Corona + Iridescence

Last updated on September 16, 2023

Corona + Iridescence: A Captivating Atmospheric Phenomenon

When we gaze up at the sky, we are often treated to an array of captivating sights. One such spectacle is the combination of corona and iridescence. These two atmospheric optics phenomena can create a stunning display of colors and rings surrounding the sun. While coronas are relatively common, the simultaneous presence of iridescence adds an extra layer of beauty and intrigue to the scene.

A corona is formed when sunlight passes through tiny cloud droplets. These droplets diffract the light, causing it to spread out and create a bright aureole around the sun. The corona itself consists of concentric rings of varying intensities. The size and uniformity of the cloud droplets play a crucial role in determining the appearance of the corona. When the droplets are uniform in size, a well-defined corona with clear rings is formed.

Cloud iridescence, on the other hand, occurs when the cloud droplets have varying sizes throughout the cloud. This creates a more disordered pattern of colors, reminiscent of a pastel palette. The changing drop sizes result in diffraction patterns that produce the beautiful hues of iridescence. These patches of color can appear alongside the corona, enhancing the overall visual spectacle.

One might wonder why newly formed clouds often exhibit both corona and iridescence. The answer lies in the history and size distribution of the cloud droplets. In newly birthed clouds, the droplets have similar histories and sizes, which are necessary for the diffraction colors to remain distinct and not blend into white. As the cloud matures and evolves, the droplet sizes become more varied, leading to the emergence of iridescence alongside the corona.

To truly appreciate the intricate details of corona and iridescence, a closer look is warranted. Upon zooming in, the circular coronal rings start to merge into a more disordered display of iridescence. This transition showcases the gradual shift from the well-defined rings of the corona to the ethereal and whimsical colors of iridescence. The interplay between these two phenomena creates a visual feast for the eyes.

In conclusion, corona and iridescence are two atmospheric optics phenomena that, when combined, produce a breathtaking spectacle in the sky. The diffraction of sunlight by cloud droplets gives rise to these mesmerizing displays of color and rings. While coronas are more commonly observed, the presence of iridescence adds an element of disorder and pastel beauty to the scene. The size and uniformity of the droplets determine whether a corona or iridescence will dominate the view. So, the next time you find yourself beneath a newly formed cloud with thin diffuse clouds, take a moment to look up and marvel at the magical dance of corona and iridescence in the sky.

Iridescence & Corona

A scene by Marco Meniero at Viterbo, Italy. The sun shines through thin diffuse cloud, likely newly birthed. Surrounding the sun is an intensely bright aureole circled in turn by delicate coloured rings. A corona.

A corona is a common enough sight. Less common are the simultaneously surrounding patches of colour. Cloud iridescence.

Diffraction of sunlight by tiny cloud droplets made them both. The differences comes from the droplets themselves. Uniform sized droplets produce a corona. Clouds with changing drop size from place to place give the more disordered but beautiful pastel hues of iridescence. Why newly birthed clouds? Droplets in newly formed clouds have the same history and very similar sizes necessary for the diffraction colours not to be blurred out to white.

This close up shows less circular coronal rings merging into disordered iridescence.

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Reference Atmospheric Optics

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