[EIDXA] Forecast of Next Sunspot Cycle

[Tom Hise]

March 6, 2006

Scientists Issue Unprecedented Forecast of Next Sunspot Cycle

http://www.physorg.com/news11434.html

BOULDER -- The next sunspot cycle will be 30-50% stronger than the last 
one and begin as much as a year late, according to a breakthrough forecast 
using a computer model of solar dynamics developed by scientists at the 
National Center for Atmospheric Research (NCAR). Predicting the Sun's 
cycles accurately, years in advance, will help societies plan for active 
bouts of solar storms, which can slow satellite orbits, disrupt 
communications, and bring down power systems.

The scientists have confidence in the forecast because, in a series of 
test runs, the newly developed model simulated the strength of the past 
eight solar cycles with more than 98% accuracy. The forecasts are 
generated, in part, by tracking the subsurface movements of the sunspot 
remnants of the previous two solar cycles. The team is publishing its 
forecast in the current issue of Geophysical Research Letters.

"Our model has demonstrated the necessary skill to be used as a 
forecasting tool," says NCAR scientist Mausumi Dikpati, the leader of the 
forecast team at NCAR's High Altitude Observatory that also includes Peter 
Gilman and Giuliana de Toma.

Understanding the cycles

The Sun goes through approximately 11-year cycles, from peak storm 
activity to quiet and back again. Solar scientists have tracked them for 
some time without being able to predict their relative intensity or 
timing.

Forecasting the cycle may help society anticipate solar storms, which can 
disrupt communications and power systems and affect the orbits of 
satellites. The storms are linked to twisted magnetic fields in the Sun 
that suddenly snap and release tremendous amounts of energy. They tend to 
occur near dark regions of concentrated magnetic fields, known as 
sunspots.

The NCAR team's computer model, known as the Predictive Flux-transport 
Dynamo Model, draws on research by NCAR scientists indicating that the 
evolution of sunspots is caused by a current of plasma, or electrified 
gas, that circulates between the Sun's equator and its poles over a period 
of 17 to 22 years. This current acts like a conveyor belt of sunspots.

The sunspot process begins with tightly concentrated magnetic field lines 
in the solar convection zone (the outermost layer of the Sun's interior). 
The field lines rise to the surface at low latitudes and form bipolar 
sunspots, which are regions of concentrated magnetic fields. When these 
sunspots decay, they imprint the moving plasma with a type of magnetic 
signature. As the plasma nears the poles, it sinks about 200,000 
kilometers (124,000 miles) back into the convection zone and starts 
returning toward the equator at a speed of about one meter (three feet) 
per second or slower. The increasingly concentrated fields become 
stretched and twisted by the internal rotation of the Sun as they near the 
equator, gradually becoming less stable than the surrounding plasma. This 
eventually causes coiled-up magnetic field lines to rise up, tear through 
the Sun's surface, and create new sunspots.

The subsurface plasma flow used in the model has been verified with the 
relatively new technique of helioseismology, based on observations from 
both NSF- and NASA-supported instruments. This technique tracks sound 
waves reverberating inside the Sun to reveal details about the interior, 
much as a doctor might use an ultrasound to see inside a patient.

Predicting Cycles 24 and 25

The Predictive Flux-transport Dynamo Model is enabling NCAR scientists to 
predict that the next solar cycle, known as Cycle 24, will produce 
sunspots across an area slightly larger than 2.5% of the visible surface 
of the Sun. The scientists expect the cycle to begin in late 2007 or early 
2008, which is about 6 to 12 months later than a cycle would normally 
start. Cycle 24 is likely to reach its peak about 2012.

By analyzing recent solar cycles, the scientists also hope to forecast 
sunspot activity two solar cycles, or 22 years, into the future. The NCAR 
team is planning in the next year to issue a forecast of Cycle 25, which 
will peak in the early 2020s.

"This is a significant breakthrough with important applications, 
especially for satellite-dependent sectors of society," explains NCAR 
scientist Peter Gilman.

The NCAR team received funding from the National Science Foundation and 
NASA¹s Living with a Star program.

The National Center for Atmospheric Research and UCAR Office of Programs 
are operated by University Corporation for Atmospheric Research under the 
sponsorship of the National Science Foundation and other agencies.

Related sites on the World Wide Web:

* NCAR's High Altitude Observatory
  http://www.hao.ucar.edu/
* Geophysical Research Letters
  http://www.agu.org/journals/gl/