Slices Through the Solar Interior

The strong magnetic fields in the sunspots promote cooling. Cool material contracts and sinks at speeds of up to 3000 miles per hour. This drives an inward flow, like a planet-sized whirlpool, that holds the sunspot together as long as the field is strong enough. Scientists discovered this using a technique called acoustic tomography - a novel method similar to ultrasound diagnostics in medicine that uses sound waves to image structures inside the human body. Scientists also found that sunspots are surprisingly shallow. Conditions in sunspots change from cooler than the surrounding plasma to hotter than the surrounding plasma just 3000 miles below the surface. The cool part of a sunspot has the shape of a stack of two or three nickels. Sunspot magnetic fields block the flows that carry heat energy up from the hot solar interior. That results in higher temperatures below the blockage and cooler temperatures above. The downward flows mentioned above dissipate at the same depth. With these data one cannot get a sharp enough picture to really explain the details. Understanding sunspots is essential for understanding the 11-year solar cycle, solar flare explosions, and huge coronal mass ejections that affect life and society on Earth.