Solar, Space, and Geomagnetic Weather, Part IV By Stephanie Osborn

Solar, Space, and Geomagnetic Weather, Part IV

By Stephanie Osborn

“Interstellar Woman of Mystery”

Rocket Scientist and Novelist


“So what the heck are CMEs? I mean, what causes them? In detail this time, please!” you ask. (Or maybe you don’t. But chances are, SOMEONE reading this IS asking it.)


Coronal Mass Ejections are gigantic explosions that occur, usually in the vicinity of particularly active sunspot groups (though not always). We’re still discovering what they are, how they occur, and why they do what they do. It seems to get into some complicated electromagnetic physics and something called “magnetic reconnection.”



Think about it like this. Suppose you have two bar magnets, lying near each other but, say, perpendicular to each other. Each has its own magnetic field, with field lines that go out from one pole and arc around to the other pole (remember our discussion of iron filings a couple weeks ago?), but now we’ve got them close enough that those magnetic fields interact. If you’ve ever played with magnets, you know that, if you hold those two suckers just right, you can make one “float” in mid-air, and even make it spin and gyrate. There’s a lotta expensive, executive-desktop toys based on this. Like this one:

The concept behind the toys is mostly “like repels,” but it gets a little more complex when the toys are MOVING. That means the magnets are moving relative to each other, and the magnetic field interaction gets way more complex to model.

Now suppose — just suppose — a field line broke away from its parent magnet and attached the opposite end to the other magnet? Now suppose a whole SEGMENT of field lines did that. Those bar magnets would start dancing a whirligig, and the magnetic field would go crazy.

Now suppose that the bar magnets are swirling plasma gases, and the field lines are running through more swirling plasma.

THAT is magnetic reconnection. The end result is that a whole bunch of energy gets transferred from the field into kinetic energy. This heats up the plasma AND accelerates it, and, at least on the surface of a star like our Sun, a titanic explosion is the result. A great big blob of plasma goes flying out into space, and that blob is a “coronal mass ejection,” because a big mass of the corona just got ejected from the Sun. (Imaginative name, huh?)

What does magnetic reconnection look like? It looks exactly like this:


So you can think of the reconnection event as being like a titanic nuclear bomb, and the CME is the mushroom cloud moving up…and out, into interplanetary space. (How big a bomb? Well, solar flares vary in size and power. But NASA solar scientists estimate they’re “the equivalent of millions of 100-megaton hydrogen bombs exploding at the same time.” Keep in mind that the biggest nuke ever detonated on Earth was Tsar Bomba, at only 50 megatons.)

The vast majority of them aren’t THAT big, and aren’t even Earth-directed. The chances of one smacking Earth aren’t that great. But because there are a lot of them, especially at Solar Max, it happens fairly often. Sometimes it’s just the edge of the expanding bubble, but sometimes it whacks Earth upside the head. And when they come in, they’re coming fast.




Putting it in motion:

And here’s the beginning of a CME, up close and personal, replayed several times to enhance different features of the event.

Moreover, most of the time as the magnetic field re-forms underneath the developing CME, it can actually accelerate the plasma of the CME out, away from the photosphere and into the solar system.

The WSA-Enlil model is often used to help “track” CMEs as they move through the solar system. It also give you a very good idea of how these things DO move in interplanetary space. Here’s what that would look like.

So what are the general parameters of a CME? Depends on where in the solar cycle you are. If you’re near Solar Minimum, they occur about one every 5 days or so. If you’re around Solar Max, expect one every 6 or 7 hours.

How big are they? If you’re talking volume, that’s gonna depend on how far out from the Sun they are, and how well the interplanetary medium is allowing them to hold together. Note, in the Enlil model, how the thing spreads out as it moves outward.

If you’re talking how massive, well, on average they’re about 3,520,000,000 lb (1,600,000,000,000 kg). That’s over three and a half billion pounds of plasma. On average, their speed is about 304 mi/s or 1.1 million mph (490km/s). IF, however, one follows close on the heels of another, so that the first one has swept most of the interplanetary medium out of the way (decreasing drag), the speed can increase to 2,000 mi/s or 7.2 million mph (3,200 km/s). And with the Sun 93 million miles away, that means a really fast CME can reach Earth in just under 13 hours.

~Stephanie Osborn

Comet Tales blog/Osborn Cosmic Weather Report:


60 responses to “Solar, Space, and Geomagnetic Weather, Part IV By Stephanie Osborn

  1. c4c

  2. BobtheRegisterredFool

    Last thread, I asked if irregularities in CME might also induce the lower voltages Kevin describes as having greater potential for harm. Your essay today seems to confirm that CME are not particularly uniform. What about density, volume, length? What are ranges for the time it might take a CME to pass Earth? I assume the density/cross section, and hence effects are not uniform as it passes around Earth?

