Seven [SOLAR] Days in May

This is a very good annotated discussion from one of the resident solar experts on the QRP-L Email list. It is an entire primer on solar events, how to read solar activity reports, what to expect, where geomagnetic storms come from etc. It details a recent series of events that caused HF blackout conditions and some of the most intense Geomagnetic storming in a decade. It is a slow, but very worthwhile read:

Maile

Date: Tue, 5 May 1998 22:51:06 -0600 (MDT)
From: Paul Harden
To: "Low Power Amateur Radio Discussion" [QRP-L]
Subject: SOLAR STORM UPDATE MAY 05

Actually, the subject is misleading since we're in a GEOMAGNETIC storm, the AFTERMATH of the long-gone solar storm. And because I've discussed the specifics of this event, I have neglected the "big picture" on all of this from the email I've received, so will briefly correct that here:

THE SOLAR STORMS that started all of this was a big X-class flare last Thursday, and two more X-class flares Saturday. In very simplistic terms, these were an explosion of solar mass on the sun's surface. At the moment of the disturbance, high energy from X-rays down to HF were emitted DURING the disturbance (which lasted about 8 minutes each on Saturday). This produced about 20 minutes of strong, bursty static ... the first part of the SOLAR storm.

This explosion threw mass (heavy electrons) into the solar atmosphere, not unlike the mushroom cloud of an atomic bomb. Many of these electrons get "trapped" in the sun's magnetic field and begin to spiral along the magnetic field lines ... generating RF energy from about 800MHz downward ... in this case to about 20 MHz. This is called a TYPE III STORM you saw mentioned in the initial report. The RF sweeps downward in frequency about 20MHz per second, so if you were in a QSO, this TYPE III sweep would sound like a big burst of static at regular intervals, almost like ignition noise.

As this "mushroom" cloud rises from the sun, it also must pass through the sun's magnetic field lines. This mass of electrons and protons, traveling through a magnetic field produces electricity. These electric currents also produce radio energy, but over a very wide band of frequencies simultaneously, producing wide band noise on earth. This is called CONTINUUM RADIATION, or a TYPE IV STORM, also reported on Saturday's report. On earth, it is an elevation of noise over much of the HF spectrum.

The TYPE III storm lasts about 10-20 minutes following the solar disturbance, while the TYPE IV persists about an hour. Therefore, the actual SOLAR STORM is relatively short in duration, typically less than an hour of bursting static, Type III sweeps and elevated noise. And generally, such a disturbance will elevated the solar flux.

Now then ... the solar storm is over. But this "shock wave" of electrons and protons continues to travel away from the sun and will continue to travel into interplanetary space. If the trajectory is right, it can smack right into the earth, triggering a GEOMAGNETIC storm. Thus, not all big flares will necessarily cause a geomagnetic storm.

THE GEOMAGNETIC STORMS we've experienced past few days is the result of this "shock wave" smacking into the Earth. How lucky can we get? The magnetic field surrounding the earth looks like a torpedo, with the blunt end (the head) facing the sun, and the tail extending away from the sun far past our moon. As the earth travels around the sun plowing through the solar wind, this blunt side of our magnetic field becomes the earths "bow shock" wave of sorts ... a definite boundary where our magnetic field begins.

The earth sits inside our magnetic field like a cocoon, and it is quite fragile. About 2-3 days after Saturday's X-flares, this shock wave of protons is first detected by the ACE satellite, and about 30 minutes later it smacked into the earths magnetic field just like a big gust of wind. This caused our magnetic field to wiggle and tremble like it was a sphere of Jello.

(I got email from some DX stations wanting to know what Jello is. It is a gelatin desert, or akin to jelly or a stiff pudding).

As our magnetic field trembled, it generated electric currents due to the "dynamo" effect. These electric currents generate gobs of radio emission in the form of wide-band, or continuum static ... making the noise levels on HF very high.

