Link to paper at http://www.sciencemag.org/content/333/6045/993.full
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 emergence of these regions through
the convection zone to 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. Click on the image for full resolution.|
|Images of surface and subsurface magnetic activity of active region 10488. The upper layer shows the photospheric magnetic field, and the lower layer shows the acoustic travel-time perturbations detected at a depth of about 60,000 km. The upper image was taken at about 03:30 UT 26 October 2003 and the lower image about 2 days later. Click on the image for full resolution.|
|Images of surface and subsurface magnetic activity of active region 11158. The upper layer shows the photospheric intensity, and the lower layer shows the acoustic travel-time perturbations detected at a depth of about 60,000 km. The upper image was taken at about 03:30 UT 11 February 2011 and the lower image about 2 days later. Click on the image for full resolution.|
|A full disk image of the Sun showing a few sunspot groups in the photosphere, observed by SOHO/MDI after AR10488 emergence.|
|A full disk image of the Sun showing the sunspot group in AR11158 after emergence, observed by SDO/HMI.|
|Acoustic ray paths with lower turning points between 42 and 75 Mm crossing a region of emerging flux.|
|Schematic representation of the measurement scheme. The oscillation signal is averaged inside each arc and cross-correlations are computed between arcs of the same color. For simplicity only arcs with size of 45 degrees and one specific orientation are shown here.|
|Movie showing the detected travel-time perturbations before the emergence of active region 10488 in the photosphere. The first 10 seconds of the movie show intensity observations of the Sun. The intensity later fades out and the photospheric magnetic field is shown. In the next 20 seconds, we zoom in to a region where a sunspot group would emerge. The upper layer shows magnetic field observations at the surface and the lower layer shows simultaneous travel-time perturbations, detected at a depth of about 60,000 km. After the emergence, intensity observations show the full development of this active region, until it rotates out of view on the west solar limb. (movie made by Thomas Hartlep)||Movie showing the detected travel-time perturbations during the emergence of active region 11158. The first 12 seconds of the movie show photospheric intensity observations (orange color) of the region, and travel-time perturbations detected at a depth of about 60,000 km (blue-red color). The movie then shows sunspots (blue and orange) on the solar surface and coronal loops (light green) observed by SDO/AIA. (movie made by Thomas Hartlep and Scott Winegarden).|
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Suggested image credit for data from SDO/HMI: Courtesy of NASA/SDO and the HMI science teams.