|
Coronal Mass Ejections Can Cause Grid Failure
A coronal mass ejection (CME) is an ejection of material from the solar corona. They occur when a large bubble of plasma escapes the sun's gravitational field and travels through space to the earth at high speeds over the course of several hours. The ejected plasma consists primarily of electrons and protons (in addition to small quantities of heavier elements such as helium, oxygen, and iron), plus the entraining coronal magnetic field. Plasma is essentially electrically charged (ionized) gas, consisting of free-moving electrons and ions (atoms that have lost electrons). On earth, we are familiar with the ordinary states of matter: solids, liquids and gases. But in the universe at large, plasma is by far the most common form. Plasma in the stars and the space between them makes up 99 percent of the visible universe.
The corona (as opposed to "a Corona" - a popular Mexican beer) is the outermost layer of the Sun's atmosphere. It extends millions of kilometers into space, most easily seen during a total solar eclipse, but also observable in a coronagraph. The Latin root of the word corona means crown. Coronal Mass Ejections were once thought to be the result of solar flares, but while they sometimes accompany solar flares, there is no direct relation between the two.
Coronal Mass Ejections are often called "solar storms" or "space storms" in the popular media. Coronal mass ejections cause shock waves in the thin plasma of the heliosphere, launching electromagnetic waves and accelerating particles (mostly protons and electrons) to form showers of ionizing radiation that precede the CME. When a CME impacts the Earth's magnetosphere, it temporarily deforms the Earth's magnetic field, changing the direction of compass needles and inducing large electrical ground currents in Earth itself; this is called a geomagnetic storm and it is a global phenomenon. Coronal Mass Ejections impacts can induce magnetic reconnection in Earth's magnetotail (the midnight side of the magnetosphere); this launches protons and electrons downward toward Earth's atmosphere, where they form the aurora.
A geomagnetic storm is a temporary disturbance of the Earth's magnetosphere caused by solar coronal mass ejections, coronal holes (the fast-moving component of the solar wind is known to travel along open magnetic field lines that pass through coronal holes), or solar flares. A geomagnetic storm is caused by a solar wind shock wave which typically strikes the Earth's magnetic field 24 to 36 hours after the event. This only happens if the shock wave travels in a direction toward Earth. The solar wind pressure on the magnetosphere will increase or decrease depending on the Sun's activity. These solar wind pressure changes modify the electric currents in the ionosphere. Magnetic storms usually last 24 to 48 hours, but some may last for many days.
From August 28 until September 2, 1859, numerous sunspots and solar flares were observed on the sun, the largest flare occurring on September 1st. A massive coronal mass ejection headed directly at Earth due to the solar flare and made it within eighteen hours — a trip that normally takes three to four days. On September 1 – 2, the largest recorded geomagnetic storm occurred, as recorded by the Colaba observatory near Bombay, India. There are records in Boston that the light was so bright that even at 1:00 AM it was possible to read a newspaper without any other source of light. The combination of the Solar Flare and Coronal Mass Ejection caused a geomagnetic storm that created strong enough currents in certain long Telegraph (then about 15 years old) wires in both the United States and Europe experienced induced emf, in some cases even shocking telegraph operators and causing fires. Auroras were seen as far south as Hawaii, Mexico, Cuba, and Italy - phenomena usually only seen near the poles. This was the 1859 solar superstorm. On March 13, 1989 a severe geomagnetic storm caused the collapse of the Hydro-Québec power grid in a matter of seconds as equipment protection relays tripped in a cascading sequence of events. Six million people were left without power for nine hours, with significant economic loss. The storm even caused auroras as far south as Texas. The geomagnetic storm causing this event was itself the result of a coronal mass ejection, ejected from the Sun on March 9, 1989. In August 1989, another storm affected microchips, leading to a halt of all trading on Toronto's stock market. Since 1989, power companies in North America, the UK, Northern Europe and elsewhere evaluated the risks of geomagnetically induced currents (GIC) and developed mitigation strategies. Since 1995, geomagnetic storms and solar flares have been monitored from the Solar and Heliospheric Observatory (SOHO) joint-NASA-European Space Agency satellite. On February 26, 2008 the magnetic fields erupted inside the magnetotail, releasing about 1015 Joules of energy. The blast launched two gigantic clouds of protons and electrons, one toward Earth and one away from Earth. The Earth-directed cloud crashed into the planet below, sparking vivid auroras in Canada and Alaska.
When magnetic fields move about in the vicinity of a conductor such as a wire, a geomagnetically induced current is produced in the conductor. This happens on a grand scale during geomagnetic storms (the same mechanism also influences telephone / telegraph lines and above ground piping (think the Alaskan pipeline)) on all long transmission lines. Fiber optic lines and underground cables are not affected. Power companies, which operate long transmission lines (many kilometers in length), are thus subject to damage by this effect. Notably, this chiefly includes operators in China, North America, and Australia; the European grid consists mainly of shorter transmission cables, which are less vulnerable to damage. The (nearly direct) currents induced in these lines from geomagnetic storms are harmful to electrical transmission equipment, especially generators and transformers — since they induce core saturation, constraining their performance (as well as tripping various safety devices), and causes coils and cores to heat up. This heat can disable or destroy them, even inducing a chain reaction that can blow transformers throughout a system. This is precisely what happened on March 13, 1989: in Québec, as well as across parts of the northeastern U.S., the electrical supply was cut off to over 6 million people for 9 hours due to a huge geomagnetic storm. Some areas of Sweden were similarly affected. According to a study by MetaTech Corporation: if a storm with a strength comparative to that of 1859 were to strike today, up to 350 transformers would be broken and 130 million people would be left without power in the US. It could take 4 to 10 years and more than a trillion dollars to repair the damage.
By receiving geomagnetic storm alerts and warnings (e.g. by the Space Weather prediction Center; via Space Weather satellites such as SOHO or ACE), power companies can (and often do) minimize damage to power transmission equipment, by momentarily disconnecting transformers or by inducing temporary blackouts. ACE orbits the L1 libration point which is a point of Earth-Sun gravitational equilibrium about 1.5 million km from Earth and 148.5 million km from the Sun. From its location at L1, ACE has a prime view of the solar wind, interplanetary magnetic field and higher energy particles accelerated by the Sun, as well as particles accelerated in the heliosphere and the galactic regions beyond. ACE also provides near-real-time 24/7 continuous coverage of solar wind parameters and solar energetic particle intensities (space weather). When reporting space weather ACE provides an advance warning (about one hour) of geomagnetic storms that can overload power grids, disrupt communications on Earth, and present a hazard to astronauts. The spacecraft has enough propellant on board to maintain an orbit at L1 until ~2024. ACE provides about 15 to 45 minutes of heads-up to power plant operators if something’s coming in. They can shunt loads, or shut different parts of the grid. But to just shut the grid off and restart it is a $10 billion proposition, and there is lots of resistance to doing so. Many times these storms hit at the north pole, and don’t move south far enough to hit us. It’s a difficult call to make, and false alarms really piss people off. Long term preventative measures also exist to protect against Coronal Mass Ejections, including digging transmission cables into the soil, placing lightning rods on transmission wires, reducing the operating voltages of transformers, and using cables that are shorter than 10 kilometers. It might also be possible to develop and deploy large resistors that would add another level of protection to large transformers. Here is a video about NASA's Video satellite mission to better understand Coronal Mass Ejections.
|