An Icy Existence

First observed and documented in the late 1880s, the clouds are made of ice crystals that form “at the edge of space itself” — or 80-85 kilometers (53 miles) above the Earth’s surface, in regions nearest the North and South poles.

Seen only at twilight, they are said to be ‘night-shining’ clouds because they exist at such high altitudes that they reflect the sun’s light after it has set below the horizon.

It was actually back in 1962, when B.W. Currie — the preeminent Canadian expert in meteorology and climatology at the University of Saskatchewan — called for formal studies of noctilucent clouds in a paper for the Royal Astronomical Society of Canada. Scientists, he said, were especially interested in determining how the clouds form, and why they were seen more often over Europe than North America.

Because temperatures and other conditions at that altitude made it unlikely for the ice crystals to form on their own, it was more likely that the ice was clinging to something in the atmosphere, possibly volcanic ash or particles leftover from meteors. If so, the appearance of the clouds should correlate with meteor showers, Currie wrote in his paper.

While the presence of volcanic ash has since been discounted, NASA launched a satellite in 2007 to study the clouds and their role as possible harbingers of change in the atmosphere and Earth’s climate. Called the Aeronomy of Ice in the Mesosphere (or the AIM mission) the study has shown that the crystals are most likely formed on meteoric dust, that they are exclusively a summertime event, and that the cloud formations change year-to-year, a process scientists “believe is intimately tied to the weather and climate of the whole globe.”

 

Cloud Patterns

More notably, scientists have learned that events in one hemisphere “can have a sizeable effect in another,” according to NASA. By tracking wind and other atmospheric patterns around the North and South poles, research has shown that the clouds are particularly sensitive to changes in the atmosphere. Wind activity in the northern hemisphere appears to be influencing circulation about 20,900 kilometers (13,000 miles) away in the southern hemisphere.

While the clouds are seen primarily at higher latitudes, they have been sighted, according to NASA, as far south as Colorado and Virginia.

The best time to look for them is between late May and late August, and about 30-60 minutes after sunset, when the Sun is 6-16 degrees below the horizon.

These ‘shining’ clouds have a faintly bluish tint, can appear as parallel bands with diffuse edges, or might be seen as blue and white “tendrils spreading across the sky.”