Out, Damned Spot! Out, I Say! A Solar Activity Update

By Stephanie Osborn

http://www.stephanie-osborn.com

My experience

I did my graduate work in spotted variable stars at Vanderbilt University, so in the astronomical community I would be considered a variable star astronomer. Based on our experience, many variable star astronomers consider the Sun to be at least borderline variable, and I am one of these. In point of fact, pretty much across the board, astronomers dropped the “solar constant” years ago, because it simply wasn’t. (Unfortunately, other disciplines have not.)

I personally have been watching solar activity for many years now and have watched the activity gradually decrease. As a consequence, I began keeping a rough spreadsheet in summer 2016 as I watched activity begin to drop dramatically. So I have about 2 years of recorded data. It is fairly simplistic, because I only wanted a snapshot and didn’t have time to do more detail, but it serves the purpose, as we will see shortly.

The current solar cycle

This graph is the latter part of solar cycle 23 and all of cycle 24, roughly to date. (Note, however, that the plot ends in ~March 2018. It’s very difficult to find plots that are current to the month.) The red line is the projected curve. The blue line is the smoothed curve. The purple dots and jagged line are the actual data.

Note that the peak for 24 was approximately half that of 23. Also note that we are currently already as low as the minimum that ended cycle 23, at approximately 8.5-9 years into an average-11-year cycle. Theoretically, we still have a couple of years to go before the actual minimum is reached, though 11 years IS an average.

Recent solar cycles

Here is a graph presenting solar cycles 14-24(current). This takes us back to around 1900AD. Note the decrease in the height of the peak (solar max) of each cycle since ~1980. Note the decreased activity in cycle 20. Note the gradual increase in peak height from 1900-1960, though there is a slight drop in cycle 16, around 1930.

Long-term observations

This next chart goes back a LITTLE farther. This is a view of activity over the last 400 years. Note that this graph does NOT include cycle 24; it stops at 23. Cycle 24 is already at roughly the same level as the cycles found in the Dalton Extended Minimum, and this has been noted by several groups with experience in the field.

An interesting correlation

This is a clipping from a Michigan newspaper which was sent to me a couple of months ago. Note the article date written in the margin.

Correlate this to the very low peak of solar cycle 20, which occurred during the 1970s. Note the snow event in 1942, in the cycle subsequent to the diminished cycle 16. Also consider the “Little Ice Age,” which was a prolonged cool period (~1300-1900) overarching the four back-to-back extended minima: the Wolf, Spörer, Maunder, and Dalton Minima (running ~1280-1850AD). Also note the year 1816, the so-called Year Without A Summer, aka “Poverty Year” and “Eighteen Hundred and Froze to Death,” which occurred during the Dalton Minimum (~1790-1830; some argue a later end).

My data (2016)

Legend:

Column 1 is the year.

Column 2 is the month.

Column 3 is the percentage of days in that month with no more than 1 sunspot/sunspot group.

Column 4 is the percentage of days in that month with NO sunspots.

My data (2017)

My data (2018 — incomplete)

My data, graphed (total)

Legend:

The dark green line represents the percentage of days in any given month with no more than 1 numbered sunspot group.

The light green line represents the percentage of days in any given month with no sunspot group.

The latest data

I haven’t had a chance to include the last couple of months of data in the charts as yet. However, in brief synopsis, May had 77.4% of days with no more than 1 sunspot group, and two sets of seven consecutive spotless days. June was much the same, with another spotless week early on; another session of spotless days began June 27^th...and continued through the entirety of July. Today, as I write this, it is July 31^st, and we have had 35 consecutive spotless days. Since it takes about 24.5 days for the solar equatorial regions to rotate once around its axis, this means that we have seen the entire photosphere spotless; not even the solar farside has spots, and this appears to be corroborated by the STEREO solar observing platforms. A couple of short-lived, almost-spot plages developed during this period, on July 3^rd and 21^st, but otherwise there were no visible photospheric features. Virtually the only other solar activity came from the enhanced solar wind streams from coronal holes, and even those are diminishing in size and strength.

Other solar activity

Flare numbers are decreasing; CME numbers are decreasing. BUT cosmic ray flux is increasing. Why? And what do all those words mean, anyway?