    • I don’t want to hijack the thread, so I’ve started commenting on my blog. The lightning arrester post should be up today, and I’m looking at GIC (Geomagnetic Induced Current), now. I’m still not sufficiently up to speed, but ran into several surprising things. One is that, damage wise, we’re basically looking at ginormous ground loops due to difference in potential at grounding points during a solar event. Another was 300 amps measured on the ground in Sweden during a solar storm. A third is different transformers types have different GIC characteristics. The latter might turn out to be more significant and limit damage to one type of transformer, but if so, it’s not why I though a Carrington Event wouldn’t wipe out large number of transformers.

      This is speculation, but one of these things through the ground means that regardless of lightning protection, the current flows through the equipment first. Even with spark gap arresters, this could have been behind some of the damage. But it raises the question of whether the spark gap was close enough in potential to essentially run the GIC through it rather than the equipment during discharge. It’s something I’m having to think about. I’m also going to have to look at my transformer connection books for something.

      Will mention a couple of things. One is that in 1847, Joseph Henry proposed a telegraph spark gap arrester consisting of wire run up the pole to within half an inch of the telegraph wire. This may have been what burned some poles down. The other is that the grid does have equipment that opens with voltage on ground. Got into that twice when we ran distributed generation. Won’t swear to whether this would limit GIC, but it’s something else to think about.

      • Yes, to the telluric currents. This is why grounding in a situation like a Carrington does little good. Really, only a Faraday cage of some substance is going to protect things.

        The spark gap arrester is news to me, but I’m not surprised. And yes, it makes very good sense for why there are reports of poles burning. And it also may be the reason why I can find the reports, but nothing substantive — the use of the things may have still been sporadic at that point, and/or the telegraph companies may not have wanted to admit that their safety feature functioned as a spark plug instead.

        • The telluric currents are what’s giving me conceptional issues right now. At times I thing i almost see it in my head, but then it either goes away, or maybe I’m not visualizing it right.

          The issue is that the bulk of transmission in the US doesn’t have a neutral. It’s three-wire Delta. Once at a distributions station, it’s stepped down to Wye, which does have a neutral. Technically it’s a Delta-Wye (AKA Delta-Star) connection.

          I’m trying to visualize how that difference in potential can be propagated through three-wire Delta. Yes, all three coils on the low side are connected to neutral and grounded, but the high side isn’t. It’s possible for currents on the low side to be passed to the high side, of course, but here we’re dealing with a difference in potential passed along with no physical connection.


          Haven’t had a chance to look at it this weekend, and what transformer books I have didn’t offer any insight. Grasping that would go a long way in examining this problem.

          • Okay: something just isn’t making sense. The sketch of what happened in Sweden is of transformers connected in Delta -Wye, well the sketch was a common short-hand that showed the low (secondary) side coils connected directly to the lines. That’s obviously not the case. Now, if you have a strong current flow on the low-side of a transformer, it will step-up and travel on the transmission line (important note: home generators improperly connected can energize distribution lines – not a good thing). But the current flow has to be through the coils on the secondary side.

            The sketch of the Sweden incident has a ground-loop from the ground at one transformer through the ground of the other. But the primary side coils are not tied to ground. In other words, the paper I saw is essentially claiming that the difference in ground potential is somehow passed through the coils without a connection. Current flow, yes: difference in potential, no.

            I’m going to strongly disagree with grounding having little advantage during a Carrington Event because of what it does. For instance, the possibility of short-circuiting a ground loop by passing current through a lightning arrester at the same ground potential as a transformer.

            I’m having suspicions about circulating currents, but at this point it’s only suspicions. If my suspicions are correct, a Faraday cage wouldn’t accomplish much. My suspicions could be wrong, though.

        • Based on what I’ve seen at work, a detailed explanation isn’t always requested by the public. We’ve gone into detail when it was requested, but that can be rare.

          Pole fires during the Carrington Event may have fallen into the same category. Telegraph linemen probably knew, either from coming across it or from hearing of someone who had. A simple “It caught the pole on fire” probably sufficed, and they’d probably have gone into details if someone at the time was curious enough to ask.

