CME, Wind, Flares, Flux and Geomagnetic Storms .. say what?

Foundations of Amateur Radio

When the Sun burps, something that it does regularly, the mainstream media starts talking about aurorae and optionally the end of the civilised world, not always as clinically as that. What's not talked about, let alone explained, is the nature of the solar burp. You've likely heard the terms Coronal Mass Ejection, or CME, Solar Flare and perhaps Solar Wind, Solar and Geomagnetic Storm, and Solar Flux, but what do these terms actually mean and how do they relate?

Let's start with some basic numbers. Our Sun is 150 million kilometres away from Earth. As seen from Earth, the Sun rotates on its axis every 27 days, called a synodic rotation period, because while the Sun is rotating, Earth is moving too. If that wasn't enough, the Sun isn't solid, depending on where you're looking at it, rotation happens at different speeds, faster at the equator, slower at the poles.

You might have heard of the Solar Cycle, an 11 year period during which solar activity steadily increases, near the maximum activity its magnetic poles flip from North to South and activity slowly decreases until the cycle starts again. Until quite recently we've deduced this by counting the number of dark areas, called sunspots, on the surface of the Sun.

All this to say that our Sun is one massively dynamic environment and with it come a whole lot of processes that science is still discovering. The YouTube channel Astrum has a fascinating video called "We Didn't Predict the Sun Would Do This", that describes much of what we're still learning.

We experience the Sun as a source of light, but as a radio amateur you know that light only represents a small set of frequencies in the radio spectrum, it's better to think of the Sun as a radio source, emitting many frequencies at once. The strength of this is measured at 2.8 GHz three times a day at 17:00, 20:00 and 23:00 UTC at the Dominion Radio Astrophysical Observatory in Penticton, British Columbia, Canada. This measurement, the Solar Flux gives a good indication of the level of solar activity. Adjusted for the varying distance between Earth and the Sun, a Solar Flux Index, or SFI, below 70 means that solar activity is very low, above 150 is considered very high activity.

In addition to radio waves, the Sun also spits out a continuous wave of particles. Different parts of the Sun emit these at different speeds, varying between 300 and 800 km/s. These particles, the Solar Wind, exist throughout our Solar system. Bec