Arctic Halos

Last updated on September 16, 2023

Arctic Halos: A Stunning Atmospheric Phenomenon

Arctic halos are a captivating atmospheric optics phenomenon that enchants viewers with their ethereal beauty. These optical phenomena occur in the polar regions, where the extreme cold temperatures create the perfect conditions for the formation of ice crystals in the air. The intricate interplay between sunlight and these ice crystals gives rise to a mesmerizing display of halos, sundogs, and other celestial spectacles.

When observing the Arctic skies, one may encounter tall sundogs flanking the sun. These sundogs, also known as parhelia, are formed by the refraction and reflection of sunlight by plate-shaped ice crystals suspended in the atmosphere. The shape of these sundogs is determined by the locations of layers of diamond dust crystals, creating an awe-inspiring sight.

However, distinguishing between tall sundogs and a 22° halo can sometimes be challenging. Plate crystals with large wobbles can result in sundogs with such significant distortions that they closely resemble a 22° halo. In essence, the line between these two phenomena becomes blurred, making it an intriguing topic for further exploration.

The Formation of Arctic Halos

To truly appreciate the beauty of Arctic halos, it is essential to understand their formation process. These atmospheric marvels come to life through a series of intricate interactions between sunlight and ice crystals in the atmosphere. Here's a breakdown of the key steps involved:

1. Ice Crystal Formation: In the frigid Arctic air, tiny ice crystals form as water vapor freezes onto existing particles, such as dust or salt particles. These ice crystals can take various shapes, including plates, columns, and needles.

2. Orientation and Alignment: As the ice crystals fall through the air, they become aligned with their flat faces parallel to the ground due to air resistance. This alignment is crucial for the subsequent optical phenomena.

3. Refraction and Reflection: When sunlight passes through these aligned ice crystals, it undergoes refraction and reflection. Refraction occurs as the light bends when transitioning from one medium (air) to another (ice crystal). Reflection, on the other hand, involves the bouncing back of light rays from the surfaces of the ice crystals.

4. Halo Formation: The refraction and reflection of sunlight within the ice crystals give rise to a range of optical phenomena, including halos, sundogs, and arcs. These phenomena occur at specific angles and positions relative to the observer and the light source, resulting in their characteristic shapes and locations in the sky.

The Enigmatic Tall Sundogs

Tall sundogs, with their elongated appearance, add an element of mystique to the Arctic halo spectacle. These sundogs are formed by plate-shaped ice crystals that possess larger wobbles or deviations from their ideal orientations. As a result, the light passing through these crystals is refracted and reflected in a way that creates tall columns of light on either side of the sun.

The distinction between tall sundogs and a 22° halo can sometimes be indistinct, blurring the line between the two phenomena. When the wobbles of the plate crystals are particularly large, the sundogs can closely resemble a 22° halo, making it challenging to differentiate between the two. This intricate interplay between crystal orientation and light refraction adds an extra layer of complexity to the study of Arctic halos.

Exploring Arctic Halo Variations

While tall sundogs and 22° halos are two prominent features of Arctic halos, they represent just a fraction of the diverse range of atmospheric optics phenomena that can occur in polar regions. Some other captivating variations include:

• Circumzenithal Arc: This vibrant arc appears as an upside-down rainbow located above the sun. It forms when sunlight refracts through horizontally oriented ice crystals.

• Supralateral Arc: The supralateral arc is a rare and elusive phenomenon that appears as an arc of light extending horizontally from the sundog. It occurs when sunlight undergoes internal reflection within horizontally oriented plate crystals.

• Diamond Dust: Diamond dust refers to the presence of tiny ice crystals in the air, often resembling glittering diamonds suspended in the atmosphere. These crystals can create a mesmerizing display of halos, arcs, and other optical phenomena.

The Scientific Significance

Arctic halos not only captivate our senses but also provide valuable insights into the properties of ice crystals and the physics of light. By studying these atmospheric phenomena, scientists can gain a deeper understanding of the microphysical processes occurring in the polar atmosphere. This knowledge is crucial for climate research, weather forecasting, and advancing our understanding of Earth's delicate energy balance.

Through detailed observations and measurements of Arctic halos, scientists can gather data on ice crystal shapes, orientations, and sizes. This information helps refine models and simulations that aim to accurately represent the behavior of light in icy atmospheres. Such research contributes to improving our understanding of various optical phenomena in diverse environments, from the Arctic to other regions of the world.

In conclusion, Arctic halos are a captivating manifestation of the interplay between sunlight and ice crystals in the polar atmosphere. From tall sundogs to intricate halo variations, these optical phenomena offer a visual feast for those fortunate enough to witness them. Exploring the formation processes and distinguishing between different halo types adds depth to our understanding of atmospheric optics. As scientists continue to unravel the secrets of Arctic halos, we gain valuable insights into the physics of light and the delicate balance of our planet's atmosphere. So, keep your eyes on the skies and be prepared to be dazzled by the magic of Arctic halos.

Arctic Halos by Tom Morgan January '08. Image ©Tom Morgan, shown with permission.

Tall sundogs flank the sun, their shape set by the locations of layers of diamond dust crystals.

Or are they parts of a 22° halo? Tall sundogs result from plate crystals with large wobbles. When wobbles are very large the distinction between tall sundogs and a 22° halo becomes rather academic.

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