Getting Familiar with Space Weather: What Happens at the Earth During a Day of Stormy Weather in Space?

Although they both shine brightly, it turns out that the Sun is nothing like Las Vegas—bad behavior at the Sun does not always stay at the Sun.  When the Sun behaves badly, it hurls light, high energy particles, and tons of magnetized plasma indiscriminately out into the solar system. The different facets of stormy space weather describe what happens when these sporadic outbursts hit the Earth.

On the surface of the sun arise regions of intense activity, solar storms, that can last for months.  In these areas, the intense loops of magnetic field that emerge through the surface of the sun violently thrash about, as seen in the Solar Dynamics Observatory (SDO) image below.  Occasionally two different loops of magnetic field are thrown together with sufficient force to cause them to break and reconnect with the magnetic field of the other loop (the laws of electromagnetism tell us that magnetic field lines can never end, but they can break and immediately connect to a different field line). After this magnetic reconnection, the magnetic field snaps back like a stretched rubber band, releasing a vast amount of magnetic energy as motion of the rebounding plasma.  The change in the magnetic field can release billions of tons of magnetized solar plasma, with some eruptions so ferocious that this magnetic tsunami escapes the gravitational pull of the Sun entirely and barrels out into the solar system.

1-13-15_flare_171-131.jpgSolar Storms and an M-class Solar Flare: An x-ray image of the sun, showing a number of solar storms, area where intense loops of magnetic field violently thrash about.  On the right limb of the sun, an M-class flare is seen erupting from one of these solar storm regions. the intensely blinding x-rays from a class X7 solar flare. Credit: NASA/SDO.

The intense snap back of the magnetic field can also accelerate electrons down towards the Sun’s surface; when those electrons impact the dense plasma of the Sun, they can generate a blinding solar flare. In addition, all of the energy released in an intense solar storm can lead to the acceleration of protons to nearly the speed  of light, showering a section of the solar system in a proton hailstorm. All of these processes drive the space weather that can wreak havoc on critical infrastructure including, the electrical power grid, satellite communications and GPS navigation, and Earth orbiting astronauts and satellites.

What SPF Sunblock Do I Need for This?

The story of stormy weather in space invariably begins with the volatility of the Sun’s magnetic field. Much like the Earth, the magnetic field of sun is generated below its surface by a magnetic dynamo, a process by which internal motions of the plasma that make up the Sun generate powerful magnetic fields.  The surface of the Sun is not solid like the rocky planets that orbit around it, but is more like the surface of a boiling pot of water. Hot plasma from deep down in the Sun rises, and cool plasma at the surface sinks; together these boiling motions effectively move heat, generated by nuclear fusion reactions in the Sun’s core, to the surface where that heat is radiated away as the spectrum of sunlight, like a 6,000 degree Celsius light bulb in the sky.  But embedded in the Sun’s plasma is a magnetic field, and that magnetic field is dragged around and strengthened by these boiling motions. Scientists have yet to understand all of the details of the dynamo process, either in the Sun or in the Earth, but the consequences of the solar dynamo are clear:  the strong magnetic fields generated below the surface by the dynamo become buoyant, causing loops of the magnetic field to rise up through the solar interior and eventually burst through the surface of the Sun. These emerging magnetic fields fill the atmosphere of the Sun, or solar corona, with a chaotic tangle of loops of intense magnetic field.

festooningloops.jpgSolar Storms and an M-class Solar Flare:  Loops of magnetic field seen in the solar corona observed in extreme ultraviolet light. These magnetic fields loops are in constant motion, jostled by the boiling motions of the solar surface below. Credit: NASA/SDO.

This snarl of magnetic fields in the solar corona is not stagnant, but rather these loops are in constant motion, jostled by the boiling motions of the plasma at the surface from which the loops emerged, as pictured above from SDO observations in extreme ultraviolet light. When two loops of magnetic field pointing in different directions are shoved together by all of this frenetic motion, those magnetic field lines can break and reconnect, freeing them to snap back like a stretched rubber band.  Electrons in the tenuous coronal plasma connected to these rebounding magnetic field lines can be catapulted towards the dense plasma at the Sun’s surface. The collisions of these electrons with the Sun’s plasma below can sometimes trigger a brilliant solar flare, blasting the solar system with a deluge of powerful x-rays.

