The Solar Storm of 1921

The biggest of the 20th century

If you've found this site, you're likely familiar with the Carrington event - a major solor storm in September 1859. The first clear record of a solar flare, it led to the most intense geomagnetic storm since people could objectively measure such things. Auroras were seen across the world, including much closer to the equator than other significant storms. Telegraph systems throughout Europe and North America were disrupted, and you can find a lot of speculation about the impact a similar event would have on our power grid and technology-reliant society.

Have a look at the magnetic field created by a bar magnet. Then look at images or video of the sun in certain wavelengths.

The sun has powerful magnetic fields that store energy. We're able to see those fields because charged particles spiral around magnetic field lines.[a]See [a] below.

That energy can be suddenly unleashed, forcing charged particles through the solar system, sometimes toward earth.

When those particles interact with the earth's magnetic field, they both spiral around the earth's field lines, and distort the earth's field. And the act of changing a magnetic field creates an electric field [b]See [b] below.. If there are any conducting materials around, this produces a voltage that will affect circuits connected to them.

A charged particle through a magnetic field experiences a force given by F→B = qv→ × B→ where F→B is the magnetic force on the particle with charge q moving with velocity v→ through the magnetic field B→.

This uses the right hand rule for cross products, which requires you to think three-dimensionally.

Combine that with ΣF→ = ma→ and a bit of first-semester physics, and you can see why the particles spiral around the magnetic field.

A changing magnetic field creates a voltage across a single conducting loop (such as a connection from overhead wires, through a telegraph station, to the ground, to the other end of the overhead wires) according to V = -d/dt{BA cosθ} where the voltage produced V depends on how quickly there are changes in: the magnetic field B caused by something other than the wires themselves (in this case, the earth's magnetic field), the area A that field passes through, and/or the angle θ between the magnetic field and the "normal"[*]From the Latin norma for "carpenter's square" which carpenters use to make sure things are perpendicular. Never call it the "natural line" or "usual line" - it has a totally different meaning. I teach my students to build an autocorrect function into their brains: "normal" → "perpendicular". to the area.

In the case of telegraph wires connected to two stations and the ground, the area is very large [*](several kilometers/miles of cable, several meters/yards above the ground), so you might think this voltage would usually be large. But most of the time, the earth's magnetic field changes strength and direction so incredibly slowly that this voltage is not worth bothering with.

However, during a solar storm, the charged particles from the sun can cause the earth's magnetic field to change strength and direction rapidly enough that this voltage can create sparks. So, wires themselves don't catch on fire - but flammable things near the wires can be ignited by the sparks.

(The strong solar storms in May 2024 have only added to the interest in the Sun.)

But did you know about the solar "magnetic superstorm" of May 1921, which produced fires in switchboards and telegraph exchanges in Europe and North America? Its intensity was similar to that of the Carrington event.

Interestingly, it was not driven by a single powerful flare, but by "a series of interplanetary coronal mass ejections" (including an especially powerful one). The earlier activity "may have cleared much density from the inner heliosphere, enabling a subsequent CME to travel quickly to Earth and cause intense activity."

Read more about it at:

Interestingly, 1921 also saw an extreme drought in Europe, and high temperatures across the United States (especially in October). The dry conditions started well before these solar storms, so there is not an obvious direct link. But could they have made it worse?

It's not out of the question. There's a rather well-established connection between solar activity, cosmic rays, and cloud cover. And perhaps interplanetary dust and debris was swept out of the way. Since it appears 5200 tons of space dust falls on Earth each year, those could help nucleate droplets in clouds, or have other effects.

The solar storms in May 2024 also came from a sunspot group sending many flares, both toward earth, and in other directions (including those the earth will be headed toward in the coming months).

Will there be similar hot and dry conditions as a result? Time will tell.