Solar, Space, and Geomagnetic Weather, Part II
By Stephanie Osborn
“Interstellar Woman of Mystery”
Rocket Scientist and Novelist
Last time, we talked about the corona, the solar wind, the solar magnetic field, coronal holes, and solar cycles. But wait! There’s more!
At Solar Max, there’s a lot of activity. Lots of sunspots, lots of flares and other kinds of eruptions. 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. Yeah, you heard right — this is one of the few times when the old trope about “reversing the polarity” is actually the correct answer. The end that was North becomes South, and the end that was South becomes North. MORE, the ENTIRE solar magnetic field ALSO flips! (This got very complex this last time; it wasn’t as fast and simple. It took nearly six months, and for a time our Sun had something like FOUR South poles, and NO North poles. Yeah, stellar magnetics gets crazy.) 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.
As the solar cycle winds down from Max to Min, the process starts all over. New magnetic snarls form deep in the Sun near the new poles, and gradually move to the surface and drift toward the equator. But while this is occurring, the photosphere tends to get quiet.
As the sunspots start to reach the photosphere again, the Sun starts ramping back up from Solar Minimum to Solar Maximum, and another active period accompanying a pole flip. Over and over and over, every eleven years on average.
In addition there are longer cycles that we are still working on figuring out, because they’re tens to hundreds of years long, and it’s hard to get data that goes far enough back to chart those. However, a recent development called the double-dynamo model (we’ll talk more about it later) is helping to explain 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 bacon, 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. If you really want to observe the Sun, the best way is to get a telescope, aim it at the Sun, and hold a sheet of white cardboard behind the eyepiece. Adjust the distance until you get an image of the Sun projected on the cardboard. This is a cool way to watch solar eclipses, too. If you don’t have a telescope, grab a shoebox, punch a small hole in one end, turn it upside down and point the hole at the Sun, then tilt the thing around until you get a small image inside the opposite end of the box.) Sunspots aren’t really dark at all; they just APPEAR dark because of the contrast with the surrounding hotter, brighter photosphere.
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. The bright blue-white spot in this next solar image is a flare.
Up close, it can look something like the next image. (Also let me take this opportunity to point out that the images I’m using are taken in various spectral regions, but almost none of them are taken in visible light, and all of them use “false-color” schemes to enhance detail. Remember what I said about finding the right ways to see the details of what’s happening? Different spectral regions — certain parts of the visible, infrared, ultraviolet, x-ray, and more — are ways to do that, because the particular frequency emitted is determined by the element — or the energy/temperature — of the particle emitting the photon.)
And then there are the CMEs. Coronal Mass Ejections. In the image above, the white light is the flare, and the orange and red “flame” coming off it is a prominence becoming a CME. Below is a video of a “filament” aka prominence lifting off to become a CME.
I’m never quite sure how to best anthropomorphize 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 involves something called magnetic reattachment — where those mag field lines break and then reattach to another one closer by.) And it is like a giant nuclear bomb, blowing a big bubble of plasma away from the Sun at high speeds. If the flare is the bomb’s explosion, the CME is the mushroom cloud.
See the big blue blob above the Sun in this image? That’s a CME screaming off the Sun.
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.
Comet Tales blog/Osborn Cosmic Weather Report: http://stephanie-osborn.blogspot.com/