September 23-26 1998
Sun Signatures of the Event
September 23-26, 1998 EVENT SUMMARY
September 23, 07:00 UT M6.9 SOLAR FLARE
WIND/WAVES Data (from Mike Reiner)
Between about 06:00 on Sept 22 and 07:00 on Sept 23, a very intense type III storm was in progress. This is believed to be associated with closed or semi-closed loop structures -- we've seen many of these in the past. At the time of the M6.9 flare, we detected an extremely intense series of type III bursts AND the type III storm that had been raging abruptly disappeared as if the closed loop was blown away by the blast. After 07:00, we detected several drifting tones and bands of type II-like character. The most clearly defined of these began (i.e. became visible above the background) at about 2 MHz at about 07:25. This emission was observed from that time until about 12:00 as a very smooth band of emission drifting from 2 MHz down to 0.2 MHz. At 07:20 or thereabouts, there were also a couple of narrowband tones observed intermittently at frequencies in the 2-6 MHz range. Then at about 08:40, there were a couple of intense type III bursts followed by extremely intense, chaotic and broadband emissions in the 0.4 to 2 MHz band, whose center frequency drifts downward. We believe that this is very intense interplanetary type II emission because the 1/f plot indicates that it extrapolates back to an origin at ~7 UT. We may in fact be seeing an intense fundamental and weak harmonic.
For the smooth emission (07:25-12:00) - If this is emission at the fundamental, then the velocity is about 1000 km/sec, which would put arrival at Earth after 00:00 on Sept 25.
For the intense chaotic type II emission after 08:20, one would get a velocity of 400-500 km/sec for fundamental or 800-1000 km/s for harmonic, which would put the shock at Earth at either between 1 - 11 UT on Sept. 25 (harmonic) or between 18 UT on Sept. 26 and 15 UT on Sept. 27 (fundamental).
September 24, 23:19 UT (SHOCK at 250 RE from Earth)
September 25, 1 UT to 23 UT, Almost one full day of IMF South
September 25, 1 to 23 UT, Severe Geomagnetic Disturbances - Dst reached -222 nT at 7 UT.
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Last Updated: 09/03/98