What happens when the intense x-rays from a powerful solar flare reach the Earth?  Fortunately, the Earth’s atmosphere shields the surface of the Earth from the harmful effects of this blast of x-rays, which can damage your DNA at the atomic level, so we don’t need to find a new sunblock with the same SPF (Sun Protection Factor) as block of lead.  But this protection from solar flare x-rays comes at a price for the atmosphere.

When the x-rays from the solar flare bombard the thin air in the Earth’s upper atmosphere, they can tear apart the neutral air molecules, shredding them into their constituent positive ions and freely flying electrons, a process called ionization.  At an altitude of about 40 miles, the neutral upper atmosphere transitions into the ionosphere, where the density of ions and electrons begins increasing with altitude. The resulting surge in the ionization of the upper atmosphere by the x-rays of a solar flare, an ionization storm, can disrupt many of the advanced technologies central to our modern lifestyles.

The primary casualty of a severe ionization storm is communication by radio.  You may think that this is not so bad—poor reception of your local FM radio station during your favorite song is annoying, but hardly a cause to raise alarm.  But radio communications are essential to a broad range of modern technology, from satellite TV to GPS navigation to maintaining safe conditions for the more than 10,000 commercial, private, and military aircraft that may be in the air around the world at any one time.

Proba-V_detecting_aircraft.pngWorldwide Aircraft:  Image of data from the Proba-V mini-satellite operated by the European Space Agency (ESA), showing signals from more the 15,000 separate aircraftCredit: ESA/DLR/SES

Radio waves used for communications from satellites must travel through the ionosphere to reach the Earth, and dramatic jumps in the ionization can interfere with, or even completely cut off, these communications.  Loss of satellite communications may mean more than missing your favorite primetime show on DirecTV—the refraction of radio waves through variations in ionospheric density can lead to errors in GPS triangulation, or the signal could be entirely lost, causing serious problems for the growing number of travelers dependent on GPS for navigation.  During extreme ionization storms, radio communications to aircraft flying efficient polar routes for transcontinental air travel are blacked out completely, requiring re-routing of those flights on longer flight paths. The cascade of delays and increased fuel costs can lead to losses amounting to tens of millions of dollars per year.  Even amateur ham radio operators depend on the ionosphere, bouncing their transmissions off of the ionosphere to reach destinations beyond the local horizon, a phenomenon known as skywave propagation.  Abrupt changes or irregularities in the ionization level can lead to poor reception or even cut off their transmissions entirely.



Skywave Propagation:  Illustration of the bouncing of radio waves off of the ionosphere (red layer) to beat the curvature of the Earth and communicate with locations beyond the local horizon. Credit: Wikipedia/Creative Commons


It’s a Hail of a Day to Be in Space

A blast of x-rays from a powerful solar flare is just the tip of the iceberg of ways in which the sun can cause havoc in space. Although scientists still remain uncertain of how it happens, particularly violent storms on the Sun’s surface can also lead to the acceleration of protons, as well as electrons and heavier ions such as helium, to around 200 million miles per hour, about 1/3 of the speed of light.  Like the shot from a sawed-off solar shotgun, these protons blast out through a section of the solar system, woe to anyone or anything in its way, reaching the Earth in just twenty-four minutes.

Proton hailstorms are a serious hazard for astronauts orbiting the Earth, such as those residing on the international space station, and quick action is necessary to take shelter.  Since the fastest that information can travel is the speed of light, if a violent solar storm on the Sun’s surface triggers a proton hailstorm, it takes eight minutes for the light that typically accompanies the blast of protons to reach the astronauts.  That leaves just sixteen more minutes for the astronauts to reach a sheltered room of the space station before the barrage of protons arrives. If an astronaut is out on a spacewalk at the time, sixteen minutes may indeed not be enough time to return to the safety of the station.

This inherently short warning time for proton hailstorms is why one of the primary missions of the U.S. government’s Space Weather Prediction Center, run by the National Oceanographic and Atmospheric Administration (NOAA), is to generate predictions about space weather conditions.  Only during an all-clear period, when there is no imminent threat of a solar storm that might spark a proton hailstorm or other inclement space weather, will tasks be undertaken requiring astronauts to leave the relative safety of the space station.  If an astronaut were to be caught outside, this bombardment of protons would pass right through the spacesuit, damaging her DNA at an atomic level—if not instantly killing her, this massive dose of high energy protons would almost certainly prove fatal in the short term.

