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On July 15th, a wave of intense noctilucent clouds (NLCs) descended over the continental United States. "They were so bright, I would have assumed the dawn was imminent, only it was an hour and a half before sunrise!" says Eve Wills, who sends this picture from Dillon, Montana.
Similar reports have poured in from Colorado, Oregon, Washington, Nebraska, Idaho, the Dakotas and northern California. These sightings are significant because they come from places so far south. When noctilucent clouds first appeared in the late 19th century, they were confined to latitudes above 50o N (usually far above). The latitude of last night's Colorado sighting is only 39° N. No one knows why NLCs are expanding their range; it's one of many unanswered questions about the mysterious clouds.
They are the highest clouds in the Earth's atmosphere, located in the mesosphere at altitudes of around 76 to 85 kilometers (47 to 53 mi). They are normally too faint to be seen, and are visible only when illuminated by sunlight from below the horizon while the lower layers of the atmosphere are in the Earth's shadow. Noctilucent clouds are not fully understood and are a recently discovered meteorological phenomenon; there is no evidence that they were observed before 1885.
Noctilucent clouds almost always surge during years of solar minimum such as 2009. No one fully understands the link, but here is a popular idea: Low solar activity allows the upper atmosphere to cool, promoting the formation of tiny ice crystals that make up noctilucent clouds.
Originally posted by sickofitall2012
reply to post by nydsdan
Yeah, what puzzles me is that if the atmosphere is so much colder, how does this play into the so-called global warming ?
The clouds were first seen above polar regions in 1885, suggesting they may have been caused by the eruption of Krakatoa two years before. But in recent years the clouds have spread to latitudes as low as 40°, while also growing in number and getting brighter. The reason for the clouds' spread is unclear, but some suspect it could be due to an increase in greenhouse gases. That's because the gases actually cause Earth's upper atmosphere to cool, and the clouds need cold temperatures to form.
Although the average number of noctilucent clouds has been increasing in recent decades, their abundance also seems to rise and fall with the sun's 11-year cycle of activity. The clouds thrive when the sun is quiet and spews less ultraviolet radiation, which can destroy water needed to form the clouds and can keep temperatures too high for ice particles to form.
Because the sun has been abnormally quiet in recent years, noctilucent clouds could be especially bright and numerous this summer in the Northern hemisphere. "We expect this year to be a bigger year because of lower solar activity," says Scott Bailey of Virginia Tech in Blacksburg, VA and a lead scientist for NASA's Aeronomy of Ice in the Mesosphere (AIM) spacecraft, which launched in 2007 to study the clouds. The clouds may be about twice as abundant this year as they are when the sun is at the peak of its activity, he says.
The Aeronomy of Ice in the Mesosphere (AIM) satellite mission is exploring Polar Mesospheric Clouds (PMCs), also called noctilucent clouds, to find out why they form and why they are changing.
The AIM mission has been extended by NASA through the end of FY12. During this time the instruments will monitor noctilucent clouds to better understand their variability and possible connection to climate change. Individual instrument data collection status, as well as spacecraft and instrument health, will be monitored throughout the life of the mission and reported periodically on this website.
On June 11, 2007 the cameras on the AIM satellite returned some of the first data documenting noctilucent clouds over the Arctic regions of Europe and North America. This new data reveals the global extent and structure of these mysterious clouds, to a degree that was previously unattainable. White and light blue represent noctilucent cloud structures. Black indicates areas where no data is available. Credit: Cloud Imaging and Particle Size Experiment data processing team at the University of Colorado Laboratory for Atmospheric and Space Physics
Originally posted by Aggie Man
When I was a child my grandfather used to call those clouds "mares tales". in the winter time it was seen by my grandfather as a precursor for snow/ice storms.