(Araucaria) Fw: Declining sunspot magnetic flux density

[PY2ZX]

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Flávio PY2ZX
==================

Sep 16 10:15AM -0400

An interesting article from ScienceNOW.

http://news.sciencemag.org/sciencenow/2010/09/say-goodbye-to-sunspots.html

*****
Say Goodbye to Sunspots?
by Phil Berardelli, 14 September 2010

Scientists studying sunspots for the past 2 decades have concluded that the
magnetic field that triggers their formation has been steadily 
declining. If the
current trend continues, by 2016 the sun's face may become spotless and 
remain
that way for decades---a phenomenon that in the 17th century coincided 
with a
prolonged period of cooling on Earth. ...

The last solar minimum should have ended last year, but something 
peculiar has
been happening. Although solar minimums normally last about 16 months, the
current one has stretched over 26 months---the longest in a century. One 
reason,
according to a paper submitted to the International Astronomical Union 
Symposium
No. 273, an online colloquium, is that the magnetic field strength of 
sunspots
appears to be waning.

Since 1990, solar astronomers Matthew Penn and William Livingston of the
National Solar Observatory in Tucson, Arizona, have been studying the 
magnetic
strength of sunspots using a measurement called Zeeman splitting. Named 
after
the Dutch physicist who discovered it, the splitting is the distance that
appears between a pair of lines in a spectrograph of the light given off 
by iron
atoms in the sun's atmosphere. The wider the splitting, the greater the
intensity of the magnetic field that created it. After examining the Zeeman
splitting of 1500 sunspots, Penn and Livingston conclude that the average
magnetic field strength of sunspots has declined from about 2700 
gauss---the
average strength of Earth's field is less than 1 gauss---to about 2000 
gauss. The
reasons for the decrease are not clearly understood, but if the trend 
continues,
sunspot field strength will drop to 1500 gauss by as early as 2016. 
Because 1500
gauss is the minimum required to produce sunspots, Livingston says, at that
level they would no longer be possible.

The phenomenon has happened before. Sunspots disappeared almost entirely 
between
1645 and 1715 during a period called the Maunder Minimum, which 
coincided with
decades of lower-than-normal temperatures in Europe nicknamed the Little 
Ice
Age. But Livingston cautions that the zero-sunspot prediction could be
premature. "It may not happen," he says. "Only the passage of time will 
tell
whether the solar cycle will pick up." Still, he adds, there's no doubt 
that
sunspots "are not very healthy right now." Instead of the robust spots
surrounded by halolike zones called penumbrae, as seen during the last 
solar
maximum (photo), most of the current crop looks "rather peaked," with 
few or no
penumbrae. ...
*****
--
Dave Typinski
AJ4CO Observatory

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