Category Archives: Crepuscular Rays

Growing cumulus in Ontario

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Lynnkarl Karst
Location: Innerkip, Ontario
Date: 28 June 2014

On a warm summer day, cumulus clouds form as sun-heated surface air rises. As the air rises, it cools, eventually to its dewpoint temperature where the air saturated, above which condensation occurs to form a cloud. As long as the air stays warmer than its environment, it will continue to grow to be cumulus congestus clouds, as are seen in this picture over Ontario, Canada.

When the clouds block the sun, alternating rays of light and shadows are observed, referred to as crepuscular rays. As the sun continues to set, the sun’s rays have to pass through more of the atmosphere, where the shorter wavelengths of the visible spectrum (the blues) are scattered away, leaving the pinks/oranges/reds to color the clouds late in the day.

Illuminated congestus along the Gulf of Mexico

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Jason Taylor
Location: Mississippi Gulf Coast
Date: 26 June 2014

Warm, moist air from the Gulf of Mexico fuels growing cumulus congestus clouds along the Mississippi Gulf Coast and beyond. This picture shows an absolutely beautiful example of this! The sun illuminates the clouds while the clouds block the sun to create upward-directed crepuscular rays.

Beautiful mix of clouds in Norway

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Hanne Pernille Ryel
Location: Bj├Şrnemyr, Norway
Date: 27 June 2014

Wow, what a mix of clouds over Norway in this picture! At the highest levels, cirrus clouds smear the sky as the wind carries the ice crystals, while mid-level altocumulus clouds spread out across the sky with their darker appearance creating a great contrast against the cumulus clouds being illuminated by the setting sun. These clouds block the sun to create upward-directed crepuscular rays! Crepuscular means “referring to twilight”, which is appropriate as it forms in the waning daylight hours over Norway. This mixture of clouds indicates moisture at many levels and if, especially, the mid-level cloud layer continues to increase in coverage across the sky, it could mean more inclement weather in store.

Crepuscular rays over the UK

When clouds block the sun, alternating rays of light and shadows can appear to radiate from the top or bottom of the clouds. These are called Crepuscular rays where crepuscular is Latin for “relating to twilight.” This is an appropriate name because the rays are often seen when the sun is at a lower angle in the sky, around sunrise or sunset; although, this doesn’t always have to be the case. They are actually parallel rays of light but appear to radiate outward due to perspective. In this photo,the rays and sunlight help to illuminate the well-defined, puffy tops of the cumulus clouds below.

Nicky Clarke
Location: Manchester, UK
Date: 18 June 2014

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