The sun has been feisty lately, spewing out superheated particles
as it nears a peak in its 11-year solar cycle. Earlier this month, it helped create two ethereal spectacles at the same time and place on Earth — a rare event that wasn't just improbably caught on film, but immortalized in a high-quality, time-lapse video for the entire Internet to see.
This twilight double feature co-stars aurora borealis
and noctilucent clouds
, also known as northern lights and night-shining clouds, respectively. Auroras occur when solar particles react with gases in Earth's atmosphere, producing vivid light displays at the edge of space. Noctilucent clouds are the planet's highest-altitude cloud type, forming up to 50 miles high as ice crystals cling to meteor smoke. Their elevation lets them reflect sunlight well past sunset, creating a ghostly blue glow when most clouds are shrouded in darkness.
Both the northern lights and noctilucent clouds are high-latitude phenomena, generally lingering around Arctic or sub-Arctic areas. Either one would be a once-in-a-lifetime sight for most people, so Winiarczyk was lucky to see — and film — both at once. On top of that, the same solar storm
activity that triggers auroras is normally associated with fewer noctilucent clouds, making a joint performance like this especially rare.
But 2013 isn't a typical year for noctilucent clouds. They usually appear in summer — when more water rises from the lower atmosphere to mix with smoky meteor trails — but they defied expectations this year with one of their earliest appearances on record.
"The 2013 season is remarkable because it started in the northern hemisphere a week earlier than any other season that AIM has observed," University of Colorado researcher Cora Randall said in a June statement from NASA
, referring to the Aeronomy of Ice in the Mesosphere satellite. "This is quite possibly earlier than ever before. If anything, we would have expected a later start this year because the solar cycle is near its maximum."
Beyond this year's early start, noctilucent clouds (NLCs) have also been venturing farther south lately, a trend some researchers link to climate change
. Long limited to the far north after their 19th-century debut, the blue wisps have shown up as far south as Colorado and Utah in recent years. This may be partly due to industrial emissions of greenhouse gases
like methane, which have skyrocketed since the first reported NLC sighting in 1885.
"When methane makes its way into the upper atmosphere, it is oxidized by a complex series of reactions to form water vapor," AIM investigator James Russell explains in the NASA statement. "This extra water vapor is then available to grow ice crystals for NLCs."
Other climate changes may also favor the spread of NLCs, from disrupted wind patterns to an expected cooling of the mesosphere
. "Half a world away from where the northern NLCs are forming, strong winds in the southern stratosphere are altering global circulation patterns," Randall says. "This year more water vapor is being pushed into the high atmosphere where NLCs love to form, and the air there is getting colder."
The AIM satellite was launched in 2007 to study NLCs, and its mission was recently extended for two years
, offering researchers more opportunities to demystify the clouds and their climate connections. In the meantime, sky watchers may have also more chances to see impressive twilight shows like the one above — in addition to the rise in NLCs, NASA scientists say the sun may be experiencing a "double-humped solar maximum
," meaning the higher odds of aurora displays could stretch into 2014.
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