Sunspots, dark features in the solar photosphere with strong magnetic field, have been observed for more than 400 years. They are the most visible components of regions where solar flares and coronal mass ejections (CMEs) occur, and these eruptive events may cause power outages and interruptions of telecommunication and navigation services on the Earth. Although it is widely believed that sunspot regions are generated in the deep solar interior, the detection of these regions before they emerge from the convection zone into the photosphere has remained undetected until now. Stanford scientists report today the detection of several sunspot regions in the deep interior of the Sun, 1-2 days before they appear on the solar disc. Their results show that sunspots are generated at least 60,000 km below the surface and emerge from this depth up to the surface with an average speed of 0.3-0.6 km/s. The detection of sunspots in the solar interior may provide useful warnings about upcoming surface magnetic activity which can be used to improve and extend the predictions of space weather forecast. The technique that they used to detect the sunspots is called time-distance helioseismology , and it is similar to a technique used by seismologists to image the Earth's interior. The results are reported by Stathis Ilonidis, Junwei Zhao, and Alexander Kosovichev in the paper "Detection of Emerging Sunspot Regions in the Solar Interior" published in the August 19 issue of Science Magazine (vol. 333, pp. 993-996, 2011).
Acoustic travel-time perturbations detected at a depth of about 60,000 km (left) and simultaneous observations of the photospheric intensity (middle) and magnetic field (right). The images of the upper row were taken at about 03:30 UT 26 October 2003 and those of the lower row about 2 days later.
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