Everyone is familiar with the concept of weather and how it can affect daily activity and change with the seasons. But what is space weather?
According to NASA, “Space weather includes any and all conditions and events on the sun, in the solar wind, in near-Earth space and in our upper atmosphere that can affect space-borne and ground-based technological systems and through these, human life and endeavor.”
As far as humans are concerned, almost all space weather is due to activity on the Sun’s surface. Let’s dig into what space weather is by examining four major phenomena: auroras, solar wind, coronal mass ejections (CMEs) and solar flares. But first, we must discuss how the Earth is protected from these events.
Earth’s Magnetosphere, Ionosphere and Atmosphere
We are protected from most space weather by Earth’s magnetosphere, ionosphere and atmosphere. The Earth’s magnetic field (or magnetosphere) extends far into space and provides the first layer of protection from weather in space. The magnetosphere isn’t actually sphere-shaped but has a shape that’s strongly influenced by the solar wind coming from the sun. Like a long-haired dog enjoying the breeze during a car ride, Earth’s magnetosphere is teardrop-shaped. The side facing the Sun is compressed by the solar wind, while the night side is stretched into a long “magnetotail.” The magnetosphere helps block harmful solar and cosmic radiation.
The next layer of protection is the ionosphere, which contains atoms that interact with high-energy particles from the Sun to form charged ions. In the case of auroras, the ions release energy as light. Closer to the Earth’s surface, the atmosphere blocks harmful ultraviolet radiation.
Let’s take a look at a few examples of space weather, starting with auroras — space weather events you’ve probably seen in photos or videos.
Auroras are colorful, dancing light shows that appear in the night sky at latitudes far from the equator. In the Northern Hemisphere, auroras are known as the Northern Lights or the aurora borealis. In the Southern Hemisphere, they are the Southern Lights or the aurora australis. As National Geographic explains, travelers hoping to see auroras should aim for a magnetic latitude above 55ºC and dark, moonless nights. Auroras can be especially bright around the Spring equinox and the Fall equinox, but there is no guarantee that sky gazers will be lucky enough to see an aurora on any given night. Like many space weather events, auroras are highly unpredictable.
Auroras are emissions of visible light that occur at 60 to 250 miles (100 to 400 kilometers) above the Earth’s surface. They are due to charged particles (electrons) from the Sun colliding with gases in Earth’s upper atmosphere, which is called the ionosphere. An aurora’s colors depend on the molecules involved, as described by NASA. Oxygen molecules produce the more common green-yellow auroras as well as rare red auroras. Nitrogen molecules produce blue auroras.
From 93 million miles (150 million kilometers) away, the sun is constantly spewing gas and particles into space. This material becomes charged as it passes through the Sun’s outer atmosphere (the corona) and streams into space as the solar wind. Like sunlight, the solar wind radiates in all directions, passing through the entire solar system. When the solar wind reaches Earth, it can cause the Earth’s magnetosphere to contract and then expand. These changes can cause electromagnetic disturbances on Earth that are usually mild.
The solar wind is mild and fairly consistent, whereas coronal mass ejections are extreme and unpredictable.
Coronal Mass Ejections (CMEs)
Coronal mass ejections (CMEs) occur when gigantic clouds of magnetized solar particles called plasma erupt from the Sun’s outer atmosphere (the corona). CMEs are the result of powerful solar storms and can cause 100 million tons of plasma to hurl through space at over a million miles per hour. It takes this plasma a few days to reach Earth, where it can cause the magnetosphere to temporarily buckle and create colorful auroras in the ionosphere.
If a CME reaches Earth, it can trigger a geomagnetic storm. The fluctuating magnetic fields associated with these storms can induce current in long electrical wires. These currents can damage electrical equipment, such as transformers, leading to widespread power failures.
A cloud of plasma from a CME can also cause the ionosphere to heat and expand, then cool and contract, which is problematic for satellites that orbit just beyond the ionosphere. Increased friction between a satellite and the atmosphere can drag the satellite into a lower altitude and/or damage it. Both the Hubble Space Telescope and the International Space Station regularly adjust their altitude to remain in orbit.
Magnetic activity within the Sun can cause intense solar storms. During a solar storm, sudden explosions called solar flares can send huge bursts of electromagnetic and particle radiation into space at the speed of light. Electromagnetic radiation includes radio waves, microwaves, infrared light, visible light, ultraviolet (UV) light, X-rays and gamma rays. Particle radiation includes subatomic particles like alpha particles, beta particles, neutrons and positrons. The high-energy UV light, X-rays, gamma rays and particle radiation can be especially damaging.
Solar flares are hard to predict and can reach Earth’s atmosphere just 8.5 minutes after they occur. Most of the energetic particles will be captured by Earth’s magnetosphere, but these high-energy particles can damage spacecraft and satellites used for communication, GPS, imaging, weather and more. Electronic components are especially vulnerable.
During a solar flare, the increase in X-ray radiation causes the ionosphere to absorb high-frequency radio waves instead of reflecting them. The resulting radio blackouts temporarily interfere with communication systems and GPS. Solar flares can also produce CMEs, which reach Earth a few days later.
Historic Geomagnetic Storm
The strongest geomagnetic storm on record is the Carrington Event of September 1859, which caused excess electrical currents to flow through telegraph lines around the world. Telegraph operators were literally shocked, and telegraph equipment and papers caught on fire, as described by History. The Northern Lights were visible as far south as Cuba and Hawaii. The event is named for Richard Carrington, an amateur British astronomer who had observed a solar flare a day or two earlier and noted the coincidence with these worldwide events.
Our reliance on electricity has only increased since 1859. Beyond the electrical devices that people plug in every day, such as refrigerators and medical equipment, essential services like clean water distribution, wastewater treatment, and fuel delivery now require electricity for some steps. When the next Carrington-sized event occurs, it could disable a large portion of the North American power grid, which might take years to recover. Many smaller geomagnetic storms have impacted Earth in the meantime, including one on March 13, 1989 that left six million Canadians without electricity for up to nine hours.
Dangers to Human Health
Humans are at risk of radiation exposure due to weather in space. Doses of high-energy radiation increase with altitude and can lead to radiation sickness and DNA damage that increases the risk of cancer and other diseases. For someone flying in a plane at 25,000 feet, the exposure to radiation is ~10 times higher than at sea level. At 40,000 feet, which is common for commercial aircraft, the exposure is 50 times higher. Astronauts in low orbit on the International Space Station (ISS) receive the radiation equivalent of 5-10 chest X-rays per day, even without any major space weather events. The situation only becomes more hazardous as humans venture further into space. The planet Mars does not generate its own magnetic field, so any humans traveling to Mars will need other means of protection.
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