Space Weather is something that has probably never crossed the minds of most people in the world. For the sliver of the population that has actually heard of it, space weather may still come across as a rather mysterious concept. And why shouldn’t it seem weird? Space weather encompasses a variety of thoroughly unfamiliar phenomena, and, unless you have had the fortune to observe the shimmering of the aurora in the night’s sky at the polar extremes of our planet, humans have no direct experience with the various happenings beyond the sky.
Of course, if you had been living your entire life in an enclosed room with neither windows, nor exits, nor the internet, stepping outside to find water falling on you from the sky would be awfully puzzling, too. The weather on Earth has many different manifestations—rain, hail, snow, thunder, lightning, tornados, hurricanes, floods, and so much more—and it would be very confusing to try to make sense of it all if we did not have a lifetime of experience to breed our familiarity with the weather. Of course, even with Earth’s weather, there are rare moments that can still surprise a forty-year old adult—like the first time I saw thundersnow on a chilly winter night in Iowa, or caught the sight of a desert rainstorm off in the distance where the raindrops evaporated before they hit the ground, a phenomenon known as virga. But the first time someone hears about all of the various aspects of space weather, it is all very new and sounds fantastic, and it may be difficult to make sense of it all.
Did You Say Ejection?
To make matters worse, space weather is often described in nearly indecipherable scientific jargon, making it hard for normal people to make heads or tails of what is being said (as opposed to scientists, who, it could be argued, are not exactly normal people.) For example, one of the most threatening occurrences in space weather is the coronal mass ejection, too often whittled down to just CME. This sounds like a serious medical condition, or perhaps an embarrassing night’s sleep for a teenage boy. It does not convey, to the common man or woman, a billion tons of electrified gas and magnetic fields hurtling towards the Earth at five million miles per hour. A much more evocative term, in my estimation, is a magnetic tsunami. My aim in Partly Cloudy with a Slight Chance of X-Rays: Space Weather Explained is to explain everything about space weather in terms that you can understand.
I am quite convinced that my having the audacity to introduce some new terms to describe the varied aspects of space weather will make many a professional space physicist cringe. But, to communicate scientific ideas to non-scientists using language that people can understand is important. Although technical terms convey a precise meaning to scientists, to regular people they often express much less. Scientists may protest loudly about my creating new terminology, but I will consciously sacrifice scientific precision to the evocative power of the English language, because this blog is not for scientists, but instead for everyone else. Below I will define these newly coined terms and explain my reasons for favoring them over the more technically precise standards. In addition, at the top of this blog, there is a glossary containing all of the terms (standard and new) that I have chosen to use, including their definitions and translations to more technically precise terms.
What Happens at the Sun Does Not Always Stay at the Sun
Everyone can appreciate the spectacular beauty of the aurora, but the aurora is really the final step in a long chain of events that starts at the sun. My goal is to convey the fascinating details of the entire process, so that everyone, not just scientists, can understand and appreciate, not only a dazzling auroral display, but all of the magnificent but invisible events leading up to it.
To put the menagerie of space weather effects into some semblance of order, it is helpful to make clear the separation between two concepts: first, the primary drivers of space weather that emerge from the sun; and, second, the impact that those drivers have on the Earth and its protective magnetic field. The sun directly controls space weather by launching mass and energy out into space towards the Earth. There are three distinct ways in which this occurs, corresponding to three of the key phenomena of space weather: solar flares, proton hailstorms, and magnetic tsunamis.
Solar flares blast the solar system with energy in the form of electromagnetic waves. Visible light is part of the spectrum of electromagnetic waves (corresponding to a wavelength of a few hundred nanometers)—a bright solar flare indeed sends out a flash of visible light. But the bulk of the energy in particularly strong solar flares emerges in the form of x-rays, electromagnetic waves of much shorter wavelength (less than ten nanometers) that carry a lot of energy.
Solar Flare: An x-ray image of the sun, showing the intensely blinding x-rays from a class X7 solar flare. Credit: NASA.
Proton hailstorms occur when violent activity on the sun spews out very high energy particles (primarily protons, but also electrons and heavier elements, such helium, oxygen, and iron). The protons zip towards the Earth at about one third of the speed of light, or around 200 million miles per hour. It takes light about 8 minutes to travel from the sun to the Earth at light speed (670 million miles per hour), so a proton hailstorm reaches the Earth in about 30 minutes, with the storm lasting from hours to days. A solar energetic particle event is the technical term used by scientists to describe this type of space weather, and fast particles are commonly denoted with the abbreviation SEPs, a bland term that conveys little to the non-scientists.
The Space Weather Prediction Center of the National Oceanic and Atmospheric Administration (NOAA) uses the slightly more descriptive term solar radiation storm, rating the severity of these storms on a scale from S1 to S5. But the rather vague term radiation is often highly misunderstood by the general population, typically evoking thoughts of the Cold War, or of a horribly painful death. As a technical term, radiation is so broadly defined that it can mean high-energy light waves called gamma rays (even shorter wavelength, and thus higher energy, than x-rays) or highly energetic particles, such as electrons or helium nuclei (also known as alpha particles). Most people don’t know that radiation is either some form of electromagnetic wave or a shower of fast particles. Both of these forms are microscopic and energetic, and can damage materials and living flesh (by damaging DNA and other biological components of your body at an atomic level). Because the cause of this harm is invisible, without scientific instruments it is not possible to determine whether waves or energetic particles are responsible, so the catch-all term radiation is used. I find that term radiation is not very telling about what is actually occurring, so I prefer the new term proton hailstorm, believing it to be far more illustrative than solar energetic particle event or solar radiation storm.
Proton Hailstorm: A artist’s conception of a proton hailstorm inundating an Earth-orbiting satellite at five million miles per hour. Credit: European Space Agency (ESA).
The third type of space weather that can hurl both mass and energy toward the Earth is the magnetic tsunami. The sun is made up of gas, primarily hydrogen, with some helium and a very tiny amount of heavier elements such as carbon, nitrogen, and oxygen. This gas is so hot that it undergoes ionization, stripping electrons from the neutral atoms or molecules. The resulting morass of ions and electrons is known as a plasma, the fourth state of matter. Because plasmas are made up of charged particles, not only do they respond to the pressure forces that control the behavior of ordinary environments such as the air and water on Earth, but also they react to electric and magnetic fields. Particularly ferocious events on the surface of the sun can cause an explosion that hurls a massive cloud of magnetized plasma into space, leading to a magnetic tsunami plowing its way through the solar system at five million miles per hour. A severe magnetic tsunami may contain billions of tons of plasma with remnants of the sun’s magnetic field embedded inside. This event is much like a volcanic eruption on Earth that spews hot gas and dust into the air, but this eruption actually escapes the sun altogether, flying out into distant space. The scientific term for this occurrence is a coronal mass ejection, or CME, jargon that I find lacks any illustrative character.
Magnetic Tsunami: Observations from NASA’s SOlar and Heliospheric Observatory (SOHO) showing a magnetic tsunami erupting from the sun on February 27, 2000. Credit: NASA.
What Happens Next?
When the sun throws a tantrum, it hurls light waves, particles, and magnetized plasma towards the Earth in the form of solar flares, proton hailstorms, and magnetic tsunamis. The situation becomes infinitely more complex when this barrage of mass and energy hits the Earth, impacting its protective magnetic field, and leading to an often confusing array of occurrences that comprises the rest of what we call space weather. Next time, we will place these effects on the Earth into the more familiar context of the weather that we experience on the Earth every day.