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From: Dan Richter (1:317/3)
To: All
Date: Mon, 14.06.21 13:00
ES Picture of the Day 14 2021
EPOD - a service of USRA

The Earth Science Picture of the Day (EPOD) highlights the diverse processes
and phenomena which shape our planet and our lives. EPOD will collect and
archive photos, imagery, graphics, and artwork with short explanatory
captions and links exemplifying features within the Earth system. The
community is invited to contribute digital imagery, short captions and
relevant links.

Fall-streak and Circumzenithal Arc

June 14, 2021


Photographer: Marco Meniero

Summary Author: Marco Meniero

Featured above is a colorful circumzenithal arc and a
fall-streak observed from Civitavecchia (Rome), Italy, below the
approach path of the Fiumicino Airport. Fall-streak holes occur in
cloud decks ( altostratus clouds, for example) where the droplets of
liquid water that compose them are in a supercooled state; that is
they remain in liquid even if the air temperature is well below the
freezing point of water (0 ° C). However, an aircraft passing through
the cloud layer can cause the supercooled droplets to suddenly freeze,
resulting in a cascade of ice crystals. When these crystals become
sufficiently heavy, they’ll detach from the cloud and fall, leaving a
void in the cloud layer – a hole in the sky. In this case, the
falling crystals were oriented so that sunlight entered their uppermost
horizontal faces and exited through one of their vertical side faces,
forming this charming circumzenithal arc. Note also the cloud
iridescence near the bottom of the photo.

Both climbing and descending aircraft will trigger fall-streaks in
shallow cloud decks, which explains why such voids are often seen in
the vicinity of busy airport runways. Photo taken on April 12, 2021.
* Fiumicino Airport, Italy Coordinates: 41.7999,12.2462

Related EPODs

Fall-streak and Circumzenithal Arc Archive - Red Rose and
Morning Dew Northern Lights Above the Lofoten Islands of Norway
Sunrise and Sunset Skies Strong Storms Over the Olympic
Mountains Surprise on the Tyrrhenian Sea

Atmospheric Effects Links

* Atmospheric Optics
* Color and Light in Nature
* The Colors of Twillight and Sunset
* Refraction Index
* Image Gallery: Atmospheric Effects
* What is a Rainbow?

Earth Science Picture of the Day is a service of the Universities
Space Research Association.
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