They're Here... We're All Doomed!

[River]

These cloud photos were taken over Brisbane yesterday... A most unusual sight indeed..!

 

I looked up weather photos on the web and appears this is what we were looking at.

 

"Fallstreak hole

 

From Wikipedia, the free encyclopedia

 

A fallstreak hole, also known as a hole punch cloud, punch hole cloud, skypunch, canal cloud or cloud hole, is a large circular or elliptical gap, that can appear in cirrocumulus or altocumulus clouds.

 

Such 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 ice nucleation particles (see supercooled water). When ice crystals do form it will set off a domino effect, due to the Bergeron process, causing the water droplets around the crystals to evaporate: this leaves a large, often circular, hole in the cloud.

 

It is believed that the introduction of large numbers of tiny ice crystals into the cloud layer sets off this domino effect of evaporation which creates the hole.

 

The ice crystals can be formed by passing aircraft which often have a large reduction in pressure behind the wing- or propellor-tips.

 

This cools the air very quickly, and can produce a ribbon of ice crystals trailing in the aircraft's wake.

 

These ice crystals find themselves surrounded by droplets, grow quickly by the Bergeron process, causing the droplets to evaporate and creating a hole with brush-like streaks of ice crystals below it.

 

The articles by Westbrook and Davies (2010) and Heymsfield et al. (2010) explain the process in more detail, and show some observations of their microphysics and dynamics. Such clouds are not unique to any one geographic area and have been photographed from many places.

 

Because of their rarity and unusual appearance, as well as very little exposure in media, fallstreak holes are often mistaken for or attributed to unidentified flying objects."

 

 

 

 

[bexrbetter]

....... are often mistaken for or attributed to unidentified flying objects."

Seems logical.

 

By the way, that's a paradox, "unidentified flying objects" are actually identified - as unidentified flying objects!

 

 

[facthunter]

Supercooled water (below 0 degrees C) in vapour form, needs condensation nuclei for the change of state to occur (Dust or ice particles etc will work as the nuclei). The energy relating to the phenomenon is the latent heat of vaporisation which occurs as a change of state ( in this case from gas to liquid, or vice -versa). From liquid to gas, heat must be added ( evaporation cools) and the other way around it is given out by the process. THIS ALONE is responsible for the intense energy of cyclones and the energy level is highest when the ambient temps are high and maximum moisture is present. (High relative humidity). Also the rapid updrafts in large cumulonimbus clouds, holding vast amounts of water and sometimes forming large hailstones that may fall 20 kms downwind of the cloud.. Nev