Spacecraft Sees Solar Storm Engulf Earth   
       
   August 18, 2011: For the first time, a spacecraft far from Earth has turned   
   and watched a solar storm engulf our planet. The movie, released today during   
   a NASA press conference, has galvanized solar physicists, who say it could   
   lead to important advances in space weather forecasting.   
       
   "The movie sent chills down my spine," says Craig DeForest of the Southwest   
   Research Institute in Boulder, Colorado.  "It shows a CME swelling into an   
   enormous wall of plasma and then washing over the tiny blue speck of Earth   
   where we live.  I felt very small."   
       
   http://science.nasa.gov/media/medialibrary/2011/08/18/V5_Craig_Science_Gauge_   
   hlfspdH.264.mov   
       
   A wide-angle movie recorded by NASA's STEREO-A spacecraft shows a solar storm   
   traveling all the way from the sun to Earth and engulfing our planet. A 17 MB   
   Quicktime zoom adds perspective to the main 40 MB Quicktime movie.   
   CMEs are billion-ton clouds of solar plasma launched by the same explosions   
   that spark solar flares.   When they sweep past our planet, they can cause   
   auroras, radiation storms, and in extreme cases power outages.  Tracking these   
   clouds and predicting their arrival is an important part of space weather   
   forecasting.   
       
   "We have seen CMEs before, but never quite like this," says  Lika   
   Guhathakurta, program scientist for the STEREO mission at NASA headquarters.   
   "STEREO-A has given us a new view of solar storms."   
       
   STEREO-A is one of two spacecraft launched in 2006 to observe solar activity   
   from widely-spaced locations. At the time of the storm, STEREO-A was more than   
   65 million miles from Earth, giving it the "big picture" view other spacecraft   
   in Earth orbit have been missing.   
       
   When CMEs first leave the sun, they are bright and easy to see. Visibility is   
   quickly reduced, however, as the clouds expand into the void.  By the time a   
   typical CME crosses the orbit of Venus, it is a billion times fainter than the   
   surface of the full Moon, and more than a thousand times fainter than the   
   Milky Way.  CMEs that reach Earth are almost as gossamer as vacuum itself and   
   correspondingly transparent.   
       
   "Pulling these faint clouds out of the confusion of starlight and   
   interplanetary dust has been an enormous challenge," says DeForest.   
       
   Indeed, it took almost three years for his team to learn how to do it. Footage   
   of the storm released today was recorded back in December 2008, and they have   
   been working on it ever since.  Now that the technique has been perfected, it   
   can be applied on a regular basis without such a long delay.   
       
   Alysha Reinard of NOAA's Space Weather Prediction Center explains the benefits   
   for space weather forecasting:   
       
   "Until quite recently, spacecraft could see CMEs only when they were still   
   quite close to the sun. By calculating a CME's speed during this brief period,   
   we were able to estimate when it would reach Earth. After the first few hours,   
   however, the CME would leave this field of view and after that we were 'in the   
   dark' about its progress."   
       
   "The ability to track a cloud continuously from the Sun to Earth is a big   
   improvement," she continues.  "In the past, our very best predictions of CME   
   arrival times had uncertainties of plus or minus 4 hours," she continues. "The   
   kind of movies we've seen today could significantly reduce the error bars."   
       
   http://science.nasa.gov/media/medialibrary/2011/08/18/V4_Craig_Zoom.mov   
       
   This 17 MB Quicktime zoom adds perspective to the main 40 MB Quicktime movie   
   of the CME engulfing Earth. The movies pinpoint not only the arrival time of   
   the CME, but also its mass.  From the brightness of the cloud, researchers can   
   calculate the gas density with impressive precision.  Their results for the   
   Dec. 2008 event agreed with actual in situ measurements at the few percent   
   level.  When this technique is applied to future storms, forecasters will be   
   able to estimate its impact with greater confidence.   
       
   At the press conference, DeForest pointed out some of the movie's highlights:   
   When the CME first left the sun, it was cavernous, with walls of magnetism   
   encircling a cloud of low-density gas. As the CME crossed the Sun-Earth   
   divide, however, its shape changed. The CME "snow-plowed" through the solar   
   wind, scooping up material to form a towering wall of plasma. By the time the   
   CME reached Earth, its forward wall was sagging inward under the weight of   
   accumulated gas.   
       
   The kind of magnetic transformations revealed by the movie deeply impressed   
   Guhathakurta:  "I have always thought that in heliophysics understanding the   
   magnetic field is equivalent to the `dark energy' problem of astrophysics.   
   Often, we cannot see the magnetic field, yet it orchestrates almost   
   everything.   These images from STEREO give us a real sense of what the   
   underlying magnetic field is doing."   
       
   All of the speakers at today's press event stressed that the images go beyond   
   the understanding of a single event.  The inner physics of CMEs have been laid   
   bare for the first time-a development that will profoundly shape theoretical   
   models and computer-generated forecasts of CMEs for many years to come.   
       
   "This is what the STEREO mission was launched to do," concludes Guhathakurta,   
   "and it is terrific to see it live up to that promise."   
       
       
   Author: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
   STEREO -- mission home page   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.64   
    * Origin: NCS BBS (1:3828/7)