Human Cloud Iridescence imaged in Hungary by Mónika Landy-Gyebnár.   
©Mónika Landy-Gyebnár

To capture the iridescence you will need to have a cold day, to look against the light and to have a patient volunteer who will breathe out slowly and gently.

Mónika's image neatly captures the mechanism of a major source of skyward iridescence. Warm, moist air is quickly cooled, in this case by admixture with much colder air. Water vapour condenses into tiny water droplets that then diffract sunlight.

In clouds, the rapid cooling mostly occurs when air is forced upwards causing it to expand and adiabatically cool.

Pileus cloud iridescence is the result of a moist air layer air forced upwards by lower cumulus.

Lenticular clouds form at the high points of up and down wave motion of air in the lee of mountains or other disturbances.

Banner clouds on mountain peaks are in part the result of warmer moist air induced to flow upwards where it expands and cools.

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