Electric Blue Sunsets   
       
   Aug 16, 2016:  Northern summer is underway. It's time for picnics, hot dogs,   
   dips in the pool... and, oh yes, electric blue sunsets.   
       
   Just below the Arctic Circle, evening skies are filling with pale blue   
   ripples. They appear just after sunset or just before sunrise and are called   
   noctilucent clouds (NLCs). When viewed from space, the same atmospheric   
   phenomenon is referred to as polar mesospheric clouds (PMCs).   
       
   https://www.youtube.com/watch?v=EAVJrLRBRPY   
       
   Cora Randall, chair of the Department of Atmospheric and Oceanic Sciences at   
   the University of Colorado says, "The 2016 season for noctilucent clouds began   
   on May 24th when NASA's Aeronomy of Ice in the Mesosphere satellite (AIM)   
   spotted a puff of electric blue around the Arctic Circle."   
       
   NLCs are Earth's highest clouds. Seeded by meteoroids, they float at the edge   
   of space more than 50 miles above the planet's surface. The clouds are very   
   cold and filled with tiny ice crystals. Those tiny crystals do a good job of   
   scattering blue light from the rising or setting sun-hence their electric blue   
   color.   
       
   Noctilucent clouds appear during summer because, ironically, that is the only   
   time the upper atmosphere at high latitudes is cold enough to crystalize   
   molecules of water around specks of meteor dust. The role of meteor dust in   
   forming NLCs is one of many discoveries made by AIM, which NASA launched in   
   2007 to study the mysterious clouds.   
       
   James Russell, principal investigator for AIM at Hampton University says,   
   "These clouds continue to reveal intimate details about how the atmosphere   
   works. Each season yields new information."   
       
   The first recorded observations of noctilucent clouds were made in the 19th   
   century after the eruption of super-volcano Krakatoa. At the time, people   
   thought the clouds were caused by the eruption, but long after Krakatoa's ash   
   settled, the clouds remained. In those days, NLCs were a polar phenomenon   
   confined mainly to the Arctic. In recent years, they have intensified and   
   spread with sightings as far south as Colorado and Kansas.   
       
   The reason may be climate change on the edge of space.  A recent study by AIM   
   science team member Mark Hervig and colleagues published March 2016 in the   
   Journal of Geophysical Research confirms that the mesosphere, the atmospheric   
   layer where NLCs form, has gotten colder and moister in recent decades. Both   
   trends promote the formation of NLCs.   
       
   Their results are consistent with a simple model linking the clouds to two   
   greenhouse gases. First, carbon dioxide promotes NLCs by making the mesosphere   
   colder. While increasing carbon dioxide warms the surface of the Earth, those   
   same molecules cool the upper atmosphere - a yin-yang relationship long known   
   to climate scientists. Second, methane promotes the clouds by adding moisture   
   to the mesosphere because methane oxidizes into water as it rises in the   
   atmosphere.   
       
   Noctilucent clouds appear to be a telltale sign of important greenhouse   
   gases.  And that, says Russell, is a great reason to study them. "They may be   
   at the edge of space, but they're telling us something very important about   
   our own planet."   
       
   For more news from the edge of space, stay tuned to science.nasa.gov.   
       
       
   Regards,   
       
   Roger   
      
   --- DB 3.99 + W10 (1607)   
    * Origin: NCS BBS - Houma, LoUiSiAna (1:3828/7)