August 24th, 2011 by Michael Ricciardi
The ‘Music of the (Helio) Sphere’? – Standford University physicists have developed a method for predicting the emergence of sunspots and the solar flares that they spawn. The new method can detect the unique acoustic wave patterns that signal the appearance of sunspots with as little as 24 hours lead time.
Thousands of kilometers beneath the sun’s surface, roiling plasma and gases generate turbulent magnetic fields which rise to the solar surface. There, smaller-scale convection cells (roughly the size of California) refract this energy in the form of sound waves back to the Sun’s interior where they are once again bounced back to the surface.
Combining data from two NASA solar satellites with seismic data from Earth, scientists can now detect these magnetic field fluxes and predict a large sunspot’s appearance in as little as 24 hours. Smaller sunspots have a lead time of up to two days.
The key discoveries made is that the time it takes for a sound wave to return to the surface will vary depending upon the presence of magnetic fields in its travel path. Also, large spots travel faster than smaller ones (thus the difference in lead times). This variance (or “anomaly”) can be detected if the background “noise” is reduced or eliminated. Stathis Ilonidis, a Stanford graduate student in physics, developed a method of reducing the “electronic clutter” in the data so he could accurately measure the solar sounds.
From the Stanford University News press release:
“We know enough about the structure of the Sun that we can predict the travel path and travel time of an acoustic wave as it propagates through the interior of the Sun,” said Junwei Zhao, a senior research scientist at Stanford’s Hansen Experimental Physics Lab. “Travel times get perturbed if there are magnetic fields located along the wave’s travel path.”
Millions of data points between interior and surface have to be measured to predict the anomalies; comparing and measuring these points allows scientist to predict where (and how large) a sunspot is likely to emerge.
Watch the video showing the method for detecting the solar acoustic waves (article continues below):
Video: Detection of Emerging Sunspot Regions – 18 August 2011: 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) Courtesy of the Helioseismic and Magnetic Imager.
Sunspots can generate powerful solar flares which sometimes trigger coronal mass ejections (CMEs) composed of high-energy particles that shoot out into space. This is known as the solar wind — sometimes referred to generally as “space weather” — which can cause power grids to malfunction, shut down satellite communications, and pose a serious hazard to astronauts. Up until now, there has been no reliable means of detecting or predicting when these spots will appear.
So, being able to detect these acoustic wave anomalies associated with the appearance of sun spots means better space weather prediction. And that can give people on Earth time to prepare and take precautions.
The new method can detect the formation of early-stage sunspots as deep as 65,000 kilometers.
“Researchers have suspected for a long time that sunspot regions are generated in the deep solar interior, but until now the emergence of these regions through the convection zone to the surface had gone undetected,” Ilonidis said. “We have now successfully detected them four times and tracked them moving upward at speeds between 1,000 and 2,000 kilometers per hour.”
Researchers used data from the Michelson Doppler Imager aboard NASA’s Solar and Heliospheric Observatory (SOHO) and combined it with data from another NASA satellite — the Solar Dynamics Observatory satellite (SDO) which carries the Helioseismic and Magnetic Imager. Additionally, seismic data from Earth was used to help identify the unique acoustic wave patterns that precede the emergence of sunspots.
Funding for this research came form NASA’s Living with a Star program.
Top image: NASA
Video: Thomas Hartlep, Courtesy of the Helioseismic and Magnetic Imager.
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