GlossaryHomogenitus
Special origin · High
Homogenitus
homogenitus
Definition
A cloud whose formation is directly caused by human activity, most commonly an aircraft contrail. The suffix was introduced in the 2017 revision of the atlas and is usually attached to the parent genus, as in cirrus homogenitus.
Field note
Whether a contrail becomes cirrus homogenitus depends entirely on the humidity of the ambient air. Persistent, spreading contrails therefore amount to a free measurement of ice supersaturation in the upper troposphere.
- Added
- 8 August 2026
- By
- Class
- Special origin
- Band
- High
Read the full field note
Contrails: reading the sky for aviation weather clues
A contrail is a cirrus cloud that would not exist without an aircraft. The World Meteorological Organization formalised this by giving them the name cirrus homogenitus — 'man-made cirrus'. They are worth observing carefully, because whether a contrail persists or vanishes within seconds is one of the best free measurements of upper-level humidity available to anyone on the ground.