*My apologies to Stephanie AND the readers on putting this up so late. I meant to cue it yesterday, but it was one of those nights one minute I was at the computer and the other I was in bed and asleep, with no memory of anything in between. Probably because I’d been up since four am.- SAH*
Solar, Space, and Geomagnetic Weather, Part III
By Stephanie Osborn
“Interstellar Woman of Mystery”
Rocket Scientist and Novelist
So we’ve talked about coronal holes, the solar wind, solar cycles, sunspots, flares, and Coronal Mass Ejections (CMEs). Now, mind, of all of those, there are really only two that can reach us. One is the solar wind, and any enhanced wind streams from those coronal holes. And the other is a CME.
(That said, the X-rays from a solar flare can and do reach us and cause their own problems. We’ll touch more on that when we cover NOAA’s solar/geomagnetic weather indices.)
Just what effects do coronal hole wind streams and CMEs have on Earth?
Now, we’ve talked several times about a bar magnet, with its field lines traced out by iron filings on a piece of paper. And we all know that that is a nice, symmetric image.
But the Earth’s magnetic field (aka magnetosphere aka geomagnetic field) is not nice and symmetric. This is because the solar wind is pushing on it. So the side toward the Sun has a “bow shock” and is compressed, and the side away from the Sun is stretched out into a tail. Like this:
Here’s a little more close-up detail:
Note the Van Allen radiation belt in this image. All those charged particles can get caught up into our mag field and cause higher levels of radiation. They ping back and forth between our North and South poles and eventually enter the upper layers of the atmosphere. We’ll talk more about that in a minute. The more charged particles hit our magnetosphere, the more get caught in the Van Allen Belts (VAB), and the more apt we are to have atmospheric effects. So an enhanced solar wind stream (EWS) from a coronal hole can generate some interesting phenomena.
But the granddaddy of those phenomena is caused by a coronal mass ejection hitting Earth. Because those suckers are (relatively) dense and VERY energized. And it might look something like this:
[NOT TO SCALE.]
[No. It’s not. Really.]
Worse…remember how flares are the detonations caused by “magnetic reattachment”? Well, if a CME is powerful enough, it can put so much stress on the magnetotail (that part stretched off to the right in these images) that it can snap off, and reattach closer to Earth! The energy feedback from THAT can get pretty powerful, too!
How energetic IS all this stuff?
Well, these events can actually raise the temperature of the outer layers of the Earth’s atmosphere (the thermosphere, aptly named) sufficient to cause it to expand. This affects us, because that increases drag on satellites and spacecraft, and can cause the orbits of satellites to decay and re-enter well before they were intended. This is really bad if it’s something important, like a weather satellite during hurricane season. After all, if the people of Galveston had had weather satellites in 1900, the city could have been evacuated well before it got hit, because they would have known it was coming for days. If we DON’T have weather satellites because we’ve lost ‘em to increased atmospheric drag, we might as well go back to those days, as far as weather prediction is concerned. Ditto communications satellites. Don’t even mention GPS.
It affects manned spacecraft, too. Shuttle and Station did and do, respectively, have problems maintaining orbital altitude when all this causes the atmosphere to swell. Stationkeeping maneuvers/burns must occur more often. A spacecraft in Low Earth Orbit (LEO) that is not being maintained with active stationkeeping IS going to come down sooner or later. Probably sooner.
Disruption of the Earth’s magnetic field can be a problem. It can disrupt radio communication (including cell phones) rather severely. It can damage satellites that remain in orbit. It can generate “induced current” in any lengthy conductor. Let’s pause for a moment and talk about that.
Induced current is a way of using magnetic fields to generate electricity. Remember how I said, back in part I, that the “current” of plasma created by the Sun’s rotation on its axis generated a magnetic field? The reverse is also true. A moving magnetic field can generate an electrical current in any conductor placed within the field. So the disruption of the geomagnetic field constitutes a “moving” magnetic field and will induce electrical currents in everything from power lines to pipes and conduits.
When these truly huge induced currents hit things like transformers and circuit breakers and power stations, they can quickly overload them. This, in turn, can (and has) cause(d) blackouts and brownouts, particularly in parts of the country/world where the power grid is not robust enough to handle significant surges. (Given that most large substation transformers are still hand-built, and have a lead time of months between determining need and installation, that could be a real problem.)
Long pipelines, like the Alaskan Pipeline, can be affected as well. In fact corrosion is occurring at a higher rate than expected because its northerly location exposes it to such induced currents all the time (remember that the ends of a bar magnet’s field are open). And there are plenty of those.
Here’s a map created by Samuel Bailey (firstname.lastname@example.org) of gas pipelines just in the EU and Russia, for Wikipedia. And all of these will develop induced currents.
Here’s another map of the natural gas pipelines just in the continental USA.
Around the world, long-span pipelines carry water, oil, natural gas, ammonia, alcohol fuels, and in places, hydrogen. Some of these could cause problems with induced currents.
And this same moving magnetic field that induces currents in conductive manmade structures also causes the aurorae.
Most of you reading this have heard of the Northern Lights, properly termed the Aurora Borealis, and many may have seen them; but there are also the Southern Lights, the Aurora Australis. The Aurora Australis is much harder to see, because there is considerably less land mass in the Southern Hemisphere in a position TO see them — only Antarctica, extreme southern Australia, the extreme southern tip of South America, and perhaps New Zealand. These are actually ovals that circle the magnetic poles of Earth (and most other planets with magnetic fields, by the way. They’ve been photographed on Jupiter). Here’s an image of a particularly strong auroral oval that occurred around the South Pole in 1989.
They happen where the charged particles that have been caught up from the solar wind or CME into the geomagnetic field follow the field lines down into the atmosphere. The gas molecules become excited into a higher energy state, then discharge that extra energy as light. This is very similar — in fact, essentially the same — as a fluorescent light bulb, only natural and not contained. The colors are determined mostly by the main gas that is fluorescing. Carbon dioxide produces white light; nitrogen, pink or red; oxygen, green or blue. (It can also generate ozone.)
Now, having talked about all of this radiation that an increased solar wind and coronal mass ejections pump into our Earth’s system in general, and the fact that there are more of these things when there are more sunspots, when do you think the Sun is sending out more energy, Solar Max, or Solar Min? Yup, despite the logic of sunspots being cooler, the Sun actually sends out more energy during Solar Max, when there are the most sunspots.
Comet Tales blog/Osborn Cosmic Weather Report: http://stephanie-osborn.blogspot.com/