The pictures studied by Ofman and his colleagues show the shock wave from a solar flare hitting towering arches of hot gas called coronal loops. The shock of the eruption causes the loops to vibrate, a reaction Ofman described as similar to the vibration of a plucked guitar string. That wound up coronal loop would stretch about 35 times the distance from San Diego, Calif. to Portland, Maine. When the solar flare shocked the coronal loop, the immense arch started swinging back and forth at a rate of once every four minutes. Within about an hour, though, the vibration had completely subsided, a fact that surprised Ofman and his co-authors.
Viscosity is a measure of a fluid's resistance to force.
It is harder to shake a stick in mud than in water because mud has a higher viscosity. The quick damping of the coronal loop's vibration means that the corona must be much thicker than previously thought, he said. If this is true, it may explain the corona's tremendous heat. A thick corona would trap heat and provide a mechanism for frictional heat to buildup, but this possibility forces scientists to address the question of how the corona could be so stiff. What could explain the high viscosity, Ofman thinks, is turbulence.