LATELY, the Sun has been behaving a bit strangely. In 2008 and
2009, it showed the least surface activity in nearly a century. Solar flare
activity stopped cold and weeks and months went by without any sunspots, or
areas of intense magnetism. Quiet spells are normal for the Sun, but researchers
alive today had never seen anything like that two-year hibernation.
Now that the Sun is approaching the peak of its magnetic cycle, when solar
storms — blasts of electrically charged magnetic clouds — are most likely to
occur, no one can predict how it will behave. Will solar activity continue to be
sluggish, or will solar storms rage with renewed vigor?
Luckily, policy makers are paying attention to space weather. Late last month,
President Obama and the British prime minister David Cameron announced that the
United States and Britain will work together to create “a fully operational
global space weather warning system.” And just last week, the United Nations
pledged to upgrade its space weather forecasts.
But most people have never heard of space weather, which is a problem, because
both high and low solar activity have serious effects on life on Earth.
Modern society depends on a variety of technologies that are susceptible to the
extremes of space weather. Spectacular explosions on the Sun’s surface produce
solar storms of intense magnetism and radiation. These events can disrupt the
operation of power grids, railway signaling, magnetic surveying and drilling for
oil and gas. Magnetic storms also heat the upper atmosphere, changing its
density and composition and disrupting radio communications and GPS units. The
storms’ charged particles can be a hazard to the health of astronauts and
passengers on high altitude flights.
Severe storms in 1989 and 2003 caused blackouts in Canada and Sweden. In 1859, a
solar super storm sparked fires in telegraph offices. Such storms are predicted
every century or so, and perhaps we’re overdue. According to a 2008 National
Academies report, a once-in-a-century solar storm could cause the financial
damage of 20 Hurricane Katrinas.
A quiet Sun causes its own problems. During the two-year quiet spell, our upper
atmosphere, normally heated and inflated by the Sun’s extreme ultraviolet
radiation, cooled off and shrank. This altered the propagation of GPS signals
and slowed the rate of decay of space debris in low Earth orbit. In addition,
the cosmic rays that are normally pushed out to the fringes of the solar system
by solar explosions instead surged around Earth, threatening astronauts and
satellites with unusually high levels of radiation.
The more we know about solar activity, the better we can protect ourselves. The
Sun is surrounded by a fleet of spacecraft that can see sunspots forming, flares
crackling and a solar storm about 30 minutes before it hits Earth. NASA and the
National Science Foundation have also developed sophisticated models to predict
where solar storms will go once they leave the Sun, akin to National Weather
Service programs that track hurricanes and tornadoes on Earth. Thanks to these
sentries, it is increasingly difficult for the Sun to take us by surprise.
If alerted, Internet server hubs, telecommunications centers and financial
institutions can prepare for disruptions and power plant operators can
disconnect transformers.
But what good are space weather alerts if people don’t understand them and won’t
react to them? Consider the following: If anyone should be familiar with the
risks of space weather, it’s a pilot. During solar storms, transpolar flights
are routinely diverted because the storms can disrupt the planes’ communications
equipment. And yet a space weather forecaster we know at the National Oceanic
and Atmospheric Administration often tells a story of a conversation he had with
a pilot:
Pilot: “What do you do for a living?”
Forecaster: “I forecast space weather.”
Pilot: “Really? What’s that?”
The point of the story is to highlight how far the scientific community and the
government have to go to raise awareness about space weather and its effects.
With the sun waking up, trans-Atlantic cooperation comes at just the right time.
Let us hope it is only the beginning of a worldwide effort to forecast and
understand space weather.
Madhulika Guhathakurta is a solar physicist at NASA.
Ever since Samuel Heinrich Schwabe, a German astronomer, first noted in 1843
that sunspots burgeon and wane over a roughly 11-year cycle, scientists have
carefully watched the Sun’s activity. In the latest lull, the Sun should have
reached its calmest, least pockmarked state last fall.
Indeed, last year marked the blankest year of the Sun in the last half-century —
266 days with not a single sunspot visible from Earth. Then, in the first four
months of 2009, the Sun became even more blank, the pace of sunspots slowing
more.
“It’s been as dead as a doornail,” David Hathaway, a solar physicist at NASA’s
Marshall Space Flight Center in Huntsville, Ala., said a couple of months ago.
The Sun perked up in June and July, with a sizeable clump of 20 sunspots earlier
this month.
Now it is blank again, consistent with expectations that this solar cycle will
be smaller and calmer, and the maximum of activity, expected to arrive in May
2013 will not be all that maximum.
For operators of satellites and power grids, that is good news. The same roiling
magnetic fields that generate sunspot blotches also accelerate a devastating
rain of particles that can overload and wreck electronic equipment in orbit or
on Earth.
A panel of 12 scientists assembled by the National Oceanic and Atmospheric
Administration now predicts that the May 2013 peak will average 90 sunspots
during that month. That would make it the weakest solar maximum since 1928,
which peaked at 78 sunspots. During an average solar maximum, the Sun is covered
with an average of 120 sunspots.