But human beings, with their the delicate biology, are not the only victims that may suffer casualties from a severe proton hailstorm. The sensitive electronics at the heart of communications satellites can also be damaged by the energetic protons and other particles arising from proton hailstorms. In addition, the high energy protons and electrons trapped in the Earth’sVan Allen Radiation Belts, which can be dramatically boosted during periods of severe space weather, can also harm spacecraft circuitry. Spacecraft anomalies, as they are so quaintly called, can be caused by proton hailstorms, and can lead to anything from minor performance glitches to the total loss of a $200 million satellite.

SpaceWeather_SEP_Satellite_ESA.jpgProton Hailstorm Damaging a Satellite:  Artist’s rendition of a proton hailstorm impacting a satellite, causing damage to the spacecraft electronics Credit: ESA.

Proton hailstorms also present a major complication for any future attempt for astronauts to reach Mars, or any other planet in our solar system. Ingenuity is essential to keep the launch mass to a minimum, while still providing the shielding necessary to safeguard the lives of any interplanetary explorers in the face of an intense proton hailstorm.

Here Comes the Big One

Although solar flares and proton hailstorms indeed can impact our technology and cause hundreds of million of dollars in damage to our technological infrastructure, the true behemoth of space weather is the magnetic tsunami. Particularly intense solar storms on the surface of the Sun can sometimes trigger the eruption of a huge mass of plasma and magnetic fields that steamrolls its way straight from the Sun and out through the solar system at up to five million miles per hour.  If the Earth happens to be in the path of this colossus, it’s impact on the protective magnetic field of the Earth can set off a magnetic storm.

cme-graphic_full.jpgMagnetic Tsunami:  Artist’s depiction of a magnetic tsunami that has erupted from a storm on the solar surface and is barreling out into the solar system. Credit: NASA.

The crush of this fast-moving ball of plasma, which can total several billion tons, can compress the Earth’s magnetic field, often tearing into this magnetic shield and dumping a tremendous number of ions and electrons from the Sun directly into the the Earth’s magnetosphere. The injected ions begin circulating westward around the Earth at about 25,000 miles per hour at an altitude of 10,000 to 20,000 miles above the surface, circling the Earth about once per hour.  The electrons orbit the Earth eastward at about 2,500 miles per hour, taking about 10 hours for each lap. Together, these extra particles can dramatically increase the electrical current, known as the ring current, that always flows westward around the Earth.  Maxwell’s equations of electromagnetism tell us that flowing electrical currents generate magnetic fields, and the magnetic field created by this boost in current around the Earth opposes the Earth’s internally generated magnetic field.

The upshot of all of this complex activity, which remains a topic of active study by space scientists, is that the magnetic field at the surface of the Earth can be reduced by a few percent during a particularly severe magnetic storm. Now, one may think that a drop in the Earth’s magnetic field of a few percent, which would barely deflect a compass needle, can hardly make much of a difference.  But the size of the relative change in the magnetic field doesn’t really matter, instead it is what happens within our electrical power grid when  the magnetic field changes at all.

One of the fundamental equations of electromagnetism, Faraday’s Law, tells us that when the magnetic field passing through a loop of wire changes, it induces a voltage in that loop of wire.  This is, in fact, the fundamental principle used to generate electricity at power plants, but during a magnetic storm Faraday’s Law can cause havoc.  The loops of wire that are affected by geomagnetic storms are the high-tension wires of our electrical power grid that are used to carry electricity from one location to another.  At the scale of the Earth, our power grid looks like a bunch of closed loops of wire of different shapes and sizes laying flat on the Earth’s surface.  The potentially disastrous effect of Faraday’s Law on our power grid is due to the size of these closed loops of wire: closed loops made up of power lines can cover areas that are tens to hundreds of miles across, and a large amount of the magnetic field can pass through that large area.  Even a small change in the strength of Earth’s magnetic field, when summed up over the immense size of these loops in our power grid, can lead to a massive voltage spike of thousands of volts in the system.  It’s similar to a light drizzle of rain falling on  a very large concrete parking lot—although the amount of rain in one area is not much, the water falling over the entire parking lot adds up to a lot.

