AstroAlert: Significant Major X-Class Solar Flare Alert - 28

[Ulrich Rieth]

A s t r o A l e r t

Sun-Earth Alert

Solar Terrestrial Dispatch

http://www.spacew.com

29 December 2001

SIGNIFICANT MAJOR X-CLASS SOLAR FLARE ALERT - 28 DEC

Images and movies available at:

http://www.spacew.com/astroalert.html

SIGNIFICANT MAJOR X-CLASS SOLAR FLARE ALERT - 28 DEC

Amateur and professional solar astronomers are waiting with anticipation
for the appearance of an active and presumed complex sunspot region to rotate
into view around the southeast limb of the Sun following the eruption of one
of the most energetic x-ray solar flares of this solar cycle on 28 December.

Even though the solar flare is thought to have originated from a sunspot
complex that was still about 2 days away from rotating into view around the
southeastern limb of the Sun, the x-rays from the solar explosion were strong
enough to attain a class X3.4 rating, briefly surpassing the entire x-ray
output of the Sun by a factor of about 100.

This event was also associated with one of the highest velocity coronal
mass ejections, as inferred by plane-of-sky velocity measurements using the
Solar and Heliospheric Observatory (SOHO) spacecraft and data from its LASCO
(Large Angle and Spectrometric Coronagraph Experiment) cameras. The estimated
plane-of-sky velocity of the ensuing coronal mass ejection was 2,170
kilometers per second (7.8 million kilometers per hour or almost 4.9 million
miles per hour). Such high velocity disturbances are fairly rare. It is,
perhaps, a good thing the trajectory of this particular disturbance was
directed well to the east of the Earth. But even so, model runs of this
disturbance by space weather forecasters suggest the Earth might observe a
weak impact from this disturbance on 31 December or 01 January. Had such a
disturbance been directed toward the Earth, a major to severe geomagnetic and
auroral storm may have developed with adverse affects felt on most orbiting
spacecraft. Fortunately, any effects we observe from this particular event
should not have any significant consequences due to its radial trajectory
being far from the Earth.

Solar x-ray flares can be categorized into varying levels of severity by
comparing the integrated x-ray energy output of the event. Most major solar
flares are associated with integrated x-ray flux values in the neighborhood
of 0.05 to 0.2 Joules. Strong x-ray flares are sometimes associated with
integrated x-ray flux values of around 0.5 Joules. The major X-class flare of
28 December was associated with an integrated x-ray flux in excess of 1.4
Joules. But even this pales in comparison to the integrated x-ray flux values
of some major solar flares observed during the last solar cycle. During the
last solar cycle, integrated x-ray fluxes of greater than 4 were observed
with a few particularly intense solar flare events. Whether this unseen
sunspot complex is capable of producing such intense x-ray flares remains to
be seen.

Observers are encouraged to watch the Sun closely over the next two
weeks for possible major outbursts of activity. Whether this active region
will remain capable of producing additional significant energetic events
through the next two week period will remain an open question until the group
rotates into full view over the coming days. Such energetic flares sometimes
end up resulting in the accelerated death of a complex sunspot group. In
other sunspot groups, energetic flares mark the onset of increasing magnetic
complexity and continue to produce energetic events for some time. Only
time will tell whether the sunspot complex that produced the major flare of
28 December will remain capable of producing energetic activity as it crosses
the visible disc of the Sun over the next two weeks.

Anyone interested in watching these events in real-time may do so at:
http://www.spacew.com/sunnow , where images of the Sun are provided by a host
of professional solar observatories world-wide in near real-time. Discussions
of this and future activity can be found at:
http://www.spacew.com/aurora/forum.html

** End of the AstroAlert Bulletin **
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