Hole in Cloud Mystery
June 07, 2002
The marvelous photo above shows why looking up now and then can be rewarding. Cumulus cloud types (cumulus humilus, cumulus fractus and cumulus congestus clouds) fill up the lower portion of the picture, but the centerpiece of the photo is the donut-shaped altocumulus cloud. Note the iridescent nature of this cloud, which means that it's likely less than about 40 degrees away from the Sun. Iridescence results from diffraction - deflection of light around objects, water droplets for instance. For a hole to occur in a cloud, some process must be at work to remove the cloud droplets or crystals. For example, if a cloud is seeded with silver iodine or carbon dioxide, a hole could occur in a portion of the cloud deck. In this case thought, the hole is more perpendicular than parallel to the ground surface, so it's unlikely that it results from seeding. Also, note the jet contrail and its shadow to the left of the donut cloud. Although, it appears the jet pierced the hole, it couldn't have caused the hole to form in a fraction of a second.