(Source: SpaceWeather.com)
I think this is one of the best, simple explanations of space weather that I’ve seen lately:
(Source: NPR)
Space weather, as it is called, originates with solar magnetic activity. The sun is a giant spinning ball of charged particles. In addition to its spin, the heat released from the core through nuclear fusion eventually sets the upper layers of the sun into a kind of boiling motion called convection. All that motion — spin and convection — means lots of charged particles streaming this way and that. Since current (the flow of charges) produces magnetic fields, the outer domains of the sun are ruled by magnetism. Magnetic fields are the source of all those cool images of giant flares erupting in planet-spanning arcades of super-hot plasma. It’s also the source of so-called Coronal Mass Ejections or CMEs, which are, essentially, the space storms that space weather is all about.
CMEs are eruptions of matter and magnetism from the sun into space. A typical CME will blow 10 billion kilograms (about 22 billion pounds) of solar plasma into space along with enough energy to represent a flotilla of 220 aircraft carriers moving at 500 km/s. The fact the CME’s are quite common says a lot about the power locked up in an ordinary star like the sun.
While 1 to 3 CMEs may occur every day, we only the notice the ones that slam into the Earth on their journey across the solar system. When a CME crosses the Earth it runs into our planet’s own magnetic field. Charged particles from the CME get trapped by the Earth’s magnetic field and stream down toward the planet’s surface near the poles.
When those CME particles, running down magnetic field lines, strike atmospheric gas atoms, the collisions cause the atoms to light up like Christmas tree bulbs. That is the origin of the simmering walls of color we called aurora. There was a time when pretty lights were all there was to space weather. Those days are over.