Sunspots, flares, and coronal mass ejections (CMEs) are all related; flares tend to produce CMEs, and tend to form near spots. This is because they are all magnetic events. A sunspot is believed to be the “snarl” produced in the magnetic field lines as a result of differential rotation — since the Sun is not a solid body, it does not rotate uniformly; rather, it follows Kepler’s Laws of orbital motion. The poles rotate faster than the equator, and the interior rotates faster than the photosphere. But since it is a plasma body, and plasma is composed of charged particles, it generates a strong magnetic field. As this differential rotation proceeds, the field lines gradually wrap up. If (among other things) local inhomogeneities occur, the field strength can vary, and the field lines may “snarl.” But they also tend to move upward as the plasma convects. When the snarls reach the photosphere — the visible surface — they are slightly cooler, hence darker, and appear as sunspots.

But these snarls contain carp-tons of magnetic potential energy. And from time to time, that potential energy manages to release itself, in the form of a magnetic reconnection event. This is, in essence, the field trying to simplify itself and untangle, after a fashion — the field lines break here and reattach over there, in an effort to reshape themselves and eliminate the snarl. This converts the potential energy into tremendous amounts of other kinds of energy — thermal and kinetic, to name a couple — and the result is a flare. This explosive event can — but does not always — then generate the equivalent of a mushroom cloud, which blows off the photosphere into the solar system, accelerated by the reconfiguring magnetic fields. This “mushroom cloud” is the CME.

Given that this differential rotation creates an extremely complex overall magnetic field, sometimes field lines leave the Sun and stretch off — essentially to infinity — in places not normal for a typical dipole (bar) magnet, which ordinarily would mean JUST the poles. These regions of “infinite field lines” are visible in certain wavelengths of light as darker regions, due to the relative lack of plasma in the inner corona, and they are called coronal holes. The solar wind tends to be “enhanced” along these field lines, since the magnetic field is effectively accelerating the plasma in these regions. They are strong, and can create minor geomagnetic storming and aurorae on Earth (or the other planets) if we pass through that enhanced wind stream, but it won’t be as strong as getting hit with a big CME.

Cosmic rays are generally subatomic particles of various sorts, originating from outside our solar system — sometimes outside our galaxy. They are extremely energetic and are produced by the more powerful cosmic objects out there: pulsars, magnetars, supernovae, black hole accretion disks, even quasars. They can be dangerous precisely because they are so energetic, and often if they hit an object, they produce a cascade of additional particles. (In atmosphere, this is called a cosmic ray shower.)

BUT, since most of them are charged particles — they’d be incredibly hot plasma if you got enough of ‘em together in one place — they can be deflected by magnetic fields. And woo-ha, a moving plasma such as the solar wind constitutes a current, which in turn generates an interplanetary magnetic field! So this magnetic field protects the inner solar system from potentially deadly cosmic radiation. (The term “flux” simply means you’re measuring the number of such particles passing through a given area — typically a square meter — per second.)

So. The stronger the interplanetary magnetic field, the better the protection we have from cosmic rays, and the lower the cosmic ray flux will be.

BUT.

When the Sun is less active, the slower and less dense the solar wind will be, hence the weaker the interplanetary field will be.

So we would expect that an active Sun would mean a low cosmic ray flux, and an inactive Sun would mean a higher cosmic ray flux...and this is exactly what we see. More, as the solar activity has diminished in recent years, we have watched the cosmic ray flux increase.

Credit: graph from spaceweather.com

Note: Stratospheric flux tends to be more representative of solar system fluxes than lower-altitude measurements; this is because the atmosphere attenuates the rays. Note how the flux has increased from 78x to 88x that found at sea level.

My thoughts

Based on all this information, it is my considered opinion that we are about to enter an extended minimum, if we are not already in one. The double-dynamo solar model predicted one more solar cycle before entering an extended minimum. However, this model, while able to accurately recreate the shapes of recent solar cycles, has been unable to adequately model historic extended minima. It must therefore be concluded that it is not complete. It is my educated conclusion that it does not go far enough, and there is at least one more dynamo which needs to be modeled. It is therefore likely that the onset and the exit of the predicted extended minimum may be “squishy,” and the dates may vary by as much as a solar cycle or more.

