ARLA/CLUSTER: Mínimo anómalo de manchas solares ou nova Idade do Gelo depois de 2015..?

[João Gonçalves Costa]

[http://www.norcalblogs.com/watts/images/sunspots_earth_size_big.jpg]<http://www.norcalblogs.com/watts/images/sunspots_earth_size_big.jpg>

William Livingston e Matt Penn, investigadores do Observatório Nacional Solar - Tucson: EUA - dizem que o nosso Sol, a partir de 2015, poderá perder as suas manchas solares, denotando menos actividade, o que poderá levar a uma nova pequena idade do gelo - como no Maunder Minimum (Mínimo de Maunder), entre 1645 e 1715 quando a actividade de manchas solares reduziu-se drasticamente, gerando na Terra uma redução dramática da temperatura. No continente europeu e América do Norte registraram-se temperaturas baixíssimas, provocando o congelamento de grandes cursos de rios que normalmente não passam por essa situação. O nome "Maunder" deve-se ao astrónomo inglês E. W. Maunder (1851-1929) do Observatório de Greenwich, que o relatou quando estudava os registos históricos sobre o Sol
Are sunspots disappearing?

Nasa report that the sun is in the pits of the deepest solar minimum in nearly a century. Weeks and sometimes whole months go by without even a single tiny sunspot. The quiet has dragged out for more than two years, prompting some observers to wonder, are sunspots disappearing?

"Personally, I'm betting that sunspots are coming back," says researcher Matt Penn of the National Solar Observatory (NSO) in Tucson, Arizona. But, he allows, "there is some evidence that they won't."

Penn's colleague Bill Livingston of the NSO has been measuring the magnetic fields of sunspots for the past 17 years, and he has found a remarkable trend. Sunspot magnetism is on the decline.

While most researchers measure the splitting of spectral lines in the visible part of the sun's spectrum, Livingston decided to try an infra-red spectral line. Infrared lines are much more sensitive to the Zeeman effect and provide more accurate answers. Also, he dedicated himself to measuring a large number of sunspots-more than 900 between 1998 and 2005 alone. The combination of accuracy and numbers revealed the downturn.

"According to our measurements, sunspots seem to form only if the magnetic field is stronger than about 1500 gauss," says Livingston.

"If the current trend continues, we'll hit that threshold in the near future, and solar magnetic fields would become too weak to form sunspots."

"This work has caused a sensation in the field of solar physics," comments NASA sunspot expert David Hathaway, who is not directly involved in the research. "It's controversial stuff."

If sunspots do go away, it wouldn't be the first time.
In the 17th century, the sun plunged into a 70-year period of spotlessness known as the Maunder Minimum that still baffles scientists. The sunspot drought began in 1645 and lasted until 1715; during that time, some of the best astronomers in history (e.g., Cassini) monitored the sun and failed to count more than a few dozen sunspots per year, compared to the usual thousands.

"Whether [the current downturn] is an omen of long-term sunspot decline, analogous to the Maunder Minimum, remains to be seen," Livingston and Penn caution in a recent issue of EOS. "Other indications of solar activity suggest that sunspots must return in earnest within the next year."

Whatever happens, notes Hathaway, "the sun is behaving in an interesting way and I believe we're about to learn something new."

Read the full NASA report at

http://science.nasa.gov/headlines/y2009/
03sep_sunspots.htm?list130845
Fontes: Blog Ano Zero e Southgate Amateur Radio Club.
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