Noctilucent clouds have been increasing in area, timing and intensity for the last decade. Given levels of CH4 being observed high in the Arctic atmosphere, I expect the trend to continue. What effect they will have on climate change is still under study.
Below is excerpts from the recent phys.org article on their early appearance in 2013.
Noctilucent clouds get an early startJun 10, 2013 by Tony Phillips
"News flash: This year, NLCs are getting an early start. NASA's AIM spacecraft, which is orbiting Earth on a mission to study noctilucent clouds, started seeing them on May 13th.
"The 2013 season is remarkable because it started in the northern hemisphere a week earlier than any other season that AIM has observed," reports Cora Randall of the Laboratory for Atmospheric and Space Physics at the University of Colorado. "This is quite possibly earlier than ever before."
The early start is extra-puzzling because of the solar cycle. Researchers have long known that NLCs tend to peak during solar minimum and bottom-out during solar maximum—a fairly strong anti-correlation. "If anything, we would have expected a later start this year because the solar cycle is near its maximum," Randall says. "So much for expectations."....
When AIM was launched in 2007, the underlying cause of NLCs was still unknown. Researchers knew they formed 83 km above Earth's surface where the atmosphere meets the vacuum of space—but that's about all. AIM quickly filled in the gaps.....
One of the greenhouse gases that has become more abundant in Earth's atmosphere since the 19th century is methane. "When methane makes its way into the upper atmosphere, it is oxidized by a complex series of reactions to form water vapor," says Russell. "This extra water vapor is then available to grow ice crystals for NLCs."
The early start of the 2013 season appears to be caused by a change in atmospheric "teleconnections."
"Half-a-world away from where the northern NLCs are forming, strong winds in the southern stratosphere are altering global circulation patterns," explains Randall. "This year more water vapor is being pushed into the high atmosphere where NLCs love to form, and the air there is getting colder."
"All of this has come as an interesting surprise for us," notes Russell. "When we launched AIM, our interest was in the clouds themselves. But now NLCs 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."
Read more at:
http://phys.org/news/2013-06-noctilucent-clouds-early.html#jCp