It is very true that “correlation does not equal causation,” but when correlations begin to mount, it is foolhardy to refuse to consider the possibility of a coupling mechanism. To name a few correlations:

·         Greenland/Vinland settlement around 1000AD/tail end of the Roman Warm Period

·         The Little Ice Age/four consecutive extended minima

·         The Year Without A Summer/Dalton Minimum

·         Snow in summer in 1942/low-activity Cycle 16 preceding

·         Snow in summer in 1979/low-activity Cycle 20 preceding

·         Modern Warm Period/increasing solar activity in 1st half 20th Century

·         Plateau in warming in the 2000’s/gradual decrease in solar activity since ~1980

Yes, certainly volcanic eruptions and other events factor into the situation. But how many correlations does it take before we need to sit up and take notice? Before we seriously start to wonder what is really going on?

For more on solar activity, check out The Weather Out There Is Frightful , by Stephanie Osborn. 

Space Weather - The Carrington Event

In August of 1859, during historic Solar Cycle 10, something very strange began to happen. The Sun, as it neared solar max, grew unusually active. It produced prolific numbers of sunspots and flares, some of which were visible to the naked eye. This continued through the end of the month, until, just before noon on September 1, British astronomer Richard Carrington, just 33 and already acknowledged as one of England's premier solar astronomers, observed an incredibly brilliant solar flare – a flare that was easily visible to the naked eye. In later times, this single flare became known as The Carrington Super-Flare. In his own words from his scientific records:

“...Within the area of the great north group [of sunspots]...two patches of intensely bright and white light broke out...My first impression was that by some chance a ray of light had penetrated a hole in the [projection] screen...for the brilliancy was fully equal to that of direct sun-light; but by at once interrupting the current observation, and causing the image to move by turning the R.A. [right ascension, an astronomical coordinate akin to longitude] handle, I saw I was an unprepared witness to a very different affair...The instant of the first outburst was not 15 seconds different from 11h 18m Greenwich mean time, and 11h 23m was taken for the time of disappearance [from the telescope's view]. In this lapse of 5 minutes, the two patches of light traversed a space of about 35,000 miles...”

British amateur astronomer Richard Hodgeson also observed it; Balfour Steward at the Kew Observatory noted a “crochet” effect on the observatory's magnetometer. (A “crochet” is also sometimes called a Sudden Ionospheric Disturbance, or SID. It is when a solar event produces an abnormally high plasma density – remember, plasma is like the stuff in your fluorescent lights – in one layer of the ionosphere. This in turn creates literal electric currents running through the ionosphere, which magnetometers pick up. It creates something of an invisible lacy pattern in the atmosphere, hence, I suppose, the term “crochet.”)

And all of the previous flares and coronal mass ejections had fairly effectively cleared the interplanetary medium between the Sun and Earth.

The enormous coronal mass ejection produced by the super-flare slammed into Earth in only 17 hours.

The resulting effects lasted several days.

What kind of effects?

Worldwide aurorae for starters. These aurorae were most noted in the Caribbean, where they had never been seen before. Colorado gold miners, awakened by the brightening skies, got up and began cooking their breakfasts, because they thought it was dawn. In Europe and the northeastern United States, newspapers could be read by the light of the aurorae.

Speaking of newspapers, the Baltimore American and Commercial Advisor spoke of the ongoing event in poetic terms. “Those who happened to be out late on Thursday night had an opportunity of witnessing another magnificent display of the auroral lights. The phenomenon was very similar to the display on Sunday night, though at times the light was, if possible, more brilliant, and the prismatic hues more varied and gorgeous. The light appeared to cover the whole firmament, apparently like a luminous cloud, through which the stars of the larger magnitude indistinctly shone. The light was greater than that of the moon at its full, but had an indescribable softness and delicacy that seemed to envelop everything upon which it rested. Between 12 and 1 o'clock, when the display was at its full brilliancy, the quiet streets of the city resting under this strange light, presented a beautiful as well as singular appearance.”

