A host of recent observations from space- and ground-based observatories has begun to answer many of the remaining mysteries swirling around sunspots. This 2001 news release from Goddard Space Flight Center, The Sun’s Dark Secret: How Sunspots Pull Themselves Together, reports on scientists getting the first clear picture of what lies beneath sunspots. They observed the flow of electrified gas that creates a self-reinforcing cycle, holding the sunspots together. And recently supercomputers have been used to model the magnetic phenomenon. Go to the University Corporation for Atmospheric Research to view their supercomputer-generated animations of sunspots.
While delving into sunspots on the Internet, I came across a related news story that finally seems to answer a fundamental question of solar physics: How is the Sun’s outermost layer, the corona, heated to a few million degrees kelvin, while the underlying photosphere—where our visible light comes from—hovers at a relatively chilly 5,000 degrees Kelvin? See Giant Solar Twists Discovered to learn about the newly discovered Alfvén waves that heat the corona hot enough to glow in x-ray light. The magnetic twists are named after 1942 Nobel Prize-winner Hannes Alfvén, who had postulated the waves long before today’s proof.
And then there is the two-part question of the day: why so few sunspots, and what might an extended sunspot drought mean for us on Earth? Surprisingly, the first part seems to have an explanation. At NASA, read Mystery of the Missing Sunspots, Solved?, a recent article reporting on the discovery that “a jet stream deep inside the sun is migrating slower than usual through the star’s interior, giving rise to the current lack of sunspots. Rachel Howe and Frank Hill of the National Solar Observatory (NSO) in Tucson, Arizona, used a technique called helioseismology to detect and track the jet stream down to depths of 7,000 km below the surface of the sun. The sun generates new jet streams near its poles every 11 years, they explained to a room full of reporters and fellow scientists. The streams migrate slowly from the poles to the equator and when a jet stream reaches the critical latitude of 22 degrees, new-cycle sunspots begin to appear.”
The second part of the question is not as easy. The solar energy falling on the Earth drops by about a tenth of a percent from the solar cycle peaks to the minimums. (Sunspots, although relatively cool, are accompanied by bright patches called faculae; the result is an overall increase in the amount of radiation sent our way. Go to this NASA page to see the Sun during three different levels of activity.) During the last four centuries that sunspots numbers have been accurately recorded, a period of few spots, called the Maunder Minimum, coincided with what is called the “Little Ice Age” in the second half of the seventeenth century. This observation has lead some to suggest a dearth of sunspots might herald a period of global cooling, eliminating the need to worry about the greenhouse gases we are pumping into the atmosphere. But the consensus of climatologists is that variations in the Sun’s output are small compared with human influences. Read this 2007 article in New Scientist Climate Myths: Global Warming Is Down to the Sun, Not Humans.
While scientists agree that the eleven-year sunspot cycle and its accompanying small variation in solar output have a minimal influence on Earth’s climate compared with recent anthropogenic changes, it appears there may be some links to regional weather. Go the National Science Foundation’s 2007 news report, Link Between Sunspots, Rain Helps Predict Disease in East Africa to read how, statistically, the year before the peak of each cycle experiences unusually heavy rainfall.
In the near future, we are likely to learn more about the earthly effects of sunspots. Despite the relatively minor role solar variation may play in our climate, absolute measurements of total solar irradiance (as the Sun’s output is called) taken from satellites have only be available for three decades. Next April, NASA plans to launch its Glory mission, which will further refine measurements of the Sun’s radiation and how it affects Earth’s energy balance. And, on February 6, 2011—for the first time in human history—we will be able to image the entire Sun and all of its spots. For a press release on the two STEREO spacecraft that will make this possible, go to NASA Sees the ‘Dark Side’ of the Sun.