How sun's magnetic field is formed

Washington, August 29 : Scientists have solved one of few remaining fundamental mysteries about how the Sun works.

The mechanism, known as meridional flow, works something like a conveyor belt. Magnetic plasma migrates north to south on the Sun's surface, from the equator to the poles, and then cycles into the Sun's interior on its way back to the equator.

The rate and depth beneath the surface of the Sun at which this process occurs is critical for predicting the Sun's magnetic and flare activity, but has remained largely unknown until now.

The solar scientists used the Stanford-operated Helioseismic and Magnetic Imager (HMI) - an instrument onboard NASA's Solar Dynamics Observatory satellite - to track solar waves in much the way seismologists would study seismic movements beneath the surface of the Earth. Every 45 seconds for the past two years, the HMI's Doppler radar snapped images of plasma waves moving across the Sun's surface.

By identifying patterns of sets of waves, the scientists could recognize how the solar materials move from the Sun's equator toward the poles, and how they return to the equator through the Sun's interior.

Lead author Junwei Zhao, a senior research scientist at the Hansen Experimental Physics Laboratory at Stanford said that once they understood how long it takes the wave to pass across the exterior, they determined how fast it moves inside, and thus how deep it goes.

Although solar physicists have long hypothesized such a mechanism, at least in general terms, the new observations redefine solar currents in a few ways.

First, the returning currents occur 100,000 kilometers below the surface of the Sun, roughly half as deep as suspected. As such, solar materials pass through the interior and return to the equator more quickly than hypothesized.

Zhao said that more startling is that the equator-ward flow is actually sandwiched between two 'layers' of pole-ward currents, a more complicated mechanism than previously thought, and one that could help refine predictions of the Sun's activity.

--ANI (Posted on 29-08-2013)

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