Those dealing in the business of telegraphy did not think so highly of the display. The incredibly intense event, a maximal G5 and S5 by any definition, created induced currents in telegraph wires that were simply impossible to control. Lines and pylons threw sparks, telegraph batteries were blown, telegraphers received severe shocks, and telegraph “flimsy” paper burst into flames.

And yet some telegraph systems continued to function, despite having no batteries to power them. The induced current was simply that strong.

This was the Carrington Event, the most powerful solar/geomagnetic storm ever to occur in recorded history. It was before the advent of electricity, or electronics, or integrated grids and networks, save for telegraph systems, with which it wreaked havoc. Imagine what effect it would have today.

Dibs on the story.    ;-)

-Stephanie Osborn

http://www.stephanie-osborn.com

Solar-Earth DefCon Levels, Part 2

Now, while all of this stuff is going on in the geomagnetic field, what's happening in space? Hard radiation, and lots of it, that's what. After all, that's basically what's causing the disturbance in the geomagnetic field.

And of course NOAA has another scale that relates to that, called the solar storm scale, and represented by – you guessed it – S.

There's not a direct correlation that I've ever been able to find between the G scale and the S scale, because the S scale is determined by the number of protons of a given energy that passes through, say a square meter in a second. This number is called the proton flux. (In the case of the S scale, the energy of the protons must be greater than or equal to 10MeV, where MeV is mega-electron-volts. An electron volt is very tiny, only 1.6x10^-19 joules. So an MeV is an energy of 1.6x10^-12 joules. It's not big, but when you're talking about something as small as a proton, it's big enough.)

So at S1, our proton flux is 10 protons per second per steradian per square centimeter. (This is not a very big area. The bigger the number of protons passing through, the bigger the radiation dose.) An S1 is a minor solar storm. According to NOAA, the effects are as follows, “Biological: none. Satellite operations: none. Other systems: minor impacts on HF radio in the polar regions.” This happens a lot, but not quite as often as a G1 – an S1 occurs about 50 times per solar cycle.

An S2 is a moderate solar storm. It requires a proton flux of 100, and occurs half as often as an S1. Effects: “Biological: passengers and crew in high-flying aircraft at high latitudes may be exposed to elevated radiation risk. Satellite operations: infrequent single-event upsets possible. [A single-event upset, or SEU, is when the bit of a computer is accidentally reset to its opposite condition by a proton or electron impact.] Other systems: small effects on HF propagation through the polar regions and navigation at polar cap locations possibly affected.”

S3 is a little stronger still; it's a “strong” solar storm, with a proton flux of 1000. (Note that the solar storm scale is a logarithmic scale like the Richter scale, with each step of the scale having 10x greater proton flux than the previous.) Only 10 of these typically occur per solar cycle, but they aren't pleasant. “Biological: radiation hazard avoidance recommended for astronauts on EVA; passengers and crew in high-flying aircraft at high latitudes may be exposed to radiation risk. Satellite operations: single-event upsets, noise in imaging systems, and slight reduction of efficiency in solar panel are likely. Other systems: degraded HF radio propagation through the polar regions and navigation position errors likely.”

Stepping up to an S4, a severe solar storm, we have a proton flux of 10,000. They are pretty rare, with only about 3 per solar cycle occurring. “Biological: unavoidable radiation hazard to astronauts on EVA; passengers and crew in high-flying aircraft at high latitudes may be exposed to radiation risk. Satellite operations: may experience memory device problems and noise on imaging systems; star-tracker problems may cause orientation problems, and solar panel efficiency can be degraded. Other systems: blackout of HF radio communications through the polar regions and increased navigation errors over several days are likely.”

And finally the granddaddy of solar storms, the S5, the extreme storm. It has a proton flux of 100,000 protons per second per steradian per square centimeter. Simply put, a flood of 100,000 protons is striking every square centimeter (less than half an inch each way), every second. These are very rare, and may or may not occur in any given solar cycle. But they can be devastating. “Biological: unavoidable high radiation hazard to astronauts on EVA (extra-vehicular activity); passengers and crew in high-flying aircraft at high latitudes may be exposed to radiation risk. Satellite operations: satellites may be rendered useless, memory impacts can cause loss of control, may cause serious noise in image data, star-trackers may be unable to locate sources; permanent damage to solar panels possible. Other systems: complete blackout of HF (high frequency) communications possible through the polar regions, and position errors make navigation operations extremely difficult.”

