Sanford Researchers Use Acoustic Waves to Predict Sunspots

August 25, 2011

GPS, satellites and power grids can be disrupted by solar storms. Stanford University researcher have developed a way to detect emerging sunspots before they appear on the sun's surface.

"Many solar physicists tried different ways to predict when sunspots would appear, but with no success," said Phil Scherrer, a professor of physics in the Stanford lab where the research was conducted."

The new method uses acoustic waves generated inside the sun by the turbulent motion of plasma and gases in constant motion. Small-scale convection cells generate sound waves the travel to the interior of the sun and are reflected back to the surface. Stathis Ilonidis, a Stanford graduate student in physics, was able to use masses of data from NASA's Solar and Heliospheric Observatory satellite, known as SOHO, and its recently launched Solar Dynamics Observatory satellite, which carries the Helioseismic and Magnetic Imager, to develop a way to reduce noise in the data so the team could accurately measure the solar sounds.

"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."

Those perturbations tip the researchers that a sunspot is forming.

Ilonidis added, "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. We have now successfully detected them four times and tracked them moving upward at speeds between 1,000 and 2,000 kilometers per hour."

The solar acoustic system is able to provide a two-day warning. One of the goals is to achieve a three-day warning of impending solar storms, allowing additional time to prepare for it.

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