Additionally, these electrons/protons travel along our magnetic field and fall inwards into our ionosphere at the polar regions, where the field is the weakest. Here the electrons tend to bunch up on the D-layer, making it very dense, and thus, difficult for radio signals to pass through to get to the E and F layers. The D-layer is often called the "absorption layer" because it absorbs much of the RF trying to get through it. Of course it CAN absorb all RF trying to get through it, shutting down all "skip" propagation. Certainly you've observed this effect the past two days :-)

Other factors determine how the D-layer is charged, then depleted of these extra electrons, such that this absorption can tend to "come and go" during the geomagnetic storm. Of course keep in mind, with a large solar disturbance, these electrons/protons keep getting pumped into the earth at the poles for many hours (some times for days), keeping this condition active for hours or days.

So while "legally" the maximum usable frequency (MUF) may indeed be quite high, HF signals are highly impeded trying to get through the D-layer. A MUF above 100MHz is not unusual. Now VHF frequencies can penetrate the D-layer relatively easy. This is why after a solar storm and during a geomagnetic storm, HF may be shut down, but on the other hand, you can pick up very distant FM or TV stations, because those signals are skipping off the highly ionized E and F layer. The D-layer normally absorbs RF below about 30 MHz (and in fact, is what determines the lowest usable frequency, or LUF). Normally the LUF is about 2 MHz; in a geomagnetic storm, it can be 30 MHz. That would be a "black out" ... which many of you also experienced.

Maile

SUMMARY:

Maile

Now to "Dissect" Today's Solar/Geophysical Report:

(Portions omitted)


JOINT USAF/NOAA REPORT OF SOLAR AND GEOPHYSICAL ACTIVITY

SDF NUMBER 125 ISSUED AT 2200Z ON 05 MAY 1998

IA.  ANALYSIS OF SOLAR ACTIVE REGIONS AND ACTIVITY FROM 04/2100Z
TO 05/2100Z: SOLAR ACTIVITY HAS BEEN LOW. 

THIS REGION IS GROWING AND HAS BRIGHT PLAGE WITH FREQUENT
FLUCTUATIONS.

Plage are the "globs" of slightly darker matter all over the solar surface. A brightening of plage in an area often precedes a disturbance. This correlation is not yet well understood.


OBSERVERS ARE REPORTING GROWTH AND DEVELOPMENT OF PENUMBRA
IN THE INTERMEDIATE SPOTS.

A close-up view of sun spots will sometimes show tiny filaments, like little fingers, sticking outward around the sun spots. One of the theories is these particular sun spots are the top of a magnetic "shaft." Magnetic lines come out of the shaft (the spot) and re-enter the sun in the form of hundreds of small field lines. Kind of like a garden sprinkler, with a column of water shooting upward, but falls to the ground in an omnidirectional pattern of hundreds of little streams. The burning surface of the sun tends to bunch up between these hundreds of little field lines, cooling, and optically appear to be dark filaments.

Regardless of the mechanism, it IS indicative of a developing magnetic field around the sun spots, which can often jump over to another sunspot, and a bunch of magnetic fields, all criss-crossing start to develop. This "complexity" pattern often precedes a major disturbance.


THE CURRENT MAGNETIC CONFIGURATION IS MORE COMPLEX TODAY
(BETA-GAMMA) AND THE REGION IS BECOMING COMPACT. 

This "complexity" means the magnetic fields are becoming bipolar, that is a north pole coming out of one spot, and a south pole as it re-enters another (Beta-Gamma group defines the N-S polarization is observable). The more compact the region gets, the stronger the magnetic field becomes, which appears to trigger a disturbance by "sucking" hot burning mass from below the surface, hurling it outward into space ... a FLARE.


IB.  SOLAR ACTIVITY FORECAST:  SOLAR ACTIVITY IS EXPECTED TO BE
MODERATE. THERE IS A GOOD CHANCE FOR AN M-CLASS EVENT FROM REGION
8214.

