A summary of the SXT images for the Nov. 3-4, 1993 geomagnetic storm.

General background:

There is a large trans-equitorial coronal hole extending from the northern into the southern hemisphere, which is east of disk center during the period of interest. On November 1, 1993, its western edge is between E5-15, the eastern edge is roughly E45, and it extends to S15 at the SW corner, S0 at the SE corner. Along the southern edge of the hole there are two active regions, one at S16E30 (unnumbered) and the other at S9E58 (AR7613). There is a set of loops connecting the two ARs.

As the two ARs come onto the disk the second one in particular is expanding,but there is nearly continuous activity from the whole complex. From late on October 31, there is a small region on the NW side of the AR7613 that seems to be involved in much of the activity and may well be an emerging flux region (EFR). This may serve as a trigger for several expansions and/or eruptive events. It seems to be involved in the increasing connections between the two ARs.

During the three days from October 30 through November 1 there were two mid C class flares, two small flares that rose just to the C level, and numerous small events. The first of the flares took place in the leading AR starting at about 11:00UT on October 31, and was the shorter, but also the more intense of the two. The second flare took place in AR7613 and started at about 20:40UT on November 1. These were both LDE flares that formed post-flare loop systems, though the second event which lasted over 12 hours was a better example of this class of flares.

In the SXT images we can see eruptive motions connected with both of these flares. There was also a possible eruptive episode from 12:00-14:00 on October 30, during which loops to the north of AR7613 can be seen to expand outwards.

The CME seen in the HAO Mauna Loa data at 19:00UT on Oct. 31 does not correspond obviously with any of the major active region activity. There were however, signs of field expansion on the southern side of AR7613 following the CME.

Summary:

It is clear that there was a good deal of activity in the region centered on AR7613 around the southern end of the coronal hole. There is evidence for two, possibly three, eruptive events between 11:00UT Oct. 31 and 20:00UT Nov. 1. These could all have reached Earth by the 17:00UT Nov. 3 sudden commencement without requiring extraodinary high velocities. The implied velocities would have been on the high side, but this may be explained in part by interaction with a 700-800 km/sec high speed wind coming from the nearby coronal hole.

It is most probable that the events that occurred at Earth on Nov. 3 and 4 were the result of more than a single event at the Sun. At the least the interaction of a CME with the high speed stream.

TRANSIT TIMES: Sun to Earth

1 day transit = 1740 km/sec ==>
2 day transit =  870 km/sec ==> Nov  1 17:00
3 day transit =  580 km/sec ==> Oct 31 17:00
4 day transit =  435 km/sec ==> Oct 30 17:00

Detailed event list:

Oct. 29,

• 18:00-20:00: Apparent flaring in both active regions, with possible loop expansions over the limb to the north of the trailing AR. Cusped, post-flare like loops to the south of the leading AR.

Oct. 30,

• 00:16: Compact flaring in the trailing AR.

Oct. 30,

• 00:00: Large faint event to the west of the lead AR. 1st AR. Possible changes between 20:13 and 23:07 on the 29th.
• 10:30: Compact flaring in the trailing AR.
• 12:00 - 14:00: Changes and expansion in the loops north of the trailing AR.

Oct. 31,

• 00:50; Compact flaring and larger newly bright loops in the trailing AR.
• 03:50; Flaring in small loops on the NW edge of the trailing AR. Brighting of loops to the NE as well.

Oct. 31,

• 10:59: Eruptive event in the lead AR,
• 11:56: flare peaks in the AR, sometime after 11:07.
• 13:33: Saturation spike gone. Arcade loops visible.

Oct. 31,

• 19:00-20:00: Mauna Loa CME off the east limb. It seems to center on the equator, +/- 20 degrees. The later image shows inhancements from N45-S50, skewed somewhat to the south. Between 19:55 and 20:15 UT the front seems to expand from ~2 Rs to ~2.5 Rs. This is about 290 km/s, not so fast.. Nothing obvious seen in SXT leading upto this.
• 20:30 - 22:00: Expansion and brightening of loops on the south side of the trailing AR. These might well be realted to the CME
• 23:16: Large remaining cusped loop over southern part of the AR.

Nov. 1,

• 01:10: Rearrangement of loops at NW edge of trailing AR, both compact and large scale, connections being made to leading AR.

Nov. 1,

• 06:20: Flaring in the trailing AR, from the small region on the NW side.
• 07:40: Large bright new loops on the NW side of the trailing AR.
• 11:16 - 11:26: Another small flaring, on the west side of the trailing AR.
• 12:38: Flaring in southern part of the trailing AR.

Nov. 1,

• 14:00: Changes in the following AR, south side, possible cusps. Expansion to 15:30.

Nov. 1,

• 20:40 - Nov. 2, 00:00: Large LDE flare in the following AR. Significant changes in the loops connecting to the leading AR.

Associated type IV radio burst (M. Dryer). 2000 km shock into 500 km solar wind according to STOA fits.

[Nov. 3, interesting signatures at Earth].

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