Where have all the sunspots gone?

During 2008 and 2009, our sun had the lowest number of sunspots and solar storms of any time during the last century — sunspots essentially disappeared during that two-year period. This lack of sunspots has puzzled astronomers and solar scientists, but a new theory (and supporting data) published in the March 3, 2011 issue of Nature may solve that puzzle. 

“Plasma currents deep inside the sun interfered with the formation of sunspots and prolonged solar minimum,” says lead author Dibyendu Nandi of the Indian Institute of Science Education and Research1 in Kolkata. “Our conclusions are based on a new computer model of the sun’s interior.”

Scientists recognize three distinct (yet interrelated) processes that drive cycles of activity within the sun: the magnetic dynamo, the conveyor belt (shown as black loops in the diagram to the right), and the buoyant evolution of sunspot magnetic fields. Nandi’s team believes they have developed a computer model that gets the physics right for all three processes. For a detailed explanation of how these three processes appear to interact (and how they led to the recent disappearance of sunspots), visit the NASA news article “Researchers crack the mystery of the spotless sun.”

Why should we care?
The sun’s 11-year cycle of activity directly impacts everything from the protection provided by Earth’s ozone layer2 to the operation of our satellites. As just one example, the lack of sunspots during 2008 and 2009 caused space debris to stop decaying and start accumulating in Earth orbit due to increased atmospheric drag. And any increase in orbital debris translates to increased risk of damage to the satellites that provide everything from GPS to weather forecasts.

This research was jointly funded by NASA’s Living with the Stars program and the Department of Science and Technology of the government of India.

All images courtesy of NASA.

1. Ironically I’ve driven past the Institute (located just off the Eastern Bypass in Salt Lake) dozens of times during my stays in Kolkata, but never realized this sort of theoretical work was happening inside. [↩]
2. When solar activity is at a minimum, Earth’s ozone layer decreases, allowing more harmful ultraviolet (UV) rays to penetrate and reach Earth’s surface. Exposure to such UV rays is one major cause of skin cancer. [↩]