When a voltage is applied to a wire, it drives a current through that wire.  The changes is the Earth’s magnetic field due to a magnetic storm generate huge voltages that drive geomagnetically induced currents in our power grid.  These currents can overwhelm critical components, such as the massive transformers—each nearly the size of a small house—that are critical elements needed to transfer electricity efficiently over long distances.  In March 1989, an intense magnetic storm sparked geomagnetically induced currents that blew up one of these massive transformers in Quebec, Canada, leaving three million people without electricity for nine hours.

PowerGrid_Quebec.jpgTransformer Damage from Magnetic Storm:  (Left) Image of electrical lighting visible from space at night on the eastern seaboard of North America. (Upper right) Typical size of an electrical power transformer. (Lower right) Damage to one of these transformers in Quebec, Canada due to a severe magnetic storm on March 13, 1989. 

But the destruction of a single massive transformer and the loss of electricity for a good chunk of a day is just a small taste of how wrong things can go during a magnetic storm.  Much larger magnetic tsunamis have occurred in the past, with the most recent being the Carrington Event in 1859, and estimates are that today a similar magnetic tsunami from the Sun and the consequent magnetic storm at Earth could cause an estimated trillion dollars worth of damage.  If not just one, but a dozen or more, of the transformers were destroyed, it could take months to restore electrical service to some areas.  The reason is that, at any one time, only a few spare  transformers exist.  If a major magnetic storm were to destroy dozens of these vital components of our power grid at once, it could take months to build the necessary replacements for recovery.

How would your life change if one morning you woke up to discover that the power was out, and would not be restored for at least three months.  If you have teenagers, particular, it could be quite bad.  Since everything is dramatic to a teenager, how catastrophic would be the loss of electrical power to charge their cell phones and run their laptops and video games systems?

Oh, but wait, the fun doesn’t end there.  All of those ions and electrons dumped by the magnetic tsunami into the Earth’s magnetosphere don’t just circle the Earth harmlessly until they are eventually scattered and lost.  They also increase the density of high-energy protons and electrons in the Earth’s Van Allen Radiation Belts, able to directly damage satellites that operate in orbit around the Earth.

On January 13, 1994, a major magnetic storm dumped a huge amount of plasma into the Van Allen Radiation Belts.  The cumulative effect of the additional high-energy protons and electrons in the radiation belt affected the guidance systems of the Intelsat K, Anik E-1, and Anik E-2 communications satellites.  Although Intelsat K began to wobble and lost antenna coverage, a backup system enabled normal operation to be recovered by the end of the day.  But the intensity of the high-energy protons and electrons caused the guidance systems on both Anik E-1 and E-2  to fail, and both began to spin out of control.  Although the backup guidance system of E-1 was able to stabilize the spacecraft within 8 hours, the backup system failed on E-2, and it appeared the satellite might be a total loss.  But clever engineers were able to use ground control for the satellite thrusters to eventually bring the satellite under control, but it took five months and cost $50 million dollars for the heroic efforts to save the satellite, finally restoring the spacecraft to service in August 1994.

Finally, the boosted plasma density at satellite orbits during geomagnetic storms increases the drag on satellites, requiring the use additional fuel to keep the spacecraft in its nominal orbit.  Over time, the extra use of fuel will shorten the overall lifetime of satellites, because they will run out of the fuel needed to correct their orbits.

So Is There Any Good News?

Solar flares, proton hailstorms, and magnetic storms may sound like a lot of inconvenience to you, interrupting your favorite satellite TV transmissions or preventing you from charging your cell phone, but it’s not all bad.  Just like the fun of watching lightning dancing in the sky from your bedroom window during a thunderstorm, space weather leads to one of the best shows on Earth: the aurora.  Although it occurs at such a high latitude that few people ever get the chance to see the northern lights for themselves, there’s plenty of opportunity nowadays to view this natural light show on the internet, even some mind-blowing views from the international space station flying over the aurora, as seen below.  Next time, join me as we delve into the domino effect of space weather occurrences that leads to the light show of the aurora.

24204469670_22435fdeab_o.jpgThe Aurora Borealis seen from the International Space Station:  NASA astronaut Scott Kelly and ESA astronaut Tim Peake shot this beautiful image of the aurora over the Pacific Northwest from the International Space Station on January 20, 2016. Credit: ESA/NASA.

Getting Familiar with Space Weather: What Happens at the Earth During a Day of Calm Weather in Space?