The region (8214) of magnetic "complexity" described above.


THERE IS ALSO A POSSIBILITY FOR A MAJOR FLARE FROM THIS REGION,
ESPECIALLY IF THE CURRENT TRENDS CONTINUE.

See. And you thought I was making all of this up, huh?

The point to remember ... this possible new solar disturbance has nothing to do with our current geomagnetic storm. Should another major flare occur, the entire sequence will start all over again!!!

The following GEOMAGNETIC discussion DOES refer to what's going on now:


IIA.  GEOPHYSICAL ACTIVITY SUMMARY FROM 04/2100Z TO 05/2100Z:

THE GEOMAGNETIC FIELD HAS RANGED FROM UNSETTLED TO MAJOR STORM
LEVELS OVER THE PAST 24 HOURS ... WITH MAJOR STORM CONDITIONS
OBSERVED AT MID AND HIGH LATITUDE STATIONS.

FROM 0700-2100Z THE FIELD HAS BEEN CHARACTERIZED BY PREDOMINANTLY
ACTIVE LEVELS, WITH SOME MINOR STORM PERIODS AT THE HIGH LATITUDE
STATIONS.

THE CURRENT ACTIVITY IS ASSOCIATED WITH THE X1/3B/HALO CME EVENT
OF 02/1342Z. THIS EVENT WAS INITIALLY SEEN AT ACE AS A STRONG
SHOCK AT 04/0229Z FOLLOWED BY A PERIOD OF NEGATIVE BZ
FROM 04/0230-0430Z.

Bz is a measure of the direction and intensity of the magnetic field in the solar wind area, that is, outside the earths magnetic field.


THE SOLAR WIND DATA HAVE CONTINUED TO SHOW CHARACTERISTICS OF
TRANSIENT FLOW OVER THE PAST 24 HOURS, NAMELY STRONG MAGNETIC
FIELDS, VARIABLE TEMPERATURES, AND VARIABLE BUT HIGH
VELOCITIES. THE FLOW DOES NOT SHOW THE 'CLASSIC CLOUD' STRUCTURE,
SUGGESTING THAT THE DRIVER MISSED HITTING THE EARTH DIRECTLY.

This is saying while the shock wave of the solar disturbance did hit us, the "bulk" or core of the ejected mass of electrons/protons did not. In other words, this storm could have been much, much worse!


THE GREATER THAN 2 MEV ELECTRONS EXCEEDED HIGH LEVELS DURING
THE PAST 24 HOURS.

This has to do with the electron density and strength outside our ionosphere and WHERE MOST OF OUR SATELLITES ARE LOCATED. This has nothing to do with HF communications on earth, but would be of high concern if you owned one of those satellites! It is mostly a warning for the operators of satellites that high electron density is occurring, which could cause electrical failures in the electronic equipment onboard the satellites. (2 MEV = 2 Million Electron Volts.)

I truly believe that before this solar cycle is over, there will be several notable satellites destroyed by the effects of a solar storm. The GPS satellites, for example, are made of radiation hardened components to withstand this sort of thing, but many are not.


IIB.  GEOPHYSICAL ACTIVITY FORECAST:  THE GEOMAGNETIC FIELD IS
EXPECTED TO BE PREDOMINANTLY ACTIVE FOR THE NEXT 24-36 HOURS DUE
TO LINGERING EFFECTS OF THE CURRENT DISTURBANCE. CONDITIONS
SHOULD RETURN TO UNSETTLED TO QUIET THEREAFTER.

Of course if another major flare occurs tomorrow or Thursday, it will change this picture in a hurry for more geomagnetic storming by this weekend.