        • Stephanie:

          Do you have any max values on a Carrington Event GIC? I’ve so rusty, just looking at a matrix makes squeaky gate noises. I’ve looked at one figure of 26v/km at latitudes closest to magnetic poles for a near-miss Carrington Event some years ago, which might sound low but makes my skin crawl. At that level, utility lightning arresters wouldn’t open. The only protection would be fuses, reclosers, and lock-out on voltage on neutral and frequency issues – and with harmonics there should be frequency issues. I’m starting to think a Carrington Event would be a relative low voltage (to an electric utility)/high current event.

          While I’m asking for info, here’s a couple of things you might be interested in: Transformer core has a huge effect on GIC damage, with a shell core as the worst and . . . can’t remember . . . as the least. Shell core is an older design and fortunately not a large percentage is out there.

          The other thing is that at 26v/km induced voltage, telegraph lightning arresters probably wouldn’t have arced over. But you have a system designed for 100v – 160v and currents in the milliamp range suddenly subjected to thousands of volts and hundreds of amps. On galvanized iron wire. No wonder sparks flew, operators shocked, and stations burned down. I wonder what temperature that galvanized iron wire reached.

          The 26v/km is likely high, and would have had to been a line running just the right direction at just the right latitude, but it serves as a worst case reference. I’m sure someone’s done it, but if it was known which stations burned down, and which were able to communicate without batteries, and how the lines ran, it may be possible to calculate GIC in the Carrington Event.

          Oh, something else: Telegraphs were connected in series, so it would have been current induced from one end to the other.

    • Bob, we talked about that already. Yes, they vary widely. Generally the more powerful the flare, the bigger the CME, though this is NOT always true — many flares don’t produce a CME at all. They also expand as they move out into the system. Therefore trying to define a density, volume, length, etc. is essentially meaningless, as it will be different at any given point in the planetary system.

  3. 3,520,000,000 lb (1,600,000,000,000 kg).

    One of those has too few or too many zeros.

    I am enjoying this series of posts enough to notice things like that.

    • *sigh* I have a problem with some stuttering keys on my laptop. I have a tendency to go through keyboards like they were made out of tissue paper. My last laptop, I went through something like 3 keyboards, plus two sets of key labels, before we finally gave in and got a new laptop (I needed the upgrade anyway). This laptop has a much more resilient keyboard, but even so, I’m entirely missing the E and the N, and the R, B, F, H, D and A are partly gone. What makes matters worse, however, is that instead of the usual keyboard shape /–\, these keys are inverted \__/, so the crevices between them just collect dust, cat hair, crumbs, and all kinds of trash despite my best efforts, and in order to clean it out properly I need a can of compressed air AND the laptop off and upside-down. Otherwise, the compressed air just blows the junk down into the guts of the keyboard and things stick worse. And while I’ve tried, I don’t seem to have the hang of it.

      Okay, by the looks of things, it stuttered and I didn’t catch it and simply went back and added commas as appropriate. I’ll have to go see what the numbers SHOULD have been. I apologize.

      • By the looks of things, I think I have a few too many zeroes on the kg number. It comes out about right if you whack off the excess.

        • Oooo, nope nope nope. I checked my references. The mass in kg is the correct number. The mass in lb needs more zeroes.
          The correct figures are 3.5×10^12lb or 1.2×10^12kg.

          Sorry for the confusion. The keys stick, either up or down, and if I’m typing at a great rate I may not notice. This is what editors are for. That said, not many editors are gonna check the arithmetic.

  4. I iz confoozed. Is a Coronal Mass Ejection an ejection of Coronal Mass (“a collection of incoherent particles, parts, or objects regarded as forming one body”), or is it a Mass (“done on a large scale or in large quantities”) Ejections from the corona?

    In other words, does Mass modify Ejection or is it modified by Coronal?

    This is why English needs declensions.

  5. YES! More science information! Thank you.

  6. Christopher M. Chupik

    Coronal Mass Ejection would be the name of my band. If I could sing. Or play an instrument.

  7. CME – Continuing Medical Education, or why MomRed had to be at work at 0645 one day a week for [redacted] years, even when on the late shift. Next question?
    *wanders off to read rest of post*

  8. I thought CME stood for “Clinton’s Mendacious Evasions”?

  9. Slightly OT re Stephanie’s last post discussion abou Cosmic Rays, the folks doing the balloon detector flights have updated their chart:

  10. Completely off topic — I am soliciting some cover opinions on my blog:

  11. Great article!

  12. I’m loving this series of posts. Thank you! 😀

  13. Holy cats, guys, I apologize! My days of the week are all off after the Labor Day weekend! I’m here, just very very late! Now let me go read the comments and see what I can do…