An angry sun at the center of our solar system from time to time blasts the planets with solar flares, proton hailstorms, and magnetic tsunamis. These aspects of space weather are the phenomena that come from the sun. The remainder of the often confusing assortment of space weather terminology describes how the Earth is impacted by the light waves, particles, and magnetized plasma that the sun occasionally launches in our direction, delineating myriad different consequences for our lives and technology.

Of course, we not only want to know what weather is, but also how it may affect our lives. Knowing that rain is made up of water droplets falling from the sky is important, of course, but we really want to know if an unusually potent rainstorm will lead to swollen rivers, broken levies, and flooded homes. Likewise, when a billion of tons of magnetized plasma is hurtling towards us from the sun, a magnetic tsunami, we really want to know if this space weather phenomenon will trigger a major magnetic storm, potentially inducing massive over-voltages in the power grid and thereby causing a widespread blackout. Here we will explain how the primary space weather phenomena—solar flares, proton hailstorms, and magnetic tsunamis—impact the Earth and potentially disrupt our lives.

Fortunately, the Earth’s magnetic field and atmosphere protect humans and other biological life on Earth from being directly impacted by the harmful effects of solar flares, proton hailstorms, and magnetic tsunamis. Nonetheless, these carriers of the sun’s mass and energy to the Earth can adversely affect the space environment around the Earth, potentially playing havoc with the advanced technologies upon which we depend daily, including electrical power, intercontinental air travel, satellite communications, and GPS navigation. On Earth, of course, our terrestrial weather changes from day to day, hour to hour; one day may be pleasant with plenty of sunshine and a light breeze, while the next day is racked by the dark, threatening skies that foretell a coming thunderstorm. Space weather varies from one day to the next as well, so let’s see what makes a day of fine weather in space, and what happens when a stormy sun shatters that calm.

The Warmth of Sunlight upon your Skin

On many days, the surface of the sun is relatively quiet, with no sign of the sporadic bouts of violent activity that can launch extreme space weather towards the Earth. On such a fine day in space, the sun bathes the solar system with the steady, warm glow of its light. Physics dictates that any object emits a spectrum of electromagnetic radiation that is determined by the object’s temperature. Electromagnetic radiation is a general term that includes a wide assortment of different waves, from radio waves to microwaves, from infrared light to visible light to ultraviolet light, and from x-rays to gamma rays (here listed in order of decreasing wavelength, or increasing energy). On a quiet day, the sun’s spectrum of light is not much different than a giant light bulb in space glowing at around 6000 degrees Celsius. Most of the sun’s radiation emerges as visible light, containing every color of the rainbow. A smaller fraction of the sun’s energy emerges as infrared light (like the warmth we feel from a campfire) and ultraviolet light (why we need sunblock on a sunny day). A vanishingly small amount of the sun’s energy arrives in the form of x-rays, which are quite thoroughly absorbed high in the Earth’s atmosphere before reaching the surface.


The spectrum of electromagnetic radiation

The ultraviolet light from the sun is also largely absorbed by ozone and other gases in the atmosphere, often with enough energy to kick out an electron from a neutral gas atom or molecule, leading to significant ionization of the upper atmosphere during the day. All of the ions and free electrons created by this process form the Earth’s ionosphere, which shrinks, but does not entirely disappear, at night time. This layer of ionized gas is essential for long distance high-frequency (HF) radio communication, helping ham radio enthusiasts to beat the curvature of the Earth by bouncing radio waves off of the ionosphere, enabling communication with distant locations beyond the local horizon.

Although the surface of the sun, called the photosphere by scientists, is a toasty 6000 degrees Celsius, further up in the atmosphere of the sun, known as the solar corona, the temperature rises rapidly to reach scorching temperatures of over a million degrees Celsius. How the solar corona is heated to such phenomenally high temperatures remains a mystery to scientists, one of the longest standing questions in our exploration of the sun and the solar system. In fact, the heating of the solar corona is such a fundamental question that NASA has long pursued plans to send a spacecraft mission to the sun to measure it directly. These plans are finally coming to fruition with Solar Probe Plus, a billion-dollar spacecraft mission to sample the outer reaches of the solar corona, due to launch in 2018.

