by Jerry Emanuelson, B.S.E.E.
Unfortunately, before beginning to write about the effects of solar storms on human civilization, I have to undo a lot of myths. This is especially difficult right now because articles in the popular media are generating new myths at an astounding rate. At the time of this writing, the biggest myth being generated is the idea that solar flares can damage the electric grid on the surface of the Earth. This is completely wrong. Solar activity does pose an extremely serious threat to the power grid, but blaming the threat on "solar flares" is just very careless writing, and it reflects a lack of understanding of different types of space weather.
Basically, there are three entirely separate space weather phenomena that everyone needs to understand. Although they often occur together, each can occur separately, without the other two. These 3 phenomenona are:
There is also a separate phenomenon called a solar radiation storm. Solar radiation storms usually consist mostly of highly energetic protons and are often called a proton storm. Protons have mass, and although it is sometimes considered a form of coronal mass ejection, a solar radiation storm travels outward from the sun at a significant fraction of the speed of light. So a solar radiation storm can reach the Earth in as little as 30 minutes, where more common coronal mass ejections take at least 17 hours to reach the Earth.
The two that are most often confused are solar flares and coronal mass ejections. Here is an excellent video from the NASA Goddard Spaceflight Center explaining the difference:
More information on the difference between solar flares and coronal mass ejections can be found at this NASA Goddard web page.
Geomagnetic storms are what can cause severe disturbances of the power grid. Extremely severe geomagnetic storms can cause large-scale destruction of the power grids of the Earth, especially to the large transformers in the transmission system.
The strongest geomagnetic storms usually result from a coronal mass ejection (CME) hitting the Earth. CMEs have a magnetic field. When the CME has a magnetic field with a polarity of "north" (in other words, the same as the Earth's magnetic field), then the geomagnetic field will tend to repel the CME since like magnetic poles repel each other. If the CME arrives with a "south" polarity (in other words, opposite to the Earth's magnetic field), then the geomagnetic field will tend to attract the CME and the resulting geomagnetic storm can be quite strong.
Solar radiation storms can also cause significant geomagnetic storms on the Earth.
Geomagnetic storms can happen for other reasons that do not involve a CME or a solar radiation storm. Geomagnetic storms from these other causes are usually not damaging, although they can be strong enough to produce brilliant auroral displays at high latitudes. One reason for those geomagnetic storms is changes in the solar wind.
NASA's glossary describes the solar wind this way: "A continuous stream of charged solar particles (mainly hydrogen ions) and magnetic fields from the Sun. This continuous stream of ionized gas, or plasma, expands into interplanetary space from the Sun's corona. After escaping from the gravitational field of the sun, this gas flows outward at a typical speed of 400 kilometers per second to distances known to be beyond the orbit of Pluto."
Much of the time, the solar wind passes the Earth at a fairly constant rate. Occasional "gusts" in the solar wind or sudden rotations in the magnetic field of the solar wind can cause geomagnetic storms on the Earth. These geomagnetic storms caused by variation in the solar wind are usually not severe.
Although solar flares and coronal mass ejections often occur together, sometimes a large solar flare will not cause a coronal mass ejection. Coronal mass ejections can also come from magnetic disconnections on the sun that do not involve a solar flare.
In human recorded history, though, the largest coronal mass ejections have occurred along with a solar flare. The most famous such event was the Carrington Event of 1859. This is often considered as the reference event against which all other space weather is measured. In 1859, astronomers observed the solar flares directly (there were more than one) and the impact of the resulting geomagnetic storm was recorded in newspapers around the world.
There is accumulating evidence, though, that solar activity in the past has impacted the Earth (more than 1200 years ago) that were about 20 times larger than the 1859 Carrington Event. Recent studies of other stars (that are very similar to our Sun) indicate that stellar flares of 100 to 1000 times the energy of the Carrington Event have happened on those stars and are possible on our own Sun.
I will discuss the evidence for geomagnetic storms far larger than the Carrington Event of 1859 when this page is finished. This current page is only a first draft.