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A solar filament collapsed on Tuesday, August 14th, and hurled a full-halo coronal mass ejection (CME) into space. NOAA forecasters estimate a 5% to 10% chance of strong geomagnetic activity at middle latitudes when the expanding CME strikes Earth's magnetosphere late Thursday or Friday.

Space Weather

-- spider (, August 15, 2001


-- spider (, August 16, 2001.

The flux of high-energy protons around our planet soared to 1000 times normal at ~0300 UT on August 16th. The ongoing S2-class solar radiation storm is unusual because it was not triggered by a major flare on the Earth-facing side of the Sun. Instead, it appears to be the result of a backside explosion detected by SOHO coronagraphs on August 15th.

Space Weather

-- spider (, August 16, 2001.

So whatn I want to know is -will this affect telecommunications? Will we lose television, radio, satellite communication?

-- John Littmann (, August 16, 2001.

Well, it's possible. Several such events last year did briefly disrupt radio communications, see the nice chart at It is possible for solar events to lead to power spikes and even blackouts in electricity grids. Reference the famous Quebec blackout, affecting millions of people, during the last solar cycle. And occasional satellite failures, sometimes directly affecting services like nationwide pagers, have been chalked up to solar events.

But it's not too likely you yourself will notice anything untoward from this particular event. Truth is, we most often sail through them (so to speak) without major mishap. See the left side of for some explanations and for estimates of the magnitude of solar events in the next 48 hours.

The folks most likely to need to worry about these events include technicians managing satellites; people using radio communications (especially with/from aircraft) at "high latitudes" i.e. near the earth's poles; and people in spacecraft (i.e. the international space station) or flying in planes at "high latitudes" (because with less atmosphere to protect them than we have at ground level, radiation doses go up).

The nice thing: an increased chance of seeing aurora at lower mid- latitudes (i.e. over the continental U.S., say around 40 degrees, i.e. my own latitude here in Pennsylvania...but it was cloudy last night, wouldn't you know it...)

-- Andre Weltman (, August 17, 2001.

RADIATION STORM: The flux of high-energy protons around our planet soared to 1000 times normal at ~0300 UT on August 16th. The ongoing S2-class solar radiation storm is unusual because it was not triggered by a major flare on the Earth-facing side of the Sun. Instead, it appears to be the result of a backside explosion detected by SOHO coronagraphs on August 15th.

-- spider (, August 17, 2001.

Note last few paragraphs as to effects:


Sender: Subject: AstroAlert: The Intriguing Energetic Solar Event of 16 August To: Date: Fri, 17 Aug 2001 00:12:26 -0600 (MDT)

A s t r o A l e r t

Sun-Earth Alert

Solar Terrestrial Dispatch

16 August 2001


Shortly after 00:30 UTC on 16 August (8:30 pm EDT on 15 August), a remarkably energetic and unusual solar event occurred that is worthy of an AstroAlert notice.

At around 00:30 UTC, proton sensors onboard spacecraft began observing an unusually energetic increase in the density of high energy protons. Usually, such strong bursts of radiation are produced by strong solar flares. But no obvious regions of activity capable of producing such strong bursts of radiation were visible anywhere on the visible Sun.

At 23:30 UTC on 15 August (7:30 pm EDT on 15 August), the SOHO spacecrafts LASCO instrument began imaging a rapid and bright full halo coronal mass ejection (named a halo CME because of the ring of light that the ejected mass forms around the Sun as it expands outward). Full halo CMEs are the result of mass being ejected from the Sun either toward or directly away from the Earth and are of high interest because of their potential Earthward trajectory.

It was immediately reasoned that the energetic proton burst was most likely associated with the bright and fast moving coronal mass ejection. This particular CME was determined by SOHO science members to be travelling outward along the plane of the sky at a speed as high as approximately 1,200 kilometers per second (4.3 million kilometers per hour or about 2.7 million miles per hour). Average velocities for CMEs are around 400 to 600 km/sec, so this disturbance was also somewhat unusual for its high outward velocity.

Part of the problem was in identifying the source of this activity. It did not occur anywhere on the visible side of the Sun that we see from the Earth, or spacecraft and ground-based telescopic instruments would have observed it. Even the Japanese Yohkoh x-ray imaging spacecraft (which takes regular images of the Sun in x-rays) did not appear to observe any clearly obvious signs of x-ray brightenings on the solar limbs or slightly behind the Sun. It therefore must have originated from somewhere fairly far behind the Sun where the high-altitude x-ray signatures of activity would be occulted by the Sun itself.