From the Mind of a Scientist Comes the Solar Wind

Although hazardous storms on Earth—thunderstorms, hurricanes, blizzards, and tornados—may seem massive to a family cowering in the relative safety their home’s basement, on the scale of the planet Earth these ferocious events are confined within the very thin layer of the Earth’s atmosphere. Above the center of the Earth sits about 4000 miles of iron, molten lava, and solid rock. Resting upon the Earth’s surface, the atmosphere extends just about another 60 miles further, just 1.5% of the radius of the Earth. From space, the atmosphere looks like little more than a thin shell of blue haze. All of the fury of a hurricane extending over a thousand miles across the ocean is encased within the lowest layer of that 60~km thick shell.

(Left) The thin blue haze of the atmosphere above the Earth’s surface seen from the International Space Station. (Right) The thousand mile span of Hurricane Katrina over the Gulf of Mexico.

Soviet Luna 1 spacecraft, launched January 2, 1959.

A fascinating fact is that the solar corona (the atmosphere of the sun) is different from the atmosphere of the Earth in a fundamental way. The nitrogen, oxygen, and other gases that make up the air in our atmosphere are held in a state of rest by Earth’s gravity. Although winds andstorms may push those gases across the surface, they remain in a relatively stable set of horizontal layers. In 1958, a young physicist at the University of Chicago, Professor Eugene Parker, used mathematical equations to deduce that the ionized gases (or plasmas) that constitute the solar corona cannot be in a similar state of rest. Instead, the million-degree solar corona must be constantly blowing away from the sun, flowing out into space, ultimately reaching supersonic speeds. This theoretical prediction of a “solar wind” was greeted by the world’s foremost astrophysicists with derision, but the Soviet Luna 1 spacecraft, launched one year to the day after Professor Parker first submitted his findings to the Astrophysical Journal, confirmed the existence of this supersonic flow of plasma emanating from the sun.


Indeed, the solar wind is now known to blow away from the sun in all directions, varying in speed from around 600,000 to 1,800,000 miles per hour. The solar wind is a hot and very tenuous plasma, an ionized gas made of mostly hydrogen and helium, basically a collection of protons, electrons, and alpha particles (alpha particles are nuclei of helium atoms stripped of their electrons, each containing two protons and two neutrons). The temperature of the solar wind plasma is about 100,000 degrees Celsius, but its density is extremely low, with only about 10 protons in one cubic centimeter, about the volume of one of a typical pair of playing dice (not the big fuzzy kind found on car rear view mirrors in the 1970s, but the kind used to play a game of Monopoly). Compare this to the density of the air we breath, which has about 10 billion billion molecules of air in that same size playing die. This solar wind blows steadily through the solar system on a calm day in space, reaching out beyond the planets to the outer edge of what is known as the heliosphere, the realm of influence of our sun in the Milky Way Galaxy.


Illustration of the solar wind blowing from the sun, impacting the protective magnetic field of the Earth.

Magnetic Fields and the Aurora

But the protons, electrons, and alpha particles that make up the solar wind do not flow alone. The solar wind plasma drags along with it the magnetic fields that emerge from the sun. This magnetic field does not always just come along quietly for a ride with the solar wind, but rather it can stir up a bit of space weather action even under calm conditions.

As it turns out, a magnetic field cannot typically generate a plasma, and likewise a plasma cannot pass through a magnetic field. This peculiar fact is why the solar wind must drag the embedded magnetic field along with it, and also why the Earth’s magnetic field can serve as a protective shield against the million-mile-per-hour gales of the solar wind. But when one plasma with its embedded magnetic field impacts another plasma and its magnetic field, the relative direction of the two magnetic fields influences the outcome. The magnetic field of the Earth is oriented so that the magnetic field above the surface points toward the north pole, providing the basis for centuries of navigation by humankind. If the remnant of the sun’s magnetic field embedded in the solar wind is also pointed toward the north, then the solar wind plasma will simply spread out and pass around the Earth’s protective magnetic field. But if the magnetic field embedded in the solar wind happens to the pointed instead toward the south, those two separate magnetic fields can merge together in a process called magnetic reconnection, enabling the plasma from the solar wind to penetrate into the Earth’s protective magnetosphere.

