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The Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory (SDO) has allowed a team of researchers of the University of Central Lancashire to follow, over a period of several hours, the formation of a sunspot in unprecedented detail.
This detail is not so much in the images of the photosphere in the active regions, where images have long been available at very high resolution, but rather in the detailed features traced in the magnetic field.
Sunspots, whether single or in large groups, are the most visible consequence of magnetic flux tubes that pass from the Sun's convective zone, through the photosphere and chromosphere and into the surrounding corona.
The SDO can observe all these environments, in particular the chromosphere and corona, and can study rapid temperature fluctuations in the range 50 thousand to 10 million degrees.
This capability has allowed this research team, led by Stephane Regnier, to follow the birth and evolution of a group of spots from the photosphere to the corona, and trace the evolution of the associated magnetic flux tube via the behaviour of the surrounding material.
The first sign of the appearance of an active region studied by the British team (between the end of May and the beginning of June, 2010) were small areas of opposing magnetic polarity (white = positive, black = negative in the above images) separated by about 7000 km. After 5 hours the area of disturbed magnetic field had grown to cover an area roughly 20,000 km across, comparable in size to the so-called "super granules" (groupings of granules).
Granules represent the convective cells at the Sun's surface, similar to those that form in boiling soup.
It was expected that the first pore (tiny sunspot with no penumbra) would be seen at the centre of a super granule, but instead it was observed to appear at its edge; something that models aimed at explaining the development of sunspots will now have to take into account.
The results of this work were presented yesterday in Llandudno, Wales, at the National Astronomy Meeting of the Royal Astronomical Society.
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