An ill solar wind blows no good

By Phil Plait | September 26, 2008 9:49 am

We take the Sun for granted. It’s there every day (unless you live in the Pacific northwest, of course), shining and warming us. But never forget: it’s a star, a mighty mass of churning ionized gas a million times the volume of the Earth. It’s complex, and surprising.

The latest surprise comes courtesy of the Ulysses spacecraft, currently in its 18th year orbiting and gathering data on our nearest star. One characteristic it keeps its eye on is the solar wind. This stream of subatomic particles blows off the Sun at hundreds of kilometers per second, flinging billions of tons of material into space every hour.

Ulysses measures the Sun’s magnetic field. Click for details.

The solar wind changes over time, reflecting changes in the Sun itself. The magnetic field of the Sun has a 22 year cycle; it goes from minimum strength to maximum every 5.5 years, back to a minimum, then flips polarity (south becomes north and vice-versa), then strengthens again. This is what leads to the 11 year sunspot cycle — the number of spots depends on the strength of the magnetic field, which maxes out twice every 22 year cycle.

Obviously, this is complicated, and not terribly well-understood. Worse, the sunspot/magnetic cycle is different every time, with each period having different strengths, different characteristics. We’ve learned a lot about it, but some details are maddeningly vague.

And that leads to surprises, as I mentioned earlier. We’re at the sunspot and magnetic field minimum right now. That means the solar wind is also at a minimum, but for some reason yet unknown, this particular time the wind is weaker than usual. It’s speed is about the same as usual, but there’s only about 3/4 the usual density of particles in it, so the pressure the wind exerts is lower (think of it this way: a wave of water moving 10 km/hr can knock you over, but a wind at that speed feels gentle. Air is less dense than water, and so at the same velocity exerts less pressure).

What does this mean to us? To be honest, I don’t know. The Sun interacts with the Earth’s magnetic field in a highly complex way. The magnetic field of the Earth protects us from high-speed particles from deep space, for one. The solar wind compresses our field, so a weak wind means the Earth’s field extends higher. That means better protection for our satellites, which is nice.

But like I said, these interactions are complex. Could a weaker wind be somehow bad for us? It’s possible, but I’m not too concerned. We’re at the start of a new cycle; sunspots have been seen which means we’re on our way toward a max again in a few years (2013 or so). However, only a few spots have been seen, and they rapidly faded away. Something weird is going on in our nearest star, that much is certain.

Remember though, people have been around a long, long time, and have no doubt weathered such weirdnesses before. I don’t think our climate is necessarily at risk, or there will be any extinction level events! However, our society depends on electricity, and certainly our power distribution can be affected by solar events. So it’s a very good idea to keep our eyes on the Sun, and an excellent idea to try to understand it better.

[Not to belabor the point (but get used to it), I talk quite a bit about the Sun’s effect on the Earth in Death from the Skies!]


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