Every year, for a period of between five to 10 days, the night skies over Antarctica and the Arctic Circle are visited by an unusual phenomenon known as noctilucent clouds (NLCs) or polar mesospheric clouds (PMCs). Residing at an altitude between 47 to 53 miles, these electric-blue clouds are the highest in Earth's atmosphere and can only be observed well after the sun has dipped below the horizon at twilight.
When NASA launched a balloon from Sweden across the Arctic towards Canada to observe the clouds in July 2018, that was just the beginning. The balloon captured 6 million high-resolution images over the course of five days, which the video above shows.
"This is the first time we’ve been able to visualize the flow of energy from larger gravity waves to smaller flow instabilities and turbulence in the upper atmosphere," said Dave Fritts, principal investigator of the PMC Turbo mission at Global Atmospheric Technologies and Sciences in Boulder, Colorado, in a NASA press release. "At these altitudes you can literally see the gravity waves breaking — like ocean waves on the beach — and cascading to turbulence."
What are noctilucent or night clouds?
According to NASA, night clouds are a relatively new phenomenon, with the first observations occurring a couple years after the eruption of Krakatoa in 1883 sent tons of volcanic ash high into the atmosphere. They increased again after the Tunguska meteor event over Siberia in 1908. In 2007, NASA launched the AIM satellite (Aeronomy of Ice in the Mesosphere) to study noctilucent clouds and learn more about the conditions that favor their formation. That mission continues today, with images like the one below coming in if the conditions are right.
The AIM spacecraft spied these noctilucent clouds over the North Pole in June 2007. (Photo: HU/VT/CU LASP/NASA)
"AIM and other research has shown that in order for the clouds to form, three things are needed: very cold temperatures, water vapor and meteoric dust," James Russell, an atmospheric and planetary scientist at Hampton University, said in a NASA article. "The meteoric dust provides sites that the water vapor can cling to until the cold temperatures cause water ice to form."
The Krakatoa event likely "seeded" the upper atmosphere with dust, allowing noctilucent clouds to be seen over more populated areas. In its most recent observations, however, NASA is reporting that the blue cloud formations are not only starting earlier than normal, but also spreading beyond the polar regions.
Not a pretty reason behind the pretty display
Researchers believe the beautiful twilight displays, observed as far south as Colorado and Utah, could be due to an increased abundance of methane in the upper atmosphere.
"When methane makes its way into the upper atmosphere, it is oxidized by a complex series of reactions to form water vapor," Russell added. "This extra water vapor is then available to grow ice crystals for NLCs."
Because methane is a heat-trapping greenhouse gas that's roughly 30 times more potent than carbon dioxide, its theorized that noctilucent clouds are a canary in the climate change coal mine. In fact, a study in Geophysical Research Letters backed up that premise, saying that increased water vapor in Earth's atmosphere due to human activities is making shimmering high-altitude clouds more visible.
Editor's note: This article has been updated since it was originally published in December 2016.