Researchers Crack the Mystery of the Missing Sunspots   
       
   March 2, 2011: In 2008-2009, sunspots almost completely disappeared for two   
   years. Solar activity dropped to hundred-year lows; Earth's upper atmosphere   
   cooled and collapsed; the sun's magnetic field weakened, allowing cosmic rays   
   to penetrate the Solar System in record numbers. It was a big event, and solar   
   physicists openly wondered, where have all the sunspots gone?   
       
   Now they know. An answer is being published in the March 3rd edition of Nature.   
   [...]   
   In this artistic cutaway view of the sun, the Great Conveyor Belt appears as a   
   set of black loops connecting the stellar surface to the interior. Credit:   
   Andr‚s Mu¤oz-Jaramillo of the Harvard CfA. "Plasma currents deep inside the   
   sun interfered with the formation of sunspots and prolonged solar minimum,"   
   says lead author Dibyendu Nandi of the Indian Institute of Science Education   
   and Research in Kolkata. "Our conclusions are based on a new computer model of   
   the sun's interior."   
       
   For years, solar physicists have recognized the importance of the sun's "Great   
   Conveyor Belt." A vast system of plasma currents called `meridional flows'   
   (akin to ocean currents on Earth)  travel along the sun's surface, plunge   
   inward around the poles, and pop up again near the sun's equator. These   
   looping currents play a key role in the 11-year solar cycle.  When sunspots   
   begin to decay, surface currents sweep up their magnetic remains and pull them   
   down inside the star; 300,000 km below the surface, the sun's magnetic dynamo   
   amplifies the decaying magnetic fields.  Re-animated sunspots become buoyant   
   and bob up to the surface like a cork in water-voila!  A new solar cycle is   
   born.   
       
   For the first time, Nandi's team believes they have developed a computer model   
   that gets the physics right for all three aspects of this process--the   
   magnetic dynamo, the conveyor belt, and the buoyant evolution of sunspot   
   magnetic fields.   
       
   "According to our model, the trouble with sunspots actually began in back in   
   the late 1990s during the upswing of Solar Cycle 23," says co-author Andr‚s   
   Mu¤oz-Jaramillo of the Harvard-Smithsonian Center for Astrophysics. "At that   
   time, the conveyor belt sped up."   
       
   The fast-moving belt rapidly dragged sunspot corpses down to sun's inner   
   dynamo for amplification. At first glance, this might seem to boost sunspot   
   production, but no. When the remains of old sunspots reached the dynamo, they   
   rode the belt through the amplification zone too hastily for full   
   re-animation.  Sunspot production was stunted.   
   [...]   
   Sunspot cycles over the last century. The blue curve shows the cyclic   
   variation in the number of sunspots. Red bars show the cumulative number of   
   sunspot-less days. The minimum of sunspot cycle 23 was the longest in the   
   space age with the largest number of spotless days. Credit: Dibyendu Nandi et   
   al.   
   Later, in the 2000s, according to the model, the Conveyor Belt slowed down   
   again, allowing magnetic fields to spend more time in the amplification zone,   
   but the damage was already done.  New sunspots were in short supply.  Adding   
   insult to injury, the slow moving belt did little to assist re-animated   
   sunspots on their journey back to the surface, delaying the onset of Solar   
   Cycle 24.   
       
   "The stage was set for the deepest solar minimum in a century," says co-author   
   Petrus Martens of the Montana State University Department of Physics.   
       
   Colleagues and supporters of the team are calling the new model a significant   
   advance.   
       
   "Understanding and predicting solar minimum is something we've never been able   
   to do before---and it turns out to be very important," says Lika Guhathakurta   
   of NASA's Heliophysics Division in Washington, DC.   
   [...]   
   Three years ago on March 2, 2008, the face of the sun was featureless--no   
   sunspots. Credit: SOHO/MDI While Solar Max is relatively brief, lasting a few   
   years punctuated by episodes of violent flaring, over and done in days, Solar   
   Minimum can grind on for many years. The famous Maunder Minimum of the 17th   
   century lasted 70 years and coincided with the deepest part of Europe's Little   
   Ice Age. Researchers are still struggling to understand the connection.   
       
   One thing is clear: During long minima, strange things happen. In 2008-2009,   
   the sun's global magnetic field weakened and the solar wind subsided.  Cosmic   
   rays normally held at bay by the sun's windy magnetism surged into the inner   
   solar system.  During the deepest solar minimum in a century, ironically,   
   space became a more dangerous place to travel.  At the same time, the heating   
   action of UV rays normally provided by sunspots was absent, so Earth's upper   
   atmosphere began to cool and collapse.  Space junk stopped decaying as rapidly   
   as usual and started accumulating in Earth orbit.  And so on..   
       
   Nandi notes that their new computer model explained not only the absence of   
   sunspots but also the sun's weakened magnetic field in 08-09.  "It's   
   confirmation that we're on the right track."   
       
   Next step:  NASA's Solar Dynamics Observatory (SDO) can measure the motions of   
   the sun's conveyor belt-not just on the surface but deep inside, too. The   
   technique is called helioseismology; it reveals the sun's interior in much the   
   same way that an ultrasound works on a pregnant woman.  By plugging SDO's   
   high-quality data into the computer model, the researchers might be able to   
   predict how future solar minima will unfold.  SDO is just getting started,   
   however, so forecasts will have to wait.   
       
   Indeed, much work remains to be done, but, says Guhathakurta, "finally, we may   
   be cracking the mystery of the spotless sun."   
       
   Credits:  This research was funded by NASA's Living With a Star Program and   
   the Department of Science and Technology of the Government of India.   
       
       
   Author: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
       
   Spotless Sun: Blankest Year of tthe Space Age -- Science@NASA   
       
   Puzzling Collapse of Earth's Upper Atmosphere -- Science@NASA   
       
   Solar Wind Loses Power, Hits 50-year Low --- Science@NASA   
       
   Cosmic Rays Hit Space Age High --- Science@NASA   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.59   
    * Origin: NCS BBS (1:3828/7)