III.  EVENT PROBABILITIES 06 MAY-08 MAY

CLASS M    75/75/75 --- a 75% chance of an M-class (fairly large)
CLASS X    20/20/20     over the next three days.
PROTON     20/20/20
PCAF       YELLOW   --- Polar Cap Absorption warning

IV.  PENTICTON 10.7 CM FLUX

OBSERVED           05 MAY 133
PREDICTED   06 MAY-08 MAY  135/135/130
90 DAY MEAN        05 MAY 106

V.  GEOMAGNETIC A INDICES

OBSERVED AFR/AP 04 MAY  090/096  --- a MAJOR storm (50-100)
ESTIMATED AFR/AP 05 MAY  025/035 --- a MINOR storm (29-50)
PREDICTED AFR/AP 06 MAY-08 MAY  020/025-015/020-005/013
                                 ^^^^^   ^^^^^   ^^^^^
                                  Wed.    Thurs   Fri.

Leveling off fast. Still noisy, but HF communication paths will be open, and friday is about normal. Although these effects will tend to linger a bit longer in the higher latitudes, like Alaska.

I'm sorry for this being so lengthy, but it seemed it would be far less effective of an explanation to break it up into installments. Particularly with it all "fresh on our minds."

You have all experienced first hand the first major geomagnetic storm in a decade. And other than just experiencing the bands being dead, many of you have appreciated the physics and mechanisms behind it, making those of you who have bothered to read this far, some of the most informed amateurs on the face of the earth.

Seriously, as much of this has all developed from very recent observations of the sun, and very little of it has appeared yet in printed form. But I must give public credit to Dr. Tim Bastian, our observatory staff solar astronomer, for eagerly explaining those concepts where my own knowledge level craps out. In short, you're getting this (albeit 2nd hand) from one of the world's premier solar astronomers. And as current as yesterday afternoon :-)

Hope you enjoyed it. More to come as dictated by the sun.


72, Paul NA5N



Date: Thu, 7 May 1998 01:19:01 -0600 (MDT)
From: Paul Harden <pharden@aoc.nrao.edu>
To: "Low Power Amateur Radio Discussion" [QRP-L]
Subject: ANOTHER SOLAR STORM ALERT MAY 6

The sun produced THREE major flares again today, two M-class and an X-class, with 3 CME's. This means more VERY SERIOUS geomagnetic storming is very likely Saturday and Sunday. And these did NOT come from the two areas of the sun where major flare development is being watched. The geomagnetic storm, however, appears to be over.

BEST QRP CONDITIONS are probably right now through Friday night with solar flux at 130 and high MUF's, AND before the next geomagnetic storm hits (late Friday or early Saturday).

If you're a 6M/UHF freak, conditions are also good right now and may continue to be through the weekend, as your window is above the geomagnetic storm to take advantage of a very high MUF.

And lastly, with things already charged up, this new solar activity could produce some spectacular auroras, even into the middle latitudes. (I have not looked up the auroral forecast yet).


JOINT USAF/NOAA REPORT OF SOLAR AND GEOPHYSICAL ACTIVITY
SDF NUMBER 126 ISSUED AT 2200Z ON 06 MAY 1998

IA.  ANALYSIS OF SOLAR ACTIVE REGIONS AND ACTIVITY FROM 05/2100Z
TO 06/2100Z:  SOLAR ACTIVITY WAS HIGH. REGION 8210 (S15W75)
PRODUCED AN X2/1N FLARE AT 0809Z WHICH HAD VERY STRONG ASSOCIATED
RADIO BURSTS AND A TYPE IV RADIO SWEEP.

Gads, this is the 4th x-class flare in a week. Remember the Type IV sweep ... continuum noise over a huge chunk of the spectrum caused by VERY energetic activity from this disturbance.


REGION 8210 ALSO PRODUCED AN M2/2N FLARE AT 05/2346Z WHICH HAD
ASSOCIATED TYPE II AND TYPE IV SWEEPS.

A TYPE II sweep is similar to the Type III, except is sweeps downward in frequency about 2 MHz/sec. (the Type III is about 20 MHz/sec). Type II's sound like "swishes" or "splashes" of static.


