Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!cis.ohio-state.edu!ucbvax!HG.ULeth.CA!oler From: oler@HG.ULeth.CA (oler, CARY OLER) Newsgroups: sci.space Subject: SIGNIFICANT MAJOR SOLAR FLARE ALERT - IMPACT EXPECTED Message-ID: <910615121640.27a001b2@HG.ULeth.CA> Date: 15 Jun 91 18:16:40 GMT Sender: daemon@ucbvax.BERKELEY.EDU Distribution: world Organization: The Internet Lines: 70 -- 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 **