This process of magnetic reconnection sweeps magnetic field lines from the side of the Earth facing the sun (where it is day time) all the way to the other side of the Earth away from the sun (where it is night time), piling up the magnetic field on the night side. Eventually, enough of the magnetic field can pile up on the night side of the Earth to cause the magnetic fields there to undergo further sporadic bouts of reconnection more than 40,000 miles above the Earth’s surface. This subsequent reconnection of the magnetic fields releases the built-up field at the night side back into the flowing solar wind. When this occurs, the magnetic field lines connected to the Earth undergo an abrupt shift. This shift travels along along the Earth’s magnetic field down towards the surface as a particular kind of magnetic wave, called an Alfven wave, just like the bump that travels along a garden hose if you quickly yank it up and down. When these Alfven waves reach an altitude of about 6,000 miles above the surface, they can accelerate a small number of electrons to incredible speeds of nearly 40 million miles per hour. These electrons speed down the magnetic field lines towards the Earth, and when they reach about 100 miles in altitude, they begin to collide with the molecules in the much denser atmosphere below. The collisions excite the air molecules, causing them to radiate away the energy of the collisions as the dancing lights of the aurora.


Illustration of magnetic reconnection occurring on the night side of the Earth, triggering the glowing of the aurora.

If magnetic field in the solar wind remains pointing southward, this process of sweeping the magnetic field from the day side to the night side of the Earth will repeat itself every three hours or so, with repeated occurrences of the aurora dancing in the skies of the polar night. Scientists call this process a substorm. It is somewhat analogous to a period of scattered thunderstorms on a summer afternoon in the American Midwest. On a sunny afternoon, the wind picks up as the skies to the west darken. Before long, the winds howl, heavy rain pelts the ground, lightning flashes, and thunder rolls across the plains. Not long afterwards, the storm eases to a cold light rain, the thunder and lightning fade into the distance, and the clouds eventually cede to the emergence of the hot summer sun, evaporating the recent rain, returning to a hot, and often sticky, summer afternoon. And, if another scattered storm is headed your way, the process will repeat itself. Substorms are the space weather equivalent, breaking up a fine, calm day in space with a predictably choreographed magnetic dance far above our atmosphere, a fraction of its energy channeled into a dazzling auroral display.

The Van Allen Radiation Belts

A final important characteristic of near-Earth space that persists, even on quiet space weather days, is the system of Van Allen Radiation Belts. The Earth’s radiation belts were first discovered in 1958 by Professor James Van Allen of the University of Iowa with the Explorer 1 spacecraft, the first United States mission to orbit the Earth (the third man-made object to orbit the Earth, after the launches of Sputnik 1 and 2 by the Soviet Union, which sparked the Space Race during the Cold War). Not significantly different from the magnetic field due to a bar magnet (which you may have seen with the trick of using iron filings to reveal the magnetic field lines), the Earth’s magnetic field emerges from Earth’s surface near the south pole, directed northward along longitudinal lines (like the thick black lines on basketball, or the boundaries between the slices of an orange), spreading out over the space surrounding the Earth, only to converge again as it passes back down through the surface near the north pole. Scientists call this basic shape of the Earth’s magnetic field lines a dipole geometry, somewhat similar to the shape of a cored apple.

(Left) The magnetic field of a bar magnet revealed by iron filings. (Right) The dipole magnetic field of the Earth.

As it turns out, high-energy protons and electrons can be trapped in this dipole-shaped magnetic field, collecting largely in a ring around the Earth’s equator, at an altitude of ten to twenty thousand miles above the surface, forming  the Earth’s Van Allen Radiation Belts.  In addition, these trapped protons (and other positively charged ions, like oxygen) drift in a westward direction around the Earth at a speed of about 25,000 miles per hour, encircling the Earth in roughly an hour; the negatively charged electrons drift to the east, at about 10% of the ions’ speed, encircling the Earth about twice a day. Together the drift of these ions and electrons forms the ring current that encircles the Earth. Because Maxwell’s equations of electromagnetism tell us that a flowing current will generate a magnetic field, this ring current modifies the Earth’s magnetic field. On quiet days, this ring current is relatively steady, not leading to any significant changes of the Earth’s magnetic field. But, as we will see, during periods of stormy space weather, abrupt changes in the ring current can disturb the Earth’s magnetic field, leading to significant changes of the magnetic field, even down at the Earth’s surface, potentially disrupting the electrical power grid and causing widespread blackouts.


Schematic of the Earth’s Van Allen Radiation Belts.

And Then the Weather Turns . . .

Now that we know what constitutes a pleasant day of weather in space, join us next time as we learn how the Earth is affected when space weather turns ugly.

Getting Familiar with Space Weather: What Comes from the Sun?

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.