What Are Geomagnetic Storms? How Do They Impact Earth? Space Weather Analysis

Geomagnetic storms, or "geostorms" for short, are space weather events that occur whenever solar storms fling charged particles directly at Earth, triggering large disturbances in our ionosphere.

Although you may only hear about significant geomantic storms, these space storms are fairly common and occur anywhere from every month or so to every few years.

Formation

Geomagnetic storms form whenever high concentrations of electrically charged particles from solar storms—that is, solar winds, coronal mass ejections (CMEs), or solar flares—interact with Earth's atmosphere.

After travelling the 94-million-mile distance from the Sun to Earth, these particles crash into Earth's magnetosphere—a shield-like magnetic field generated by electrically charged molten iron flowing in Earth's core. Initially, the solar particles are deflected away; but as the particles pushing against the magnetosphere pile up, the buildup of energy eventually accelerates some of the charged particles past the magnetosphere. They then travel along Earth's magnetic field lines, penetrating the atmosphere near the north and south poles.

Geostorm Hazards and Impacts

Ordinarily, the sun's high-energy particles don't travel deeper into our atmosphere than the ionosphere—the section of Earth's thermosphere that sits 37 to 190 miles (60 to 300 kilometers) above ground. As such, the particles pose few direct threats to Earth's living creatures. But for the Earth-based satellite and radio networks residing in the thermosphere (and which we humans depend on, daily), geostorms can be calamitous.

Satellite, Radio, and Communications Disruptions

Radio communication is especially sensitive to geomagnetic storms. Ordinarily, radio waves propagate around the globe by reflecting and refracting off of the ionosphere and back toward earth multiple times. However, during solar storms, the ionosphere (where the sun's extreme ultraviolet and x-ray radiation are largely absorbed) grows denser as the concentration of incoming cosmic particles builds. In turn, this denser layer modifies the transmission path of high-frequency radio signals and can even block it completely.

Similarly, satellites that "live" in the thermosphere and communicate by using radio waves to send signals to antennas on the ground are also at the mercy of geostorms. For example, GPS radio signals travel from a satellite out in space, passing through the ionosphere and to a receiver on the ground. But during geostorms, the ground receiver can't lock onto the satellite signal, and so position information becomes inaccurate. This isn't just true of GPS satellites, but of intelligence gathering and weather forecasting satellites, too.

The stronger the geomagnetic storm, the more severe and long-lasting these disruptions can be. Weak storms might only cause momentary blips in service, but the strongest solar storms can trigger hours-long communications blackouts on Earth.

But What About the Internet?

Since the internet age has coincided with a period of weak solar activity, the effects of geostorms on internet infrastructure aren't well known. However, according to a 2021 study out of the University of California, Irvine, geostorms pose little threat to the worldwide web, largely because the undersea fiber-optic cables that make up the internet's backbone aren't affected by geomagnetically induced currents.

Of course, if a solar storm was massive, say, on the order of the 1859 Carrington and 1921 New York Railroad events, it could damage the signal boosters these cables rely on, essentially breaking the internet.

Power Outages

Geomagnetic storms not only have the power to cut comms, but electricity, too. As the ionosphere is bombarded with extreme ultraviolet and x-ray radiation, more and more of its atoms and molecules are ionized, or gain a net positive or negative electrical charge. These electrical currents aloft then generate an electric field at the earth's surface, which in turn generates geomagnetically induced currents which can flow through ground-based conductors, such as power grids. And when these currents enter electrical transformers and power lines, overloading them with voltage, it's lights out.

Such was the case in 1989, when an intense solar flare downed the entire Hydro-Québec power grid in Quebec, Canada. The blackout lasted for nine hours.

Elevated Radiation Exposure

The more solar radiation that enters our atmosphere during solar storms, the more we humans are exposed to—especially during air travel. That's because the higher your altitude, the less atmosphere there is to shield you from harmful and potentially fatal cosmic radiation—high-energy particles capable of passing into and through objects, including the human body, at the speed of light.

Ordinarily when flying commercial, humans are exposed to 0.035 millisieverts per flight, says the U.S. Centers for Disease Control and Prevention. According to the Health Physics Society, a radiation dose of 0.003 millisieverts per hour is normal (when flying at an altitude of 35,000 feet).

Auroras

One of the few positive side effects of geomagnetic storms is an enhanced viewing of the auroras—the neon green, pink, and blue curtains of light that ignite the sky when charged particles from the sun collide and chemically react with oxygen and nitrogen atoms high in Earth's atmosphere.

These dazzling phenomena are seen nightly above the Arctic (aurora borealis) and Antarctic (aurora australis) regions, thanks to the incessant solar wind, which streams high-energy particles out into space 24 hours a day, seven days a week. On any given day, a number of these stray particles eek their way into Earth's upper atmosphere via the polar regions, where the magnetosphere is thinnest.

But the high concentration of solar particles that bombard Earth during geomagnetic storms allows them to infiltrate more of Earth's atmosphere. This is why some of the strongest solar storms have led to the auroras being seen at lower latitudes—sometimes as far into the mid-latitudes as New York.

A geomagnetic storm's strength also influences aurora color. For example, red auroras, which are rarely seen, are associated with intense solar activity.

Predicting Geomagnetic Storms

Scientists monitor the Sun, like they do terrestrial weather, to try and predict when and where its storms will erupt. While NASA's Heliophysics Division monitor all manner of solar activity via its fleet of more than two dozen automated spacecraft (some of which are positioned at the Sun), it's the responsibility of NOAA's Space Weather Prediction Center (SWPC) to monitor geomagnetic storm activity and keep the public informed about daily Earth-Sun goings-on.

The products and data that the SWPC routinely provides include:

• Current space weather conditions,
• Three-day geostorm forecasts,
• 30-day geostorm forecast outlooks, and
• Aurora sighting forecasts, just to name a few. 

In an effort to convey the threat level to the public, NOAA rates geomagnetic storms on a scale from G1 to G5, similarly to how hurricanes are rated from category one to five on the Saffir-Simpson scale.

The next time you check your city's local weather forecast, don't forget to check your planet's space weather one, too.