Hello All!   
      
   Meteor Smoke Makes Strange Clouds    
      
   August 7, 2012:  Anyone who's ever seen a noctilucent cloud or "NLC" would   
   agree: They look alien.  The electric-blue ripples and pale tendrils of NLCs   
   reaching across the night sky resemble something from another world.    
      
   Researchers say that's not far off.  A key ingredient for the mysterious   
   clouds comes from outer space.    
      
   "We've detected bits of 'meteor smoke' imbedded in noctilucent clouds,"   
   reports James Russell of Hampton University, principal investigator of NASA's   
   AIM mission to study the phenomenon.  "This discovery supports the theory that   
   meteor dust is the nucleating agent around which NLCs form."    
      
   http://www.youtube.com/watch?v=Qzs9ZOsjF-c   
      
   A new ScienceCast video explains how "meteor smoke" seeds noctilucent clouds.   
   Play it   
      
   Noctilucent clouds are a mystery dating back to the late 19th century.    
   Northern sky watchers first noticed them in 1885 about two years after the   
   eruption of Krakatoa. Ash from the Indonesian volcano caused such splendid   
   sunsets that evening sky watching became a worldwide past time. One observer   
   in particular, a German named T.W. Backhouse who is often credited with the   
   discovery of NLCs, noticed something odd. He stayed outside longer than most   
   people, long enough for the twilight to fully darken, and on some nights he   
   saw wispy filaments glowing electric blue against the black sky. Scientists of   
   the day figured they were some manifestation of volcanic dust.    
      
   Eventually Krakatoa's ash settled and the sunsets faded, but strangely the   
   noctilucent clouds didn't go away. They're still present today, stronger than   
   ever.  Researchers aren't sure what role Krakatoa's ash played in those early   
   sightings.  One thing is clear, however:  The dust behind the clouds we see   
   now is space dust.    
      
   Mark Hervig of the company GATS, Inc, led the team that found the   
   extraterrestrial connection.    
      
   "Using AIM's Solar Occultation for Ice Experiment (SOFIE), we found that about   
   3% of each ice crystal in a noctilucent cloud is meteoritic," says Hervig.    
      
   The inner solar system is littered with meteoroids of all shapes and   
   sizes--from asteroid-sized chunks of rock to microscopic specks of dust.    
   Every day Earth scoops up tons of the material, mostly the small stuff. When   
   meteoroids hit our atmosphere and burn up, they leave behind a haze of tiny   
   particles suspended 70 km to 100 km above Earth's surface.    
      
   It's no coincidence that NLCs form 83 km high, squarely inside the meteor   
   smoke zone.    
      
   http://www.nasa.gov/images/content/662919main_ISS031-E-116058_lrg_full.jpg   
      
   Astronauts on board the ISS took this picture of noctilucent clouds near the   
   top of Earth's atmosphere on July 13, 2012. Larger image   
   Specks of meteor smoke act as gathering points where water molecules can   
   assemble themselves into ice crystals.  The process is called "nucleation."    
      
   Nucleation happens all the time in the lower atmosphere. In ordinary clouds,   
   airborne specks of dust and even living microbes can serve as nucleation   
   sites.  Tiny ice crystals, drops of water, and snowflakes grow around these   
   particles, falling to Earth if and when they become heavy enough.    
      
   Nucleating agents are especially important in the ethereal realm of NLCs.  The   
   clouds form at the edge of space where the air pressure is little more than   
   vacuum.  The odds of two water molecules meeting is slim, and of sticking   
   together slimmer still.     
      
   Meteor smoke helps beat the odds.  According AIM data, ice crystals can grow   
   around meteoritic dust to sizes ranging from 20 to 70 nanometers.  For   
   comparison, cirrus clouds in the lower atmosphere where water is abundant   
   contain crystals 10 to 100 times larger.    
      
   The small size of the ice crystals explains the clouds' blue color.  Small   
   particles tend to scatter short wavelengths of light (blue) more strongly than   
   long wavelengths (red).  So when a beam of sunlight hits an NLC, blue is the   
   color that gets scattered down to Earth.    
      
   Meteor smoke explains much about NLCs, but a key mystery remains: Why are the   
   clouds brightening and spreading?    
      
   In the 19th century, NLCs were confined to high latitudes-places like Canada   
   and Scandinavia.  In recent times, however, they have been spotted as far   
   south as Colorado, Utah and Nebraska. The reason, Russell believes, is climate   
   change.  One of the greenhouse gases that has become more abundant in Earth's   
   atmosphere since the 19th century is methane.  It comes from landfills,   
   natural gas and petroleum systems, agricultural activities, and coal mining.    
      
   It turns out that methane boosts NLCs.    
      
   http://science.nasa.gov/media/medialibrary/2012/08/07/methane_strip.jpg   
      
   A graphic prepared by Prof. James Russell of Hampton University shows how   
   methane, a greenhouse gas, boosts the abundance of water at the top of Earth's   
   atmosphere. This water freezes around "meteor smoke" to form icy noctilucent   
   clouds.    
      
   Russell explains: "When methane makes its way into the upper atmosphere, it is   
   oxidized by a complex series of reactions to form water vapor.  This extra   
   water vapor is then available to grow ice crystals for NLCs."    
      
   If this idea is correct, noctilucent clouds are a sort of "canary in a coal   
   mine" for one of the most important greenhouse gases.    
      
   And that, says Russell, is a great reason to study them.  "Noctilucent clouds   
   might look alien, but they're telling us something very important about our   
   own planet."    
      
      
   Author: Dr. Tony Phillips| Production editor: Dr. Tony Phillips | Credit:   
   Science@NASA   
      
   More Information    
    AIM (Aeronomy of Ice in the Mesosphere) -- mission home page    
      
   Strange Clouds -- Science@NASA    
      
   Realtime Noctilucent Cloud Photo Gallery -- spaceweather.com    
      
   NLC Observing tips: Look west 30 to 60 minutes after sunset when the Sun has   
   dipped 6ø to 16ø below the horizon. If you see luminous blue-white tendrils   
   spreading across the sky, you've probably spotted a noctilucent cloud.   
   Although noctilucent clouds appear most often at arctic latitudes, they have   
   been sighted in recent years as far south as Colorado, Utah and Nebraska. NLCs   
   are seasonal, appearing most often in late spring and summer. In the northern   
   hemisphere, the best time to look would be between mid-May and the end of   
   August.    
      
      
   Regards,   
      
   Roger    
   --- timEd/386 1.10.y2k+   
    * Origin: NCS BBS - Houma, LA - (1:3828/7)