Skywatchers across the country enjoying outburst of rarely seen 'jaw-dropping' clouds
If you've happened to glance up at the sky about an hour after sunset or an hour before sunrise and noticed wispy, electric blue clouds on the horizon, you've managed to catch a rare sighting of noctilucent clouds, or NLCs.
Over the past few weeks, NLCs, also known as polar mesospheric clouds, have been spotted not just in northern regions, but in areas that have never had reported sightings before, including as far south as California.
"We're seeing more [NLCs] this year than any other time," said James Russell, principal investigator for NASA's Aeronomy of Ice in the Mesosphere (AIM) satellite that studies NLCs. "In fact, we've seen them at the lowest latitudes on record."
NLCs are the highest clouds in our atmosphere, at an altitude of roughly 80 kilometres.
While NLCs still aren't completely understood, researchers know that three things need to be present in order for them to form: an increase in water vapour, very cold temperatures and particles on which the water vapour can freeze.
The sun must also be at least six degrees below the horizon to illuminate the clouds.
Early this morning I saw from Joshua Tree a rare sight from this latitude, noctilucent clouds floating like pale windblown webs above the twilight. They are the highest of clouds, looming at the edge of space and shining with the blue-white color of unfiltered sunlight. pic.twitter.com/xdbf0HZi3x—@DDAVISSPACEART
The first recorded sighting of NLCs was in 1885, two years after the violent eruption of the Krakatoa volcano in Indonesia. At the time, many scientists believed that the two events were somehow linked. However, NLCs have continued to appear at the poles year after year.
Now scientists believe that perhaps dust from meteroid particles — tiny bits of space dust present in our atmosphere — could be the particles on which ice crystals form once the water vapour freezes.
But why are NLC sightings on the rise?
Scientists believe that what's changed is an increase in water vapour in the upper atmosphere.
"We know there is more water in lower latitudes than ever before in the time period we've been observing, over the last 12 years," Russell said.
While water vapour can act as a blanket, warming the Earth below, up in the higher atmosphere, closer to the coldness of space, the atmosphere radiates heat outward and cools.
And that might account for NLC sightings so far south.
There is also another factor that might be contributing to the phenomenon.
The sun goes through a cycle every 11 years, going from a period of high activity, with more sunspots and flares, for example, to one of lower activity. Even at its maximum, the sun hasn't been quite as active over the past few cycles and, at the moment, we're heading into the peak of lower activity, called a solar minimum.
When the sun isn't as active, it can cause the mesosphere, a region in our upper atmosphere, to cool down even more. Russell said there's a theory that perhaps the cooler temperatures and increased water vapour might be behind the increase in NLC activity.
No matter the reason behind the NLCs, people are enjoying the show.
Mike Noble, who is fortunate to live in Edmonton, where these displays are more easily seen, has been chasing them since 2012. He has spotted NLCs on more than 250 different nights — 50 of those in 2018 alone.
NLCs are typically spotted in the northern hemisphere between late May and August. Noble first spotted them this season on May 25, beating his previous early record of May 28 last year.
"The activity of noctilucent clouds this year has been much more," Noble said.
On some nights, Noble said, the initial presence of NLCs starts with almost a whisper — a slight glow against the evening twilight sky. Whereas other nights, "it can explode and it can get so bright."
Alister Ling, a retired meteorologist who also hails from Edmonton and is an NLC chaser, says he hopes one day to create a model that can forecast when NLCs might occur — something that's never been done successfully.
"Nothing of interest happens that high [in the atmosphere] that affects the day-to-day life for airplanes or people, so weather models don't have the need to go up that high."
For now, he is enjoying the incredible displays.
"One of the things that I love about observing noctilucent clouds with binoculars is a nice display that is jaw-dropping," he said. "The level of detail, the waves."
If you want to see them for yourself, look north about an hour after sunset or an hour before sunrise, and be sure you have a good view of the northern horizon.
While it can't be said for certain how long this particular outburst will last, Noble encourages people to enjoy the night sky.
"I want people to get out of their beds and look up," he said. "There are things to see at night."