Cool cloud produces alien image When Jonathan Sabin emailed us with this terrific cloud image, we jumped at the chance to find out what created it. So we contacted Jeff Callaghan, severe storm forecaster with the Bureau of Meteorology in Brisbane, Australia. I've never seen anything like this - due to it's symmetry, and the fact that it appears as if it were 'dropped' into place, it doesn't seem like a natural formation.
Ice crystals form and they grow at the expense of the super cooled water drops.
This is called glaciation and refers to the sudden transformation of super cooled cloud droplets into ice crystals. The glaciated cloud lowers the vapour pressure around its edges which evaporated the super cooled cloud droplets giving the sharp edge to the cloud. All clouds above the freezing level contain super cooled water drops at some stage and altocumulus is predominately made up of super cooled water drops well below zero.