What is Space Weather?

Space Weather is a term used to describe the relationship between the sun, the Earth, and the technological systems upon which we rely.  It is a complicated chain of physical processes (predominantly electromagnetic) that links the solar atmosphere, the Earth’s magnetic field, the Earth’s atmosphere, and the Earth’s crust.  Satellites, airlines, GPS signals, and the power grid are all vulnerable to the effects of space weather.

It Starts at the Sun

The Sun’s surface and atmosphere are incredibly dynamic.  These regions consist of plasma, which is an electrically charged gas.  The Sun has a strong and complex magnetic field.  Plasma organizes about magnetic field lines, creating the solar filaments and coronal loops, shown early in the above video.  This organization is caused by a fundamental property of plasma called the frozen-in theorem: the charged particles inside of plasma can move along magnetic field lines, but not across them.  In the Sun’s atmosphere, the pressure of the hot plasma gas is constantly fighting the forces of the Sun’s magnetic field, creating a tenuous environment that is eager to release this tension.

Solar plasma is hot, so it blows off into space to create the solar wind.  The solar wind fills our solar system with hydrogen, helium, and other trace elements.  It pulls the Sun’s magnetic field into space with it, where it is known as the Interplanetary Magnetic Field or IMF for short.  The solar wind moves through space at a brisk 400 km/s (just under a million miles per hour).  It takes around 4 days for the “quiet” solar wind to reach Earth.  The solar wind is highly variable, however, and can reach much faster speeds.

When certain regions on the Sun’s surface become unstable, explosive releases of energy occur.  These include solar flares, which are bright explosions of light and particle radiation (think of small particles moving almost the speed of light!)  These are sometimes associated with Coronal Mass Ejections, or CMEs.  CMEs are when a portion of the Sun’s atmosphere explodes into space all at once.  The amount of gas in a single CME can surpass the amount of mass within a single Earth mountain if it was vaporized.  These events create bursts of strong solar wind: it is denser (more plasma), faster (thousands of kilometers per second), and carries a stronger IMF.

The Earth as an Obstacle in the Solar Wind

The Earth has a strong dipole magnetic field that has the following geometry:

Source: NASA.gov illustration from http://www.nasa.gov/sites/default/files/images/607968main_geomagnetic-field-orig_full.jpg
Source: NASA.gov illustration from http://www.nasa.gov/sites/default/files/images/607968main_geomagnetic-field-orig_full.jpg

Because of the frozen-flux theorem, described above, the solar wind plasma cannot pass through the Earth’s magnetic field lines.  Instead, just like a large rock in a shallow stream, the solar wind flow is re-routed around the Earth’s field.  This creates the magnetosphere, or a cavity in the solar wind flow.  The energy transfer from However, unlike the simple rock-in-a-stream analogy, the relationship between the solar wind and the Earth’s magnetosphere is an electromagnetic one.  The magnetic obstacle to the solar flow isn’t solid; it compresses on the dayside and stretches into a long magnetotail on the nightside.  The energy of the flowing solar wind is transferred to the magnetosphere by forming electric currents and electric fields around and through the magnetosphere.  Plasma within the Earth’s magnetosphere is accelerated, intensifying the radiation belts.  Electric currents and particles flow along magnetic field lines and into the Earth’s upper atmosphere, driving the beautiful aurora.  The Earth’s magnetic field is perturbed, twisted, and warped compared to its more regular dipole shape.  The entire process is dynamic and complicated.

While the speed and density of the solar wind are both important in controlling the energy transfer to the magnetosphere, the most important factor is the direction and strength of the interplanetary magnetic field (IMF).  When the IMF is southward (that is, it is directed from north to south with respect to the Earth’s magnetic poles), it is oppositely aligned with the Earth’s magnetic field, which points northward at the dayside of the magnetosphere.  Oppositely aligned magnetic fields can go through a process known as reconnection.  This is where the IMF lines merge with those lines that are connected to the Earth.  Because the new lines are flowing along with the solar wind, they are peeled off the day side of the magnetosphere and dragged to the night side.  These eventually recirculate to the dayside in a process known as magnetic convection.  The movie above shows magnetic convection in action.  Magnetic convection is important because it is the main way through which plasma is energized to dangerous levels.  It also allows electric currents to flow into the upper atmosphere.  Therefore, if you want to know if a solar storm will become a space weather storm at Earth, you need to know the direction of the IMF!  Southward IMF is what causes the strongest space weather events.

Our  Vulnerability to Space Weather

An interesting event occurred on September 1st of 1859: Richard Carrington, an amateur solar astronomer, witnessed an incredibly strong solar flare.  18 hours after his observation, world-wide auroras filled the sky and the largest space weather storm ever observed by humans was in full swing.  During this storm, telegraph wires ran without power; some stations sparked and caught fire.  For the first time, we were experiencing the effects of space weather on technological systems.  

A diagram of some of the ways in which space weather affects human-made technological systems.  From the U.K. Meteorological Office.
A diagram of some of the ways in which space weather affects human-made technological systems. From the U.K. Meteorological Office.

Today, we are more vulnerable to space weather than ever before.  Here are some of the most critical space weather effects:

  • Spacecraft are naked to the particle and X-ray radiation associated with solar flares and solar storms.  This can damage solar arrays, drive electric discharges across electronics, and deteriorate spacecraft materials.  Spacecraft behavioral upsets due to space weather are common.  Several spacecraft have famously been rendered temporarily inoperable and even destroyed by space weather storms.
  • Because much of the energy of space weather storms flows into the high-latitude regions of the upper atmosphere, it becomes very disturbed during space weather storms.  This causes scattering and distortion, or scintillation, of signals between spacecraft and the ground.  This is especially important for GPS signals, which cannot accurately report positions during active space weather times.  Next time your GPS navigation system is failing, check the space weather conditions.
  • Along with electric currents, particle radiation flows along field lines and into the the upper atmosphere.  While the atmosphere shields us from harm while we are on the ground, the passengers and crew of polar-flying aircraft are at increased radiation risk during space weather storms.
  • The electric currents flowing through the upper atmosphere can induce currents in any long, ground based conductor.  While this usually means conducting minerals in the Earth’s crust, the currents can also flow through long pipelines and power lines.  This can heat and corrode pipes, heat power transformers, and disrupt the power grid.  In March of 1989, a strong space weather storm caused the collapse of the eastern Canadian power grid for 9 hours.  There are many documented cases of large, high voltage transformers being completely destroyed during space weather events.

If a space weather storm on the level of the famous 1859 “Carrington Event” were to happen today, the impact would be catastrophic.  Experts predict that nation-wide power outages would last at least a month as companies struggle to replace transformers and other damaged infrastructure.  Communication capabilities would be severely crippled, possible long term with the loss of multiple satellites.  The impact on the economy is estimated to be in the trillions of dollars.