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As has been suggested in
various pages on this site, one of the most powerful potential influences
on our climate is solar activity. A recently published report, an
extract of which is set out below, seems to add weight to the possibility
that we are indeed headed for a new "Maunder Minimum", with all
the serious implications that go with it. During the last solar
Grand Minimum, when crops failed globally, there were only about 500 million
people on the planet. Today we have billions, and the consequences
of a global crop failure would be catastrophic. Food for thought.
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Sunspots are regions of electrically charged,
superheated gas (plasma) on the surface of the sun, formed when upwellings
of the magnetic field trap the ionized plasma. The magnetic field
prevents the gas from releasing the heat and sinking back below the
sun’s surface. These areas are somewhat cooler than the surrounding sun
surface and so appear to us as dark spots.
Sunspots have been observed at least since
the early 17th century, and they are known to follow an 11 year cycle from
solar maximum to solar minimum. The solar minimum usually lasts
around 16 months, but the current minimum has already lasted 26 months,
which is the longest minimum in a hundred years.
Since 1990, Matthew Penn and William
Livingston, solar astronomers with the National Solar Observatory (NSO) in
Tucson
,
Arizona
, have been using a measurement known as Zeeman splitting to study the
magnetic strength of sunspots. The Zeeman splitting is the distance
between a pair of infrared spectral lines in a spectrograph taken of the
light emitted by iron atoms in the atmosphere of the sun. The wider
the distance, the greater is the intensity of the magnetic field.
Penn and Livingston examined 1500 sunspots
and found that the average strength of the magnetic field of the sunspots
has dropped from around 2700 gauss to 2000 gauss (in comparison, the
Earth’s magnetic field is below one gauss). The reasons for the
decline are unknown, but
Livingston
said that if the strength continues to decrease at the same rate it will
drop to 1500 gauss by 2016, and below this strength the formation of
sunspots appears to be impossible.
During the period from 1645 to 1715, a time
known as the Maunder Minimum, there were almost no sunspots. This
period coincided with the Little Ice Age, which produced lower than
average temperatures in
Europe
. Livingston
said their results should be treated with caution as their techniques are
relatively new and it is not yet known if the decline in magnetic field
strength will continue, and that “only the passage of time will tell
whether the solar cycle will pick up.”
David Hathaway, a solar physicist with the
Marshall Space Flight Center in
Huntsville
,
Alabama
, also cautioned the calculations do not take into account that many small
sunspots with relatively weak magnetic fields appeared during the last
solar maximum, and if these are not included in the calculations the
average magnetic field strength would seem higher than it actually was.
Penn and Livingston’s paper has been
submitted to the online colloquium, International Astronomical Union
Symposium No. 273.
More
information:
Long-term Evolution of Sunspot Magnetic Fields, Matthew Penn and William
Livingston, arXiv:1009.0784v1
[astro-ph.SR]
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