LASCO OBSERVERS REPORTED THREE CORONAL MASS EJECTIONS DURING THE
TIME PERIOD: THE FIRST WAS A PARTIAL HALO AT 0002Z AND COULD BE
REASONABLY ASSOCIATED WITH THE M2/2N. 

A partial halo CME means it was a "finger" of mass ejection, and did not loop back into the sun. Still, capable of throwing gobs of particle radiations towards us to trigger a geomagnetic storm. (Trajectory is not yet known).


THE SECOND WAS AT 0228Z FROM THE NORTH EAST AND APPEARS TO BE
AN EVENT BEHIND THE LIMB. 

A CME behind the limb (i.e., not on the surface visible from the earth) means the mass is flying away from the earth and this CME will not effect us.


THE THIRD, SEEN AT 0829Z WAS A LARGE AND RELATIVELY FAST EVENT THAT
APPEARS TO BE ASSOCIATED WITH THE X2 FLARE.

This also could effect the earth if the trajectory is right, and since the particle radiation from a large flare (like an x-class) fans out, we would be VERY lucky if it missed us. Brace yourselves for awful conditions Saturday or so.


REGION 8214 (N28W34) HAS NOT BEEN IMPRESSIVE IN TERMS OF FLARE
PRODUCTION,

This is the area discussed yesterday where the magnetic complexity was building and showing potential for a large flare. Oddly, today's X and M class flares didn't even come from this region. Oh oh ... we may be in big trouble if this region goes active too.


BUT IT CONTINUES TO GROW IN COMPLEXITY AND CONTINUES TO DISPLAY
VERY HOT PLAGE. SOME OPPOSITE POLARITY FLUX IS EMERGING JUST WEST
OF THE LEADER SPOT, AND THIS PART OF THE GROUP APPEARS TO BE THE
'HOT SPOT'

Remember yesterday's discussion about how the magnetic field lines around sun spots can become bipolar ... often preceding a disturbance? Here the opposite polarity (N and S poles) have been observed. The "leader spot" is the one described yesterday as the one developing on top of the "magnetic shaft," or the source of the magnetic field lines.


IB.  SOLAR ACTIVITY FORECAST:  SOLAR ACTIVITY IS EXPECTED TO BE
MODERATE. THERE CONTINUES TO BE A FAIR CHANCE FOR MORE MAJOR FLARES,
PRODUCING M-CLASS EVENTS AND SOME POSSIBILITY FOR MAJOR FLARES OR
PROTON EVENTS.

Friends ... this is NOT looking good!!!


IIA.  GEOPHYSICAL ACTIVITY SUMMARY FROM 05/2100Z TO 06/2100Z:

THE GEOMAGNETIC FIELD HAS BEEN QUIET TO UNSETTLED.

The current geomagnetic storms appears to be over. But now the bad news ...


IIB.  GEOPHYSICAL ACTIVITY FORECAST:  THE GEOMAGNETIC FIELD SHOULD
BE MOSTLY UNSETTLED UNTIL THE POSSIBLE ARRIVAL OF EFFECTS FROM THE
LEADING EDGE OF TODAY'S CME EVENTS ASSOCIATED WITH REGION 8210. THE 
LATER CME WAS SUFFICIENTLY FAST THAT IT WILL VERY LIKELY OVERTAKE THE
EARLIER CME. ARRIVAL OF THE SHOCK IS EXPECTED VERY LATE ON THE 7TH
OR EARLY ON THE 8TH, AND A PERIOD OF STRONG ACTIVITY IS LIKELY

If the later CME shock wave is traveling fast, and hits the earth (very likely), it will whomp us good.


SHORTLY THEREAFTER. MID-LATITUDES ARE EXPECTED TO BE AT MINOR TO
MAJOR STORM LEVELS AND HIGH LATITUDES COULD HAVE PERIODS OF
SEVERE STORM LEVELS.
^^^^^^^^^^^^^^^^^^^^

This means an A-index over 100! That is black out time on HF.


