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
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.