We're fortunate those don't occur very often at all.

But even the typical description of a G5 or S5 doesn't match the strongest geomagnetic storm in history.

-Stephanie Osborn

http://www.stephanie-osborn.com

Solar-Earth DefCon Levels, Part 1

As I told you last week, NOAA has a scale of geomagnetic activity that ranges from G0 to G5, where G0 is quiescent, and G5 is the worst geomagnetic storm around. Now, we've already talked a little bit about what geomagnetic storms do...

No, we didn't, you say?

Ah, but we did. Back when I told you about all the effects that Coronal Mass Ejections can have. (Solar, Space, and Geomagnetic Weather, Part 4.) Because those sorts of things are what cause the geomagnetic storms.

But probably the best way I can tell you about the effects is simply to quote from NOAA's scale itself (which can be found here: http://www.swpc.noaa.gov/NOAAscales/#GeomagneticStorms).

As I mentioned last week, a G0 is the normal, quiescent geomagnetic field. This holds until the Kp index reaches 5, and then we begin minor geomagnetic storming, with the scale hitting G1. According to NOAA, “Power systems: weak power grid fluctuations can occur. Spacecraft operations: minor impact on satellite operations possible. Other systems: migratory animals are affected at this and higher levels; aurora is commonly visible at high latitudes (northern Michigan and Maine).” These are fairly frequent, with on average close to 2000 per 11-year solar cycle.

At Kp=6, G2 is considered a moderate storm. “Power systems: high-latitude power systems may experience voltage alarms, long-duration storms may cause transformer damage. Spacecraft operations: corrective actions to orientation may be required by ground control; possible changes in drag affect orbit predictions. Other systems: HF radio propagation can fade at higher latitudes, and aurora has been seen as low as New York and Idaho (typically 55° geomagnetic lat.).” These are a little less frequent than G1, but still occur at a rate of about 600 every solar cycle.

When Kp=7, G3 is a strong geomagnetic storm. “Power systems: voltage corrections may be required, false alarms triggered on some protection devices. Spacecraft operations: surface charging [static electricity buildup; this can lead to arcing]may occur on satellite components, drag may increase on low-Earth-orbit satellites, and corrections may be needed for orientation problems. Other systems: intermittent satellite navigation and low-frequency radio navigation problems may occur, HF radio may be intermittent, and aurora has been seen as low as Illinois and Oregon (typically 50° geomagnetic lat.).” These are less frequent still, with on average 200 per solar cycle. Also, as the geomagnetic storms increase in strength, their likelihood of occurrence tends to concentrate around solar maximum, though this is not a hard and fast rule.

At Kp=8, G4 is a severe geomagnetic storm. “Power systems: possible widespread voltage control problems and some protective systems will mistakenly trip out key assets from the grid. Spacecraft operations: may experience surface charging and tracking problems, corrections may be needed for orientation problems. Other systems: induced pipeline currents affect preventive measures, HF radio propagation sporadic, satellite navigation degraded for hours, low-frequency radio navigation disrupted, and aurora has been seen as low as Alabama and northern California (typically 45° geomagnetic lat.). These are rarer still, with only about 100 seen per solar cycle.

And then there's the big boys. Kp=9 means a G5 extreme geomagnetic storm. “Power systems: widespread voltage control problems and protective system problems can occur, some grid systems may experience complete collapse or blackouts. Transformers may experience damage. Spacecraft operations: may experience extensive surface charging, problems with orientation, uplink/downlink and tracking satellites. Other systems: pipeline currents can reach hundreds of amps, HF (high frequency) radio propagation may be impossible in many areas for one to two days, satellite navigation may be degraded for days, low-frequency radio navigation can be out for hours, and aurora has been seen as low as Florida and southern Texas (typically 40° geomagnetic lat.).” These are the rarest of all, but still occur on average 4 per solar cycle.

