Now for a little follow-up (in case we didn’t cover it in enough depth previously). A couple summer’s ago a strange cloud phenomenon developed over Mosinee and Stevens Point. Several people mailed in pictures of what looked like 3 perfectly formed holes in a thin layer of clouds. At the time I speculated there might have been some sort of precipitation that formed in those areas of the clouds (and took the moisture out) or that air craft had somehow formed the circles. Follow this link to see a similar (very cool ) picture taken earlier this year.

It turns out that the holes were most likely created by airplanes. The cloud formation is called a “hole punch”. It is not so much created directly by an airplane flying through a cloud (otherwise the “hole” would look more like an X or cross) but by the exhaust from the jet engines. In the right type of thin cloud where the moisture is near the point of becoming precipitation, the exhaust from a jet engine can cause the cloud droplets to become raindrops (or snow) and start falling. When the precipitation falls, it leaves an empty hole in the cloud (because it is quite thin). This only happens when an airplane is ascending or descending rapidly through the could. If it was flying parallel to the cloud layer then we might just see a line through the clouds or a contrail-type formation.

So why would it be in the shape of a circle or oval/ellipse? It is because the exhaust from the jet engine extends behind the plane in the shape of cyclinder (before it is eventually dispersed by the wind). Why don’t we see “hole punches” more often? Because the conditions have to be just right. If the clouds are too thick, the air too moist/dry, or the winds too strong, then we wouldn’t see such perfect holes.

Have a pleasant Thursday! Meteorologist Justin Loew.

Posted under Nature