[HoustonHam] From BBC News: Sun's 'quiet period' explained

[Chris Boone]

Sun's 'quiet period' explained

By Howard Falcon-Lang Science reporter 

 

The Sun's conveyor transports  plasma across its surface to the pole, where
it sinks before rising at the  equator Solar physicists may have discovered
why the Sun recently experienced a prolonged period of weak activity. 

The most recent so-called "solar minimum" occurred in December 2008.  

Its drawn-out nature extended the total length of the last solar cycle - the
repeating cycle of the Sun's activity - to 12.6 years, making it the longest
in  almost 200 years.  During a solar minimum the Sun is less active,
producing fewer sunspots and  flares. The new research suggests that the
longer-than-expected period of weak activity may have been linked to changes
in the way a hot soup of charged particles called plasma circulated in the
Sun.  

 

The study, conducted by Dr Mausumi Dikpati of the National Center for
Atmospheric Research in Colorado and her US colleagues, is published in the
journal Geophysical Research Letters. The Sun's activity strengthens and
weakens on a cycle that typically lasts 10.7 years. Since accurate records
began in 1755, there have been 24 such solar  cycles.  The 23rd cycle, which
ended in December 2008, was both longer than average and had the smallest
number of sunspots for a century. Sunspots are areas of  intense magnetic
activity that are visible as dark spots on the star's surface. Currents of
fire The new research suggests that one reason for the prolonged period of
weak activity could be changes in the Sun's "conveyor belt". 

 

Similar to the Earth's ocean currents, the Sun's conveyor transports plasma
across its surface to the pole. Here, the plasma sinks into the heart of the
Sun  before rising again at the equator. 

During the 23rd cycle, these currents of fire extended all the way to the
poles, while in earlier cycles they only extended about two thirds of the
way. 

Dr Roger Ulrich of the University of California, Los Angeles, a co-author of
the study, said the findings highlighted the importance of our monitoring of
the  Sun. 

 

The research team used sophisticated computer simulations to show how
changes  in the conveyor might have affected cycle duration. They found that
the increased length of the conveyor and its slower rate of return flow
explained  the prolonged 23rd cycle. 

However, Dr David Hathaway, a solar physicist from NASA's Marshall Space
Flight Center in Alabama, who was not involved in the latest study, argued
that  it was the speed and not the extent of the conveyor that was of real
importance.  

The conveyor has been running at record high-speeds for over five years. Dr
Hathaway said: "I believe this could explain the unusually deep solar
minimum."