming of air on dissipation trails, passing meteors, or heat from passing a plane through. jet.

It has also been suggested that jet inversion channels may be a source of ice particles that would grow with pre-existing cloud droplets.

Many dissipation trails and fallstreak holes are photographed by satellite in regions of high air traffic. The aircraft displacement vacuum creates conditions for precipitation of only part of the suspended material, although the reasons for this have not yet been precisely identified.

As for the clouds in the central part of the hole, they also leave questions. Sometimes they extend deep into the ground, as if something denser than rain has plunged into the ground through the cloud curtain.

Other times, their composition is considerably different from those around the formation, suggesting that they were not attracted to the position or too high to show that the initial precipitation formed them.

Scientists explain that when a plane passes clouds below -10 ° C, called super cold by the researchers, the effect of the propellers may be enough to spontaneously freeze the small drops of water from the cloud and form ice crystals that grow as they grow larger. drops are joining the “ice ball”. It is precisely this chain reaction of ice crystal formation, which can last several hours after a plane passes, that gives way to the holes in the clouds.