Denver Wave Cloud Iridescence

Last updated on September 16, 2023

Denver Wave Cloud Iridescence: A Spectacular Atmospheric Phenomenon

Have you ever seen iridescent wave clouds in the sky and wondered how they form? These mesmerizing displays of colors, reminiscent of stratospheric nacreous clouds, are a rare sight, especially when the sun is shining brightly. In this article, we will explore the fascinating phenomenon of Denver wave cloud iridescence and delve into the science behind their formation.

Unlike their stratospheric counterparts, which require extremely cold temperatures of around -85 degrees Celsius, these wave clouds over Denver, Colorado, are more likely found at lower altitudes and warmer temperatures. Their formation is attributed to the airflow over the nearby Rocky Mountains, which induces vertical wave motion in the lee of the mountains.

When air flows over the Rockies, it encounters variations in terrain and atmospheric conditions. As a result, wave-like patterns are created in the atmosphere. These waves consist of rising and descending air pockets, which play a crucial role in the formation of the iridescent wave clouds.

In a rising section of the wave, an air pocket expands and cools. This cooling leads to the condensation of droplets within the pocket. These droplets have near-identical histories and tend to be of similar sizes within specific areas of the cloud. As sunlight passes through these droplets, they scatter and diffract the light, giving rise to the ethereal colors observed in iridescent wave clouds.

However, the phenomenon does not end there. As the air pocket subsequently descends, it heats up again, causing the droplets formed just moments earlier to evaporate. This constant cycle of condensation and evaporation within the cloud creates a dynamic environment where the colors seem to shift and change with time.

The iridescence observed in these wave clouds is a result of a process known as thin-film interference. When sunlight encounters the tiny droplets in the cloud, it interacts with the droplet's surface and undergoes constructive and destructive interference. This interference causes certain wavelengths of light to amplify or cancel each other out, resulting in the vibrant array of colors that captivate our eyes.

It's important to note that the appearance of iridescent wave clouds is highly dependent on various factors, such as the size and distribution of the droplets, the angle of sunlight, and the observer's position. This variability contributes to the unique and ever-changing nature of these atmospheric phenomena.

In conclusion, Denver wave cloud iridescence is a captivating display of colors in the sky, brought about by the interplay of rising and descending air pockets within wave clouds. The condensation and evaporation of droplets, coupled with thin-film interference, give rise to the enchanting hues that adorn the clouds. Next time you find yourself gazing at the sky and spotting these iridescent wonders, take a moment to appreciate the intricate processes at play and marvel at the beauty of our atmosphere.

Iridescent Wave Clouds, Denver, Colorado ~ Image by Silvia Maria February 10, '08. ©Silvia Maria, shown with permission.

These look for all the world like stratospheric nacreous clouds but that cannot be. They are rarely seen so bright when the sun is up and the stratosphere over Denver would have to be very unusually cold indeed. A temperature of -85 Celsius is needed that is sometimes attained in Polar and near polar regions.

These Denver wave clouds are more likely lower and warmer. Airflow over the Rockies induces vertical wave motion in their lee.

An air pocket in a rising section of wave expands and cools. Droplets condense.

As the air pocket subsequently descends it heats again and the droplets formed only seconds earlier evaporate.

Clouds of droplets with near identical histories have similar sizes in particular areas of the cloud. They scatter and diffract sunlight to produce these filmy colours.

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Reference Atmospheric Optics

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