Cloud of the Day – Cirrus Homogenitus
In the past, meteorologists refused to include human-made phenomena in their classifications of cloud types. Yes, they said, the steam and smoke coming out of our smokestacks can appear like clouds or fog, but they’re not really. While weather observers might observe reduced visibility and even attribute it in part to our activities, there was no place for them on the reporting forms. If they were going to mention smog or condensation trails, it would be in the comments only. In the case of condensation trails, they became abbreviated in common language as “contrails.” On the reporting forms they appeared in the comments section as “COTRA.”
Now, with the updating this year of the International Cloud Atlas, hosted by the World Meteorological Organization, as reported on the Green Comet blog, a number of new cloud types have been included. I’ve already reported on asperitas, volutus and flumen, which are natural cloud types that have been included in this edition of the Atlas. Today I present another inclusion, this time a cloud type that results from human activity: cirrus homogenitus. Literally, cirrus made by humans. Condensation trails can now come out of the comments and take their rightful place in the form proper.
Cirrus homogenitus is the new name for contrails that have persisted for at least ten minutes. It comes in the one type only, with no sub-types or varieties. That’s because contrails are usually quite ephemeral and either disappear or change rapidly.
Cirrus homogenitus are like other cirrus clouds in that they don’t result in any precipitation or other weather. Unlike cirrus, they can’t even be credited with foretelling the approach of a weather system. They’re just the result of an airplane flying in the stratosphere, portending nothing more than its arrival, hopefully at its destination.