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Saul
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A sunspot is a concentrated clump of magnetic energy on the sun's surface that typically varies from 1800 to 3000 Gauss. The Earth's magnetic field strength is in comparison 0.3 Gauss.
Recently Solar physicists have found the magnetic field strength of newly produced sunspots is declining linearly year by year by 50 gauss per year. Why that is happening is not known.
The magnetic ropes that create sunspots are believed to be created deep within the sun at the tachocline zone which is the boundary between the solar convection zone and the radiative zone.
Theoretical calculations indicate that the magnetic ropes that are created at the tachocline require a field strength of around 2000 gauss to avoid being broken up during their rise to the solar surface through the turbulent convection zone. The magnetic ropes rise up through the convection zone to the surface of the sun where they form sunspots. If the trend continues the sun will therefore not be capable of producing new sunspots.
A consequence of the weakening magnetic field of individual sunspots is that the lifetime of recent sunspots is reduced. The typical lifetime of a new sunspot during a normal cycle is around a month. Many of the recently produced weak sunspots break apart in a few days.
http://science.nasa.gov/science-news/science-at-nasa/2009/03sep_sunspots/
http://iopscience.iop.org/1538-4357/649/1/L45/pdf/1538-4357_649_1_L45.pdf
Recently Solar physicists have found the magnetic field strength of newly produced sunspots is declining linearly year by year by 50 gauss per year. Why that is happening is not known.
The magnetic ropes that create sunspots are believed to be created deep within the sun at the tachocline zone which is the boundary between the solar convection zone and the radiative zone.
Theoretical calculations indicate that the magnetic ropes that are created at the tachocline require a field strength of around 2000 gauss to avoid being broken up during their rise to the solar surface through the turbulent convection zone. The magnetic ropes rise up through the convection zone to the surface of the sun where they form sunspots. If the trend continues the sun will therefore not be capable of producing new sunspots.
A consequence of the weakening magnetic field of individual sunspots is that the lifetime of recent sunspots is reduced. The typical lifetime of a new sunspot during a normal cycle is around a month. Many of the recently produced weak sunspots break apart in a few days.
http://science.nasa.gov/science-news/science-at-nasa/2009/03sep_sunspots/
"Sunspot magnetic fields are dropping by about 50 gauss per year," says Penn. "If we extrapolate this trend into the future, sunspots could completely vanish around the year 2015."
This disappearing act is possible because sunspots are made of magnetism. The "firmament" of a sunspot is not matter but rather a strong magnetic field that appears dark because it blocks the upflow of heat from the sun's interior. If Earth lost its magnetic field, the solid planet would remain intact, but if a sunspot loses its magnetism, it ceases to exist.
"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."
http://iopscience.iop.org/1538-4357/649/1/L45/pdf/1538-4357_649_1_L45.pdf
Temporal Changes in Sunspot Umbral Magnetic Field and Temperatures
We have observed high-resolution intensity spectra near the Fe i 1564.8 nm line at a single umbral point corresponding to the darkest position in over 900 sunspots from 1998 through 2005. From these data we determine that the maximum sunspot magnetic fields have been decreasing at about 52 G per year. The same data set shows a concurrent increase in the normalized umbral intensity from 0.60 to 0.75 corresponding to a blackbody temperature rise from 5137 to 5719 K) and a decrease of more than 50% in the molecular OH line strength. The magnetic field and intensity changes observed over time in the sunspot umbrae from different spots behave in the same way as the magnetic field and intensity changes observed spatially across single sunspots.