IV.  PENTICTON 10.7 CM FLUX

OBSERVED           06 MAY 130
PREDICTED   07 MAY-09 MAY  130/125/125
90 DAY MEAN        06 MAY 106

V.  GEOMAGNETIC A INDICES

OBSERVED AFR/AP 05 MAY  023/036
ESTIMATED AFR/AP 06 MAY  007/010
PREDICTED AFR/AP 07 MAY-09 MAY  010/020-045/050-020/025


Date: Thu, 7 May 1998 01:48:32 -0600 (MDT)
From: Paul Harden <pharden@aoc.nrao.edu>
To: "Low Power Amateur Radio Discussion" [QRP-L]
Subject: Correction to May 5 Solar Report

First, thanks to everyone who has emailed me about the solar reports. I'm glad you are enjoying them.

It is my personal experience that most QRPer are well educated people and have strong interests in other areas of science besides radio. And my explanation yesterday proved that, as several sharp QRPers caught a fairly major mistake.

I inadvertently referred to "heavy electrons" when I meant to say "heavy particles." Electrons have a very constant mass, and heavy electrons would be some spooky, shady part of science, beyond the scope of this group! (We're talking Area 51 stuff).

Electrons travel through gravitational and magnetic fields fairy easily. But particles, being heavier, are bound by the gravitational and magnetic fields imposed on them. Like throwing a handful of flour into the air, they will scatter about but eventually fall to the ground as their mass is heavy enough to be pulled by gravity.

And this was an enigma to scientists for years. How do these heavy particles escape the sun's gravitational and magnetic fields to eventually strike the earth? Why aren't they simply pulled back towards the sun? We now know particles escape the sun in two major ways: through a CME (coronal mass ejection) and coronal holes.

A CME, usually the result of a flare, produces it's own magnetic field surrounding the solar disturbance, which punches a "hole" through the sun's magnetic field. These particles rise with the expanding magnetic field of the DISTURBANCE until beyond the influence of the SUN's magnetic field, usually several solar radii. Then they are propelled outward by the solar wind. So a point is reached where the OUTGOING solar wind exceeds the force of the INGOING magnetic and gravitational fields.

Coronal holes are still kind of mysterious. We had one for several days last week. It is a major "crack" in the solar surface that emits copious amounts of mass. This seems to also create it's own magnetic fields that fingers their way through the suns magnetic field. Coronal holes will often cause geomagnetic storming, even though no flare activity is occurring (like last week before the X-class flare on Thursday occurred). This mass usually escapes the sun in narrow fingers called coronal streamers. Incidentally, if you've seen photos of total solar eclipses, you will often see fingers of light poking outward from the sun. These are coronal streamers, and in fact, were discovered as a result of the total eclipse in 1970 centered over Virginia Beach, VA.

So sorry about the typo, but it did spawn the opportunity to explain the difference between electrons and the heavier particles.

I am receiving numerous emails requesting permission to reprint this solar information in local ham club newsletters to using them as handouts for high school physics classes. I am flattered at this kind of unexpected response. Everything I post to QRP-L I do to share ... so YES, you are free to use these posts for these purposes. On the solar stuff, feel free to use it (hopefully for non-commercial use) without any further need to obtain my permission. But I *do* appreciate you asking. A short credit line would be appreciated.

72, Paul NA5N
National Radio Astronomy Observatory
Socorro, New Mexico
Home of the VLA and VLBA radio telescopes.


Even More Stuff to Know and Tell

WHAT!! Still with us? Want more? Still not ready to scream! OK, here you go:


About the Ionosphere [HAARP]


A Beginner's Guide to the Earth's Magnetosphere [AGU]


The Magnetosphere [NASA]

Maile

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08/99