Guest post by Paul Dorian
The sun continues to be very quiet and it has been without sunspots this year 70% of the time as we approach what is likely to be one of the deepest solar minimums in a long, long time. In fact, all indications are that the upcoming solar minimum may be even quieter than the last one which was the deepest in nearly a century. In addition, there are now forecasts that the next solar cycle, #25, will be the weakest in more than 200 years. Even weak solar cycles, however, can produce significant solar storms. In fact, it was this same time of year back in 1859 when a super solar storm – now known as the “Carrington Event” – took place during another weak solar cycle (#10). The event has been named for the British astronomer, Richard Carrington, as he observed from his own private observatory the largest solar flare which caused a major coronal mass ejection (CME) to travel directly toward Earth. Fortunately, solar storms of this magnitude are quite rare as it would very likely have a much more damaging impact on today’s world than it did in the 19th century.
The solar storm of September 1, 1859
This past weekend saw the strongest geomagnetic storm of the year with northern lights visible all the way down into the northern US, but it was nothing in comparison to what took place 160 years ago. From August 28, 1859 to September 1, 1859 numerous sunspots and solar flares were observed on the sun and auroras were being observed in different parts of the world. Just before noon on the cloudless morning of Thursday, September 1, 1859, 33-year-old astronomer Richard Carrington – widely acknowledged at the time to be England’s best – was in his own private observatory and, as he usually did on sunny days, he used his telescope to project an 11-inch wide image of the sun on a screen and carefully drew the sunspots that he saw. Suddenly, two brilliant beads of blinding white light appeared over the sunspots, intensified rapidly, and became kidney-shaped. He realized that he was witnessing something unprecedented and left for about one minute to find another witness. On returning within 60 seconds, he and his witness found that much had already subsided in that short time.
The next morning, Friday, September 2nd, 1859, when the CME arrived, it crashed into Earth’s magnetic field, causing the global bubble of magnetism that surrounds our planet to shake and quiver. The CME reached the Earth some 17.6 hours after the eruption which is much quicker than the normal journey time of 3 or 4 days as an earlier CME actually cleared the way of the ambient solar plasma for the second blast to move so quickly. Rapidly moving fields induced enormous electric currents that surged through telegraph lines and disrupted communications. In fact, telegraph systems all over Europe and North America went haywire and, in some cases, telegraph operators were literally shocked as sparks were flying and telegraph paper was often set on fire. Some systems actually continued to work despite being disconnected from their power supplies as aurora-induced electric currents still allowed messages to be transmitted. Skies all over Earth erupted in red, green and purple auroras – even in tropical locations like Cuba, Jamaica, El Salvador, the Bahamas and Hawaii. The auroras were so bright over the Rocky Mountains that their glow awoke gold miners who began preparing breakfast because they thought it was morning. People in the northeastern US could read a newspaper by the aurora’s light.
On Saturday, September 3, 1859, the Baltimore American and Commercial Advertiser reported, “Those who happened to be out late on Thursday night had an opportunity of witnessing another magnificent display of the auroral lights. The phenomenon was very similar to the display on Sunday night, though at times the light was, if possible, more brilliant, and the prismatic hues more varied and gorgeous. The light appeared to cover the whole firmament, apparently like a luminous cloud, through which the stars of the larger magnitude indistinctly shone. The light was greater than that of the moon at its full, but had an indescribable softness and delicacy that seemed to envelop everything upon which it rested. Between 12 and 1 o’clock, when the display was at its full brilliancy, the quiet streets of the city resting under this strange light, presented a beautiful as well as singular appearance.”
Today’s view of “The Carrington Event”
Back in the 19th century there were no X-ray satellites or radio telescopes and no one knew solar flares existed until that September morning. “What Carrington saw was a white-light solar flare—a magnetic explosion on the sun,” explains David Hathaway, solar physics team lead at NASA’s Marshall Space Flight Center in Huntsville, Alabama. “It’s rare that one can actually see the brightening of the solar surface,” says Hathaway. “It takes a lot of energy to heat up the surface of the sun!” The explosion witnessed by Carrington produced not only a surge of visible light, but also a mammoth cloud of charged particles and detached magnetic loops—a “CME”—and hurled that cloud directly toward Earth. “In the 160-year record of geomagnetic storms, the Carrington event is the biggest”, says Hathaway. In fact, going back farther in time by examining Arctic ice (energetic particles leave a record in nitrates in ice cores), it is estimated that this event may have been the biggest in 500 years and nearly twice as big as the runner-up.
Impact on today’s world
Today we know that solar flares happen frequently, especially during solar sunspot maximums. In today’s world, electronic technologies have become embedded into everyday life and are, of course, quite vulnerable to solar activity. Power lines, long-distance telephone cables, radar, cell phones, GPS, and satellites – all could be significantly affected by an event like this one. In other words, the world’s high-tech infrastructure could grind to a halt disrupting daily activities from purchasing a gallon gas to using the Internet.
Of particular concern is the fear about what this kind of solar storm could do to the electrical grid since power surges caused by solar particles can blow out giant transformers. If numerous transformers happened to be destroyed at once, it would likely take a painfully long time to replace them. The eastern US is especially vulnerable since the power infrastructure is highly interconnected so that failures in one location could cause failures in other regions. One long-term solution to this vulnerability would be to rebuild the aging power grid to be less susceptible to solar disruptions.
On the positive side, there is comfort in the fact that observations of the sun in today’s world are a constant with a fleet of spacecraft in position to monitor the sun and gather data on solar flares. Also, there is better forecasting in today’s world and solar scientists could give some sort of warning as to when solar flares might appear and whether a given storm is pointed at Earth. Improved forecasting can allow for mitigating actions to be taken since the most damaging emissions travel slowly enough to be detected by satellites well before the particles strike the Earth. For example, power companies could protect valuable transformers by taking them offline before a solar storm strikes. Finally, statistics suggest that “Carrington-type” flares are perhaps once in a half-millennium events. The statistics are far from solid, however, and Hathaway (NASA) cautions that we don’t understand flares well enough to rule out a repeat in our lifetime.
Meteorologist Paul Dorian