Monday, May 7, 2012

Solar, Space, and Geomagnetic Weather, Part 2

But wait! There's more!

At Solar Max, the coronal holes move away from the Sun's poles and group in with the sunspots, spewing high-speed solar particles out into the plane of the solar system.

At the end of every 11-year cycle, the magnetic orientation of the spots...flips. The end that was North becomes South, and the end that was South becomes North. It takes a whole 'nother cycle to get back to the way it started out. So that's a second solar cycle, the 22-year cycle.

In addition there are longer cycles that we are still working on figuring out, because they're hundreds of years long, and it's hard to get data that goes far enough back to chart those.

Now, sunspots look dark not because they're cold, but because they're just a bit cooler than the surrounding plasma of the photosphere (which is the visible “surface” of the Sun). If the photosphere is about 5,800°K (~10,500°F), then the sunspots are about 3,000-4,500°K (4,900-7,600°F). Still plenty hot enough to fry your turkey, but still several thousand degrees cooler than their surroundings. They can be teeny-tiny (relatively speaking, of course) or they can be huge things (80,000km/50,000mi – not too shabby when you consider the Earth is about 13,000km/8,000mi diameter) big enough to be seen by the naked eye (but don't do that – we like having eyesight.)

So you might reasonably expect that during a solar max the Sun would be cooler, and send less energy out into space, right? Well, at first glance you might think so, but that isn't really how it works. Remember, a sunspot is a big magnetic snarl. And the plasma around it follows the lines in that snarl. So we get all those great big loops – prominences and flares and things like that. Occasionally, like a snarl in your hair, the lines break – but unlike your hair, they reattach, producing really spectacular flares.

And then there are the CMEs. Coronal Mass Ejections.

I'm never quite sure how to best anthropomorphise a CME. Are they solar belches, or sneezes? Suffice it to say that all of that magnetic field mess around the sunspot group causes some sort of explosion. (No, we don't know exactly why. We do know it's really, really complicated.) And it is like a giant nuclear bomb, blowing a big bubble of plasma away from the Sun at high speeds.

So between the coronal holes increasing both the speed and density of the solar wind, and these CMEs exploding into the solar system, the most active time for the Sun is in fact solar max, and that is when it's pumping more energy into the solar system, not less.

I know, I know - that doesn't make sense. Let's talk about the details next week.

Stephanie Osborn

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