The Rowdy and Quiet Sun

People have become familiar with the fact that climate change not only involves global warming but also greater extremes in weather. Rare but damaging events like tornados and hurricanes and floods appear to be increasing.27 Another type of weather that can impact human affairs is space weather. In addition to emitting a continu­ous stream of superhot hydrogen and helium called the solar wind, the Sun periodically ejects billions of tons of plasma in a cataclysm called a coronal mass ejection. Researchers think this happens when magnetic fields are stretched and then snap into a different arrangement, like rubber bands pulled to the breaking point.28 The ejections are huge clouds of material, as much as 10 billion tons of hot gas, and when they head toward us, they can cause fierce magnetic storms in the upper atmosphere. This extreme “weather” in space can impact the functioning and the reliability of technol­ogy on the ground and in low Earth orbit. Strong electromagnetic fields resulting from space weather induce surging currents in elec­trical wires, disrupt power transmission lines, cause widespread blackouts, and affect the infrastructure that forms the backbone of the Internet. Power grids are particularly vulnerable to electrical overloads caused by space storms. Extremes of space weather also dislocate the radiation belts, and damage the satellites used for essential functions like telecommunications, weather forecasting, and GPS or global positioning systems.

Throughout history, people at high latitudes have experienced the Sun-Earth interaction through auroras, but the effect is not always benign. We’ve already seen that in the dog days of summer in 1859, telegraph wires in the United States and Europe spon­taneously shorted out and caused numerous fires. Soon after, the northern lights (or Aurora Borealis) were observed as far south as Rome and Hawaii. This was a “perfect storm” in space, where several changes conspired to produce a mammoth solar flare. The 1859 solar storm was the strongest ever recorded and it occurred when electrical technology was in its infancy. A weaker storm in 1921 induced ground current strong enough to shut down the New York City subway system. Much weaker storms in 1989 and 1994 knocked out communication satellites and parts of the North American power grid.

Arthur C. Clarke’s visionary proposal in 1945 in a letter to the editor of Wireless World to place communication and television satellites in geostationary orbit helped launch the Information Age. As of October 2009, the U. S. Satellite Database listed over 13,000 operating satellites in Earth orbit.29 In 2001, it was estimated that the satellite fleet in Earth orbit was worth $100 billion.30 During a single solar storm, billions of dollars of this orbiting hardware can be destabilized or destroyed. After the 1989 storm, Sten Odenwald reports that “satellites in polar orbits actually tumbled out of con­trol for hours” as others attempted to “flip upside down.”31 John Freeman explains why solar storms can decimate satellites despite their sophisticated electronics: “Storms in space produce miniature lightning storms on the surface of the satellite” and “immerse the satellites in a ‘cloud’ of hot electrons” that mimic commands from ground operators but are in fact phantom commands.32 If the cost of a fleet of satellites seems detached from our everyday existence, consider days or weeks without Internet access or GPS for vehicles, or communication and navigation systems for airline and ocean liner transport, cargo shipping, and road transport. Solar storms can even affect oil pipelines, which undergo accelerated corrosion from the bombardment of charged particles streaming from the Sun, eventually causing breaches in the pipeline.33

Space weather prediction remains an emerging science spear­headed by NASA, ESA, and the United Nations Office of Outer Space Affairs. Data from SOHO, and increasing concern over the impact of space weather, caused NASA to commission a new study in 2009. The resulting report provides clear economic data to quantify the risk to the near-Earth environment from episodes of intense solar activity. Extreme space weather is in a category with other natural hazards that are rare but have far-reaching con­sequences, like major earthquakes and tsunamis.34 It’s likely that more than once in the next twenty years there will be an “electro­jet disturbance” that disrupts the national power grid. In the 1989 event, the loss of some portions of the grid put stress on others and led to a cascade affect. The end result was power outages affecting more than 130 million people and covering half the country.

SOHO cannot prevent these natural disasters, but it can give two or three days’ notice of Earth-directed disturbances. And as we become more accurate in anticipating space storms, operators can place satellites in protective modes, shut down or limit power grids, redirect commercial flights, warn oceanic cruise and cargo ships, and place astronauts working on the International Space Station in the safest possible location on the station. Such steps will not only save lives but also protect the information systems that sustain our electronically fragile and networked global community.

Although SOHO’s bread and butter is looking for the high – energy radiation that’s a hallmark of solar activity, there was a recent concern that the Sun is becoming too inactive. Through 2008 and 2009 there were fewer and fewer sunspots. In part this was due to the natural solar cycle, but the calm was eerie. Entire months would go by without a single blemish on the Sun, and the solar minimum was as deep as it has been in a century. Bill Livings­ton and Matt Penn of the National Solar Observatory made the unsettling discovery that the magnetism of sunspots is declining by about 50 Gauss per year.35 Since sunspots have no substance— they’re just dim, cool markers of a concentration of magnetism— the worry is that the magnetic field would drop below 1500 Gauss, at which point no sunspots can form at all. Did decline like this presage a return to the Maunder Minimum of the late seventeenth century, when the European climate chilled markedly? Luckily, in 2010 normality asserted itself and the sunspot numbers started gradually rising.

The Sun is also fairly quiet in terms of the variation of its energy output. From peak to trough, the variation in total solar flux is only 0.1 percent and no long-term variation has been seen over thirty years. The extreme ultraviolet tail of the dog wags much more: 30 percent within a few weeks and a factor of 2 up to 100 over the whole solar cycle, depending on wavelength.36 This has important implications for our understanding of the Earth’s cli­mate, since human-i nduced change must be distinguished from natural variations in solar output.

Perhaps one reason the Sun is so equable is the fact that it steadily snacks on comets. One of the surprises of the SOHO mis­sion has been its prowess as a comet-hunter; the trawl is already well over two thousand. The Large Angle and Spectrometric Coro – nograph blocks the Sun’s face with an occulting disk, creating an artificial eclipse (figure 7.3). Most of the comets are “sun-grazers” that fly like Icarus very close to the Sun and then grow tails as their icy cores are heated. Toni Scarmato, a high school teacher from Calabria in Italy, discovered the one-thousandth comet in 2006, and two-thirds of them have been found by scouring coronograph data just after it’s taken and put on the web.37 SOHO found its two-thousandth comet in late 2010 and it has discovered half of

the comets for which orbits have been measured since 1761. The dance of fire and ice has become a way that the public has em­braced this protean space mission.