Noctilucent clouds seen in London on Sunday. (Phil Harper via/

Sunday night featured sublime weather in London. The air was dry, temperatures fell into the 60s, and high pressure brought a pleasant evening. But shortly after sunset, the sky lit up with shimmering, electric-blue curtains. Then the same thing happened early this week over Canada and the Pacific Northwest, including Portland, Ore.

The culprit? Noctilucent clouds, unpredictable yet spectacular apparitions perched on the edge of space. Seeded by meteor smoke, they form mostly at high latitudes near the north and south pole. But emerging research suggests they may be venturing closer to the equator, a potential byproduct of climate change as changes unfold in the upper atmosphere.

This month, they have been seen and photographed in Washington, Wyoming, Oregon, Idaho, Minnesota, Canada and in several countries in Europe.

“Even the bright lights of the London Eye on the river Thames couldn’t drown out the display,” Phil Halper told, where he posted photographs. “These were the most spectacular NLCs [noctilucent clouds] I’ve ever seen.”

Halper photographed the magnificent clouds at several of London’s landmarks, racing around the city to document the spectacle, falling off his bike and landing in the hospital in the process. But “it was well worth it,” he told

The alien-like clouds then landed in Oregon early Tuesday. Broadcast meteorologist Jeff Forgeron, out of Portland, called the display “incredible.”

What are these shimmering blue space clouds?

Noctilucent clouds remain illuminated after dark because of their extreme altitude — a whopping 50 miles above the Earth’s surface. That permits them to capture the lingering rays of a waning sun that has already set at the surface, the ghostly ice clouds remaining emblazoned for hours against the deep azure of twilight.

Noctilucent clouds were visible over Portland, Ore., Tuesday morning. (Andrew Morgan/

The process of generating a noctilucent cloud begins when thin wisps of meteor smoke spread out in the mesosphere after their parent objects burn up. The mesosphere is the third layer of the atmosphere above both the stratosphere and the troposphere, the closest layer to the ground where most of our weather occurs. The northern lights occur even higher up in the thermosphere.

Noctilucent clouds shine after sunset near Okotoks, Alberta, on Tuesday. (Harlan Thomas/

Most of the time, the meteor smoke disintegrates or gradually filters lower into the atmosphere. But on occasion, the tiny particulates can provide a seed for moisture to collect upon. And a noctilucent cloud is born.

A delicate process

It sounds like a straightforward process, but getting all the ingredients to overlap is a rare feat. Temperatures at that height in the atmosphere can approach minus-190 degrees. And the colder the air gets, the less water it can contain.

Noctilucent clouds shine over Richland, Wash., on Tuesday (Scott Butner/

Frigid temperatures are instrumental in spawning noctilucent clouds. And oddly enough, temperatures in the upper mesosphere are coldest in the summer. It’s counterintuitive, but it’s due to an atmospheric circulation that forces air upward in the summertime, where it expands and cools. Sinking air from the thermosphere above in the wintertime has the opposite effect and warms.

According to, this June has already featured record cold temperatures in the mesosphere, with a greater presence of water. That has made it ripe for an outbreak of noctilucent clouds.

Last year, a June episode of noctilucent clouds was visible from at least 10 states across the northern United States, including California and Oklahoma.

How climate change may result in more displays of noctilucent clouds

More people may get in on the show in the years to come, though. Atmospheric scientists have linked greenhouse gas emissions to a process that contributes to forming noctilucent clouds.

In addition to the more widely-discussed carbon dioxide, human activity releases methane into the atmosphere. If it makes it high enough into the atmosphere, it can become oxidized — and, through a complex series of reactions, create water vapor. That extra water vapor then becomes available to create noctilucent clouds.

Sightings of noctilucent clouds have been on the rise for decades, with their increasing frequency and areal coverage the subject of numerous research efforts.

If you live across the northern United States or Canada, you may be able to try your hand at spotting some. Just look west about an hour after sunset.

If you spot some neon blue-looking clouds, you may have caught yourself a noctilucent cloud some 250,000 feet up. And masked in its beauty lurks a potentially more subtle climate warning.

Jason Samenow contributed to this report.

Correction: The description of how a noctilucent cloud is born was amended as it does not involve freezing of supercooled droplets as originally stated.