But the panel’s consensus “was not a unanimous decision,” said Douglas A.
Biesecker, chairman of the panel. One member still believed the cycle would roar
to life while others thought the maximum would peter out at only 70.
Among some global warming skeptics, there is speculation that the Sun may be on
the verge of falling into an extended slumber similar to the so-called Maunder
Minimum, several sunspot-scarce decades during the 17th and 18th centuries that
coincided with an extended chilly period.
Most solar physicists do not think anything that odd is going on with the Sun.
With the recent burst of sunspots, “I don’t see we’re going into that,” Dr.
Hathaway said last week.
Still, something like the Dalton Minimum — two solar cycles in the early 1800s
that peaked at about an average of 50 sunspots — lies in the realm of the
possible, Dr. Hathaway said. (The minimums are named after scientists who helped
identify them: Edward W. Maunder and John Dalton.)
With better telescopes on the ground and a fleet of Sun-watching spacecraft,
solar scientists know a lot more about the Sun than ever before. But they do not
understand everything. Solar dynamo models, which seek to capture the dynamics
of the magnetic field, cannot yet explain many basic questions, not even why the
solar cycles average 11 years in length.
Predicting the solar cycle is, in many ways, much like predicting the stock
market. A full understanding of the forces driving solar dynamics is far out of
reach, so scientists look to key indicators that correlate with future events
and create models based on those.
For example, in 2006, Dr. Hathaway looked at the magnetic fields in the polar
regions of the Sun, and they were strong. During past cycles, strong polar
fields at minimum grew into strong fields all over the Sun at maximum and a
bounty of sunspots. Because the previous cycle had been longer than average, Dr.
Hathaway thought the next one would be shorter and thus solar minimum was
imminent. He predicted the new solar cycle would be a ferocious one.
Instead, the new cycle did not arrive as quickly as Dr. Hathaway anticipated,
and the polar field weakened. His revised prediction is for a
smaller-than-average maximum. Last November, it looked like the new cycle was
finally getting started, with the new cycle sunspots in the middle latitudes
outnumbering the old sunspots of the dying cycle that are closer to the equator.
After a minimum, solar activity usually takes off quickly, but instead the Sun
returned to slumber. “There was a long lull of several months of virtually no
activity, which had me worried,” Dr. Hathaway said.
The idea that solar cycles are related to climate is hard to fit with the actual
change in energy output from the sun. From solar maximum to solar minimum, the
Sun’s energy output drops a minuscule 0.1 percent.
But the overlap of the Maunder Minimum with the Little Ice Age, when Europe
experienced unusually cold weather, suggests that the solar cycle could have
more subtle influences on climate.
One possibility proposed a decade ago by Henrik Svensmark and other scientists
at the Danish National Space Center in Copenhagen looks to high-energy
interstellar particles known as cosmic rays. When cosmic rays slam into the
atmosphere, they break apart air molecules into ions and electrons, which causes
water and sulfuric acid in the air to stick together in tiny droplets. These
droplets are seeds that can grow into clouds, and clouds reflect sunlight,
potentially lowering temperatures.
The Sun, the Danish scientists say, influences how many cosmic rays impinge on
the atmosphere and thus the number of clouds. When the Sun is frenetic, the
solar wind of charged particles it spews out increases. That expands the cocoon
of magnetic fields around the solar system, deflecting some of the cosmic rays.
But, according to the hypothesis, when the sunspots and solar winds die down,
the magnetic cocoon contracts, more cosmic rays reach Earth, more clouds form,
less sunlight reaches the ground, and temperatures cool.
“I think it’s an important effect,” Dr. Svensmark said, although he agrees that
carbon dioxide is a greenhouse gas that has certainly contributed to recent
warming.
Dr. Svensmark and his colleagues found a correlation between the rate of
incoming cosmic rays and the coverage of low-level clouds between 1984 and 2002.
They have also found that cosmic ray levels, reflected in concentrations of
various isotopes, correlate well with climate extending back thousands of years.
But other scientists found no such pattern with higher clouds, and some other
observations seem inconsistent with the hypothesis.
Terry Sloan, a cosmic ray expert at the University of Lancaster in England, said
if the idea were true, one would expect the cloud-generation effect to be
greatest in the polar regions where the Earth’s magnetic field tends to funnel
cosmic rays.
“You’d expect clouds to be modulated in the same way,” Dr. Sloan said. “We can’t
find any such behavior.”
Still, “I would think there could well be some effect,” he said, but he thought
the effect was probably small. Dr. Sloan’s findings indicate that the cosmic
rays could at most account for 20 percent of the warming of recent years.
Even without cosmic rays, however, a 0.1 percent change in the Sun’s energy
output is enough to set off El Niño- and La Niña-like events that can influence
weather around the world, according to new research led by the National Center
for Atmospheric Research in Boulder, Colo.