Evidence supporting this backside scenario came in the form of a sequence of images taken by the SOHO spacecraft at around 23:48 UTC. The EIT (extreme ultraviolet imaging telescope) onboard the SOHO spacecraft began to observe an interesting brightening all around the limb of the Sun. Scientists interpreted this limb brightening at extreme ultraviolet wavelengths as a coronal wave that propagated from the site of the solar explosion on the far side of the Sun to the limbs of the Sun that we can see from the Earth. Coronal waves are fairly common with coronal mass ejection disturbances. But coronal waves that travel such large distances are more rare.

Additional evidence became available through the science of helioseismology where vibrations on the solar surface are used to determine centers of sunspot activity on the far side of the Sun (much like seismologists on the Earth can determine the location of an earthquake from distant locations by measuring the vibrations they produce through the Earth). Scientists associated with the SOHO spacecraft resolved an area of increased activity in the southern solar hemisphere and on the opposite side of the Sun. This area coincides nicely with the predicted location of a potentially volatile sunspot group that was in the process of maturing when it rotated behind the western limb of the Sun and out of view late on 08 August.

Scientists and space weather forecasters therefore concluded that this energetic proton burst and the associated strong coronal mass ejection may have been produced by a strong solar flare and coronal mass ejection on the far side of the Sun within the sunspot group known as Region 9557.

Although this was a very interesting and exciting event for solar scientists and space weather forecasters, what was perhaps the most fascinating and puzzling aspect was the strength of the proton event and the rapidity with which it reached the Earth.

Most solar flares that produce strong proton bursts take time to reach the Earth. Protons are charged particles that can be accelerated to high velocities. Higher energy protons travel faster than lower energy protons. This particular event was associated with exceptionally high velocity protons travelling at near relativistic velocities (near the speed of light). Protons having energies greater than 100 million electron volts (MeV) were detected in abundance during this event. The near Earth space environment typically has fairly few protons that are energized to 100 MeV. But during this event, protons with energies greater than 100 MeV increased in density near the Earth to about 300 times normal background levels. It was categorized as a major high energy proton event.

The problem (and puzzle) with this activity was that the source of the proton enhancement was probably near the opposite side of the Sun. It is very rare for protons to reach the Earth from so far behind the Sun and even rarer for protons to reach the Earth so rapidly after an event occurs on the far side of the Sun. In fact, such a prompt and intense proton event has apparently never been observed from such a distant location near the other side of the Sun.

Most energetic proton solar flares that have occurred behind the Sun have resulted in mild enhancements of protons many hours after the event occured with relatively few high energy protons at > 100 MeV. It usually takes hours for the accelerated protons to diffuse through the solar atmosphere to the point where the Sun's magnetic field can carry them to the Earth (charged particles like protons move most easily along magnetic field lines - they do not move easily across magnetic field lines).

So one of the big questions that has been raised is: how did this particular solar event produce such an intense and rapid response at the Earth? There will undoubtably be many scientific papers over the ensuing years that attempt to address this question.

This energetic proton event produced serious degradations in space-based images of the Sun and has affected spacecraft star- tracking cameras and other imaging instruments on spacecraft by introducing streaks of light (caused by high-energy protons impacting the imaging electronics) that can confuse the instruments. Such energetic proton events can also produce permanant degradation in the electrical generating efficiency of spacecraft solar array panels. Other spacecraft anomalies can (and do) accompany such strong proton events.

Fortunately (or unfortunately, if you are an avid aurora hunter), the coronal mass ejection disturbance associated with this event is directed outward and away from the Earth. We will therefore not see the direct effects of this disturbance, although we will continue to suffer the effects of the high energy proton event in space for several more days to come. It should be noted that this event is harmless to life on Earth. The Earth's atmosphere (ionosphere) shields us from the effects of the enhanced proton related space radiation. And although the astronauts on the international Space Station will observe slightly higher radiation levels during this event, the radiation hazard is still considered low.

It will be interesting to monitor solar conditions over the next 4 to 8 days. Sunspot Region 9557 may rotate back into view around the east limb of the Sun at that time. Whether it rotates into view as a potent sunspot group capable of producing significant energetic solar flares is a question that many will be asking. Activity from that region fo the Sun will be closely monitored over the next 7 to 10 days, primarily in the form of coronal mass ejection intensity and helioseismic signatures.

Solar observers may want to pay special attention to the southeast limb of the Sun as Region 9557 begins to approach it over the next week.

** End of AstroAlert **


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-- Andre Weltman (, August 20, 2001.

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