-Stephanie Osborn

http://www.stephanie-osborn.com

Solar Activity and the Activity Indices

Okay, back to bar magnets again. Because the Earth has one. But of course it's three-dimensional, not like our iron filings on paper example. Imagine picking up the bar magnet with the iron filings and paper attached, and rotating it 360º, letting the iron filings remain in the areas they move through. Now you have an image of what a three-dimensional dipolar (2-pole) magnetic field looks like – sort of like a giant pumpkin. With the solar wind (which is probably the largest influence on the interplanetary magnetic field) pushing on it from the Sun direction, the side of the pumpkin facing the Sun tends to smush in, but the side away from the Sun tends to stretch out and form a long tail. (You can see a really good animation of how this works here: http://en.wikipedia.org/wiki/File:Animati3.gif) This is all to say that you HAVE to think of the geomagnetic field three-dimensionally. And if it is three-dimensional, then each part of the field has an x-, a y-, and a z-coordinate component.

Let's simplify for a minute. Let's say that we're going to look at the component of the geomagnetic field that is running horizontally to the Earth's surface at any given point. Now because the Earth is curved, this is a tangent line that is continually changing as you move around the Earth. Now let's look at the disturbances from normal, caused by solar weather – coronal holes, CMEs, what have you.

So we have these variations, that are going to be different for different parts of the Earth for the same event. How do we measure it? It's a little like a Richter scale for geosolar storms. It runs from zero to nine, and there's a special formula that enables it to be calculated regardless of the location of the observatory, just like the Richter magnitude of a quake can be determined from seismographs on the opposite side of the globe. This scale for solar-induced geomagnetic activity is called the K-index. Zero is essentially no activity; anything above 5 is considered a storm level of activity. The bigger the number, the greater the effects seen on the ground, and the farther south the auroral oval can be seen. At a K=9, the aurora can be seen...in the TROPICS.

(Just for the sake of more information, the letter K was derived from the German word “kennziffer,” which apparently means “characteristic number.” Us scientists, we love our imaginative names, you know?)

Now if we reference the Kp index, we're talking about the interplanetary K index, not the geomagnetic K index. This is an average of all the K indices from all of the observatories, weighted as appropriate (remember, you won't get the same measurements from the various observation sites, so you have to factor that in, as well as the fact that the geomagnetic field is constantly changing). This gives us an indication of what the interplanetary magnetic field (IMF) is doing. BUT – not all of the stations report in at the same time. So then scientists have to calculate something called the “estimated Kp” which is just what it sounds like – an estimate for those stations that haven't reported in yet. This can sometimes be a very good predictor of what the magnetic field is going to do, and sometimes not so much. We're still very much learning this particular science.

But we're not done with indexes. There's also something called the a index. This is based on the AMPLITUDES (yep, there's the reason for using an a) of the deviations from geomagnetic normal, taken over a three-hour period. Then there's the A index, which is an AVERAGE (yep, that's where the A came from) of all the a-indices for a 24-hour period.

One more index we need to look at is the G scale, which is the National Oceanic and Atmospheric Administration's (NOAA) way of quantifying the strength of the geomagnetic disturbance. For any K index of 4 or less, the scale shows G0. At K=5, we jump to G1 – minor storming. For K=6, we have G2. For K=7, G3. At K=8, we have a storm level of G4, and at the maximum K=9, we have maximum storming of G5. Think of it like the Earth's solar DefCon level.

Next week we'll go into those DefCon levels in detail.

-Stephanie Osborn

http://www.stephanie-osborn.com

Solar, Space, and Geomagnetic Weather, Part 4

So what the heck are CMEs?

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.

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?)

The vast majority of them aren't THAT big, and aren't even Earth-directed. The chances of one smacking Earth aren't that big. 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.

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. 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 trillion 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 fast CME can reach Earth in just under 13 hours.

-Stephanie Osborn
http://www.stephanie-osborn.com

Solar, Space, and Geomagnetic Weather, Part 3

So what are the effects of coronal hole winds and Coronal Mass Ejections (CMEs)?

They 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.

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 electicity. Remember how I said, in part 1, 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.

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 it causes the aurorae. Most of you reading this have heard of the Northern Lights, properly termed the Aurora Borealis, but there are also the Southern Lights, the Aurora Australis. 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.) They are 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.

-Stephanie Osborn
http://www.stephanie-osborn.com

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
http://www.stephanie-osborn.com