In addition to hot gas, the sun's surface is also penetrated by magnetic fields, as is the Earth's surface although the Earth's magnetic field is not nearly as strong. In places, the solar magnetic field is stronger than in others and, in some of these places, the magnetic field lines of force can become twisted, which is a way of storing energy. Think of a rubber band-driven airplane; we can hold the airplane steady while twisting a rubber band around and around.
As we twist the rubber band, we are storing energy, and when we let go of the propeller, that stored energy causes the propeller to turn quickly enough to let the plane take off.
In an analogous manner, the twisted solar magnetic fields store energy and, when that energy is released, it sprays huge amounts of hot gas into space. This is a solar flare. The particles emitted during a solar flare are high-energy hydrogen and helium atoms that have had all of their electrons removed. But alpha radiation is high-energy helium nuclei and hydrogen nuclei are simply protons.
Both of these are forms of radiation, as are the electrons beta radiation and neutrons found within the gas. In other words, a solar flare is a huge emission of radiation from the sun, and if it's aimed at the Earth, we will experience higher levels of radiation because of this. In the wake of a Carrington-like event today, entire power grids could shut down and GPS satellites could be knocked offline. While working in his observatory, Richard Carrington saw two brilliant points of light emerge from among a clutch of dark sunspots and vanish within five minutes.
Another English astronomer, Richard Hodgson, saw the same thing, noting that it was as if the brilliant star Vega had appeared on the Sun. Before then, no one knew about solar flares — mostly because no one was tracking sunspots every clear day the way Carrington was.
Decades would pass before astronomers and physicists could unravel the physics of solar flares and their impact on Earth. A solar flare is an eruption on the Sun, a sudden flash of light — usually near a sunspot — that can release as much energy as roughly 10 billion 1-megaton nuclear bombs. The trigger is a sudden, localized release of pent-up magnetic energy that blasts out radiation across the entire electromagnetic spectrum, from radio waves to gamma rays. Most solar eruptions miss our planet by a wide margin.
But occasionally, one gets aimed right at Earth. About eight minutes after a solar flare, its light reaches Earth in a flash of visible light. That was the twitch the magnetic instruments at the Kew sensed in The coronal mass ejection can trigger a geomagnetic storm when it encounters the magnetic field that envelops Earth.
The disturbance to the magnetic field induces electrical currents to course through conductors, including wires and even the planet itself. At the same time, high-speed charged particles spewed by the sun crash into atoms in the upper atmosphere, lighting up the aurora.
On September 6, , the sun emitted a powerful X-class solar flare — a designation reserved for the most intense flares. The flare has long been, and remains, a standout in its energy and effects on Earth. In May , the Sun dealt our planet a geomagnetic storm on par with the Carrington Event. As in , a brilliant aurora appeared well beyond the polar regions. Telegraph and telephone systems broke down, with some sparking destructive fires.
And just 13 years after Carrington spied his eponymous flare, another solar storm came along that by some measures may have topped it. If anything, the Sun has been holding back in the modern era. Evidence from the more distant past points to a few solar storms that make the Carrington Event seem almost puny by comparison. Trees have long memories. Each year of growth chronicles tidbits about environmental conditions at the time in concentric annual rings. Some cedar trees in Japan recall a tsunami of atomic particles hurled from the Sun around the year Those trees recorded a significant uptick in carbon, a radioactive variant of carbon that trees absorb from the atmosphere.
Carbon emerges from run-ins between atmospheric nitrogen and cosmic rays — high-speed particles from space that pummel our planet daily. Some solar flares shower Earth with an excess of cosmic rays, which ramps up production of carbon The change in carbon levels recorded in was about 20 times larger than the normal ebb and flow from the Sun, researchers reported in A carbon boost in tree rings showed signs of another sizable solar event in Ice cores from Antarctica showed a corresponding increase, in both and , of beryllium, another product of cosmic rays — adding more certainty to the tree ring findings.
Looking farther back in time, a study of ice cores suggests a third similar event around BCE. And in August in a paper still undergoing peer review , researchers reported two more carbon spikes in tree rings from around BCE and BCE, possibly on par with the event.
These shock waves can accelerate charged particles ahead of them — causing increased radiation storm potential or intensity. Important CME parameters used in analysis are size, speed, and direction. This can often provide 15 to 60 minutes advanced warning of shock arrival at Earth — and any possible sudden impulse or sudden storm commencement; as registered by Earth-based magnetometers.
Important aspects of an arriving CME and its likelihood for causing more intense geomagnetic storming include the strength and direction of the IMF beginning with shock arrival, followed by arrival and passage of the plasma cloud and frozen-in-flux magnetic field. More intense levels of geomagnetic storming are favored when the CME enhanced IMF becomes more pronounced and prolonged in a south-directed orientation.
Some CMEs show predominantly one direction of the magnetic field during its passage, while most exhibit changing field directions as the CME passes over Earth. CMEs are pretty rare, but there are almost always smaller amounts of energetic particles that come with a solar flare.
The speed of the particles depends on the strength and rapidity of the flare that sends them flying. The highest energy particles from a flare can arrive in as little as two minutes after the electromagnetic radiation, while CMEs take up to three or four days to arrive at Earth.
Even though solar flares are highly energetic, the Earth has built-in protective mechanisms. Most dangerous electromagnetic radiation is absorbed by the atmosphere, and the high-energy particles are trapped and diverted by the Earth's magnetic field. The far northern or southern latitudes are the most susceptible to possible damage, and the last event of any importance was in , when a large solar flare shut down service to 6 million people for up to nine hours in Quebec, Canada.
Power Grid," concluded that a major solar event has the potential to damage the electrical grid catastrophically, and made recommendations for "hardening" electrical facilities to withstand a powerful magnetic storm. The National Association of Regulatory Utility Commissioners, in a report, said models predict a 50 percent chance that a catastrophically large solar flare would occur "within several decades.
0コメント