ASTROPHYSICS: Glimpsing a Magnetic Carpet

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Science  13 Oct 2006:
Vol. 314, Issue 5797, pp. 224b
DOI: 10.1126/science.314.5797.224b

The surface of the Sun is covered in a granular network of convection cells that are created as ultrahot gas wells up from below. Intense stirring causes magnetic dipoles to grow continually within the cells before being shed into the Sun's atmosphere. By analogy with a woven textile, this distribution of magnetic loops that thread the surface has been dubbed the magnetic carpet. Despite strong theoretical underpinnings, the observational evidence for such a process has been mixed.

McIntosh et al. have marshaled a variety of observations from the SOlar and Heliospheric Observatory (SOHO) satellite to support the magnetic carpet model. They used ultraviolet images of the Sun dispersed into several spectral lines, including ionized silicon, neon, and carbon emissions, to trace the motions of gases at temperatures of tens of thousands to nearly 1 million K across many different cells. The gas velocities were strongest near the edges of the convection cells, and different patterns were observed in quiet Sun regions and coronal holes, consistent with the different magnetic field configurations in those environments. As the magnetic dipoles leave the cells, they release their energy through annihilation. By calculating the amount of energy released, the authors substantiate the importance of the magnetic carpet process in heating the solar corona. — JB

Astrophys. J. astro-ph/0609503 (2006).

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