Diaphanous, ephemeral, the clouds of summer sunsets that usually arrive in June are early this year, and some researchers believe that may be fueled by climate change.
"The 2013 season is remarkable because it started in the northern hemisphere a week earlier than any other season that AIM has observed," said Cora Randall of the Laboratory for Atmospheric and Space Physics at the University of Colorado, referring to NASA’s satellite mission Aeronomy of Ice in the Mesosphere (AIM). "This is quite possibly earlier than ever before."
Hanging 53 miles above Mother Earth, these so-called night-shining clouds undulate above the western horizon, poised “at the edge of space itself, circling the north and south pole regions,” NASA said in a 2012 description. They are formed by water droplets that crystalize around what NASA calls “meteor smoke.”
"It turns out that meteoroids play an important role in the formation of NLCs," said Hampton University Professor James Russell, AIM’s main investigator. "Specks of debris from disintegrating meteors act as nucleating points where water molecules can gather and crystallize."
What the early season tells scientists is something that the keepers of traditional knowledge have known for eons: that everything is interconnected. The early start of the 2013 season appears to be caused by a change in atmospheric ‘teleconnections,’ ” is how NASA put it.
“Half-a-world away from where the northern [noctilucent clouds] are forming, strong winds in the southern stratosphere are altering global circulation patterns,” Randall said in the statement. "This year more water vapor is being pushed into the high atmosphere where [noctilucent clouds] love to form, and the air there is getting colder."
That’s where climate change comes in.
Whereas they used to stick to extreme latitudes, over the past few years the clouds’ range has been expanding. Nowadays they are often seen as far south as Colorado and Virginia. This is thought to be partly because of a preponderance of the greenhouse gas methane, which gets oxidized in the upper atmosphere, forming water vapor. That in turn grows the requisite ice crystals for the cloud formation.
"All of this has come as an interesting surprise for us," said Russell. "When we launched AIM, our interest was in the clouds themselves. But now [clouds] are teaching us about connections between different layers of the atmosphere that operate over great distances. Our ability to study these connections will surely lead to new understanding about how our atmosphere works."
The viewing season is not very long, so NASA suggests that eyes be trained skyward just after sunset for a glimpse of these hauntingly beautiful, electric-blue tendrils.