oler@HG.ULeth.CA (oler, CARY OLER) (06/16/91)
-- MAJOR SOLAR FLARE ALERT --
JUNE 15, 1991
Flare Event Summary
Potential Impact Assessment
--------
MAJOR ENERGETIC EVENT SUMMARY
Region 6659 has managed to spawn another Great Flare, rated as a class
X12/3B tenflare from a location of N33W69. The energy released by this event
was enormous. Protons were ejected with high-energies. The cosmic ray
neutron monitors registered a Ground Level Event (GLE) of +18% at 09:40 UT.
The neutron monitors are back near background levels. Todays major flare was
very long in duration. It began at 08:10 UT, peaked at 08:18 UT and ended at
14:02 UT on 15 June (almost six hours in duration!). There were major
(importance 3) Types II and IV sweeps with this event. The integrated x-ray
flux was high, at 2.85. There were fairly strong radio bursts across the
spectrum. The 10 cm burst was 14,000 sfu while the 245 MHz burst was 6,400
sfu.
Near relativistic protons were observed with this event, which has
produced another strong PCA event. Protons at greater than 100 MeV peaked at
77 pfu at 10:10 UT on 15 June. A brief SST Radiation Alert for radiation
greater than or equal to 10 millirems was issued at 10:00 UT on 15 June.
Conditions have since relaxed and this radiation hazard alert for high
altitude aircraft has ended. The 10 MeV protons climbed quickly to a
preliminary peak of 1700 pfu at 17:05 UT on 15 June. This peak is
preliminary, since protons at greater than 10 MeV are currently running at
levels near 900 pfu. Sporadic excursions above this peak may still occur.
Polar radio signal paths have again been blacked out from this last
proton blast from Region 6659. Polar Cap Absorption (PCA) levels peaked at
15:55 UT with a preliminary value of about 6.3 dB. However, this peak is
preliminary and excursions beyond this point may still be possible. PCA is
currently running ~ 5 dB.
The 10 cm radio burst from this flare remained 100% above background
levels for 123 minutes. The 10 cm burst began at 08:13 UT on 15 June.
POTENTIAL TERRESTRIAL IMPACT ASSESSMENT
Despite the relatively poor position of this flare, we are considering a
fairly strong possibility for a minor to major geomagnetic storm beginning
sometime on 17 June. A-indices of greater than 50 may be possible. This
flare has released sufficient energy to be a threat, even at its present
position. We are still performing analysis and will release an official
forecast within the next few hours. If storm conditions are expected, this
forecast will be released with a Potential Geomagnetic Storm Warning.
A major HF blackout has been reported by the areas which were sunlit
during this event. X-rays have now dropped below M-class levels and are
continuing to slowly decay back toward background levels.
Major flaring will continue to be possible from this Region, although
another X-class event likely will not be observed before this region crosses
the west limb. It is obviously still a potent region.
Watch for another bulletin or Warning stating the expected forcast for
this event later this UT day.
** End of Alert **