Climate modeling showed that over the largely cloud-free areas of the Pacific
Ocean, the extra heating over several years warms the water, increasing
evaporation. That intensifies the tropical storms and trade winds in the eastern
Pacific, and the result is cooler-than-normal waters, as in a La Niña event, the
scientists reported this month in the Journal of Climate.
In a year or two, the cool water pattern evolves into a pool of El Niño-like
warm water, the scientists said.
New instruments should provide more information for scientists to work with. A
1.7-meter telescope at the Big Bear Solar Observatory in Southern California is
up and running, and one of its first photographs shows “a string of pearls,”
each about 50 miles across.
“At that scale, they can only be the fundamental fibril structure of the Sun’s
magnetic field,” said Philip R. Goode, director of the solar observatory. Other
telescopes may have caught hints of these tiny structures, he said, but “never
so many in a row and not so clearly resolved.”
Sun-watching spacecraft cannot match the acuity of ground-based telescopes, but
they can see wavelengths that are blocked by the atmosphere — and there are
never any clouds in the way. The National Aeronautics and Space Administration’s
newest sun-watching spacecraft, the Solar Dynamics Observatory, which is
scheduled for launching this fall, will carry an instrument that will
essentially be able to take sonograms that deduce the convection flows
generating the magnetic fields.
That could help explain why strong magnetic fields sometimes coalesce into
sunspots and why sometimes the strong fields remain disorganized without forming
spots. The mechanics of how solar storms erupt out of a sunspot are also not
fully understood.
A quiet cycle is no guarantee no cataclysmic solar storms will occur. The
largest storm ever observed occurred in 1859, during a solar cycle similar to
what is predicted.
Back then, it scrambled telegraph wires. Today, it could knock out an expanse of
the power grid from Maine south to Georgia and west to Illinois. Ten percent of
the orbiting satellites would be disabled. A study by the National Academy of
Sciences calculated the damage would exceed a trillion dollars.
But no one can quite explain the current behavior or reliably predict the
future.
“We still don’t quite understand this beast,” Dr. Hathaway said. “The theories
we had for how the sunspot cycle works have major problems.”
October 3, 2008
The New York Times
By KENNETH CHANG
The Sun has been strangely
unblemished this year. On more than 200 days so far this year, no sunspots were
spotted. That makes the Sun blanker this year than in any year since 1954, when
it was spotless for 241 days.
The Sun goes through a regular 11-year cycle, and it is now emerging from the
quietest part of the cycle, or solar minimum. But even for this phase it has
been unusually quiet, with little roiling of the magnetic fields that induce
sunspots.
“It’s starting with a murmur,” said David H. Hathaway, a solar physicist at
NASA’s Marshall Space Flight Center in Huntsville, Ala.
As of Thursday, the 276th day of the year, the National Oceanic and Atmospheric
Administration’s Space Weather Prediction Center in Boulder, Colo., had counted
205 days without a sunspot.
In another sign of solar quiescence, scientists reported last month that the
solar wind, a rush of charged particles continually spewed from the Sun at a
million miles an hour, had diminished to its lowest level in 50 years.
Scientists are not sure why this minimum has been especially minimal, and the
episode is even playing into the global warming debate. Some wonder if this
could be the start of an extended period of solar indolence that would more than
offset the warming effect of human-made carbon dioxide emissions. From the
middle of the 17th century to the early 18th, a period known as the Maunder
Minimum, sunspots were extremely rare, and the reduced activity coincided with
lower temperatures in what is known as the Little Ice Age.
Compared to the Maunder Minimum, the current pace of sunspots “makes it look
like we’re having a feast, not a famine,” Dr. Hathaway said.
Scientists expect that sunspot activity will pick up in the coming months, but
exactly what will happen next is open to debate. Dr. Hathaway had predicted two
years ago, based on the Sun’s behavior near the end of the last cycle, that the
maximum this time would be ferocious.
“I’m getting worried about that prediction now,” he said. “Normally, big cycles
start early, and by doing that, they cut short the previous cycle. This one
hasn’t done that.”
But many of the other competing predictions — more than 50 over all — pointed to
a quieter-than-average cycle. “They do kind of go all over the map,” said
Douglas Biesecker, a physicist at the Space Weather Prediction Center who led an
international panel that reviewed predictions.
The solar wind is another piece of the puzzle. David J. McComas of the Southwest
Research Institute in San Antonio and one of the researchers who analyzed data
from the Ulysses Sun-watching spacecraft, said that the strength of the solar
wind seemed to be in a long-term decline. The pressure exerted by the solar wind
particles during the current minimum is about a quarter weaker than during the
last solar minimum, Dr. McComas said.
Dr. McComas said scientists were still trying to figure out how all the data
fits together.
“There are a number of researchers who predict the next solar cycle,” he said.
“There are also a number of investment counselors who predict the future of the
stock market.”
