The images from cameras and sensors on the latest satellite watching the sun are a dramatic reminder of the awesome power of the star that warms our planet. They show clouds of magnetized gas big enough to engulf the Earth breaking away from the outermost layer of the sun’s atmosphere. These coronal mass ejections (CMEs), which are usually accompanied by solar flares with the explosive force of millions of atomic bombs, can last for several hours and travel through space at over 1 million kilometers per hour. Yet the sun has been in one of its quietest recorded phases for a century. The sun’s activity ebbs and flows in a cycle that averages about 11 years.
Sunspots, vast dark areas on the sun created by strong magnetic fields beneath its surface, provide a visual guide to the evolution of the solar cycle, appearing in large numbers at the time of maximum activity and all but disappearing during the minimum.
NASA launched its Solar Dynamics Observatory satellite in February not just to gain a better understanding of how the sun behaves and why, but also to keep a closer watch on space weather.
Since the spacecraft and its instruments were officially commissioned on May 14, more than 5 million images have poured in. If there are no malfunctions, they will keep coming at a rate of about 70,000 each day for at least the next five years.
The satellite has shown that it can check the sun’s activity faster and in greater depth and detail than any previous observatories on land or in space. This is breaking barriers of timeliness and clarity that have long blocked progress in forecasting dangerous solar storms.
CMEs usually take about three days reach Earth, but very fast ones can arrive in under a day. The charged particles and magnetic forces emit radiation across the electromagnetic spectrum, from low-energy radio waves through to high-energy gamma rays, as they penetrate the outermost layer of Earth’s atmosphere, the ionosphere.
If the geomagnetic storm is violent enough, it can interfere with high- technology networks on which Japan and other advanced economies increasingly depend. Electricity supply grids, satellite navigation, air travel, financial services and radio communications, including mobile-phone networks, could all be disrupted for hours or even days.
A major solar storm in 1989 shut the Quebec power grid in Canada for nine hours. Another storm in 2003 caused satellite problems around the world.
A 2008 report by the U.S. National Academy of Sciences warned that a once-in-a-century space storm striking network-dependent America today could cause 20 times more economic damage than Hurricane Katrina in 2005.
Now that solar activity appears to be on the rise again, scientists are trying to work out when the next peak will occur, how severe it will be, and how long it will last. The U.S. National Oceanic and Atmospheric Administration said last year that the next solar maximum was expected to occur in May 2013 and that the whole cycle would be below average in intensity. But there is considerable uncertainty attached to such predictions.
Since the space age began in the 1950s, solar activity has generally been high. Five of the 10 most intense solar cycles on record have occurred in the last 50 years. Researchers will use the new solar images and data from the NASA satellite and several other spacecraft due to be launched later this year to try to determine the extent to which the sun may be heating or cooling the Earth, and thus contributing to climate change.
This is a controversial issue. For more than two centuries, scientists have wondered how much heat and light the sun expels, and whether this energy varies enough to change Earth’s climate. Since NASA launched its first satellite carrying a radiometer in 1978 to measure the amount of sunlight striking the top of Earth’s atmosphere, researchers have realized that this total irradiance fluctuates. It is not constant, as was previously thought.
Measurements collected in the 1980s and 1990s provided evidence that irradiance is a balance between darkening from sunspots and brightening from hotter regions called faculae, a Latin word meaning “bright torch.”
Sunspots appear dark because they are cooler than surrounding areas. They are footprints of magnetic restraining loops pushing through the solar surface and holding the hot plasma below. When solar activity increases, both sunspots and faculae become more numerous. But during the peak of the cycle, the faculae brighten the sun more than sunspots dim it.
However, the recorded variations in solar irradiance are small, prompting many scientists to conclude that only the emission of rapidly rising amounts of greenhouse gases from human activity in recent decades could have been largely responsible for global warming.
A study published in March concluded that the average world sea and land surface temperature was likely to rise by between 3.7 and 4.5 degrees Celsius by 2100 if fossil-fuel burning and deforestation continue. The increase in greenhouse gas emissions driving this warming trend would be far greater than the impact of any known shifts in solar energy output.
Michael Richardson is a visiting senior research fellow at the Institute of Southeast Asian Studies in Singapore.