Solar Terrestrial Activity Report

Last update issued on October 24, 2003 at 04:10 UTC. Minor update posted at 19:42 UTC.

[Solar and geomagnetic data - last month (updated daily)]
[Solar wind and electron fluence charts (updated daily)]
[Solar cycles 21-23 (last update October 4, 2003)]
[Solar cycles 1-20]
[Graphical comparison of cycles 21, 22 and 23 (last update October 4, 2003)]
[Graphical comparison of cycles 2, 10, 13, 17, 20 and 23 (last update October 4, 2003)]
[Historical solar and geomagnetic data charts 1954-2003 (last update October 15, 2003)]
[Archived reports (last update October 22, 2003)]

Recent activity

The geomagnetic field was quiet to unsettled on October 23. Solar wind speed ranged between 375 and 584 km/sec, generally decreasing all day. The interplanetary magnetic field was northwards all day.

Solar flux measured at 17h UTC on 2.8 GHz was 183.2 (the 20h UTC value was enhanced by an X1 flare). The planetary A index was 7 (STAR Ap - based on the mean of three hour interval ap indices: 8.5).
Three hour interval K indices: 32222222 (planetary), 31213332 (Boulder).

The background x-ray flux is at the class C4 level.

At midnight there were 5 spotted regions on the visible disk. Solar flare activity was high. A total of 2 C, 5 M and 2 X class events was recorded during the day.

Region 10484 decayed slightly in the northeast and in the southwest sections. Otherwise the region was mostly unchanged and has several magnetic delta structures. Major flares are likely. Flares: M2.4 at 02:41, M3.2/1N at 07:08 and M2.7 at 10:53 UTC.
Region 10485 decayed slowly and quietly, the region could become spotless today.
Region 10486 rotated fully into view revealing a complex region with multiple magnetic delta structures. The region is likely to continue producing major flares. An X10+ proton flare may be possible. Flares: major X5.4/1B at 08:35,  M1.0 at 16:07, major X1.1/1N at 20:04 and M1.3 at 22:28 UTC. This region was the source of a long duration M7.8 event peaking at 02:53 UTC on October 24 as well.

Spotted regions not numbered by NOAA/SEC:
[S284] A new region emerged in the northwest quadrant on October 23. Location at midnight: N07W47.
[S285] This region emerged in the northwest quadrant on October 23. Location at midnight: N04W22.

Comment added at 19:42 UTC on October 24: A fairly strong solar wind shock was observed at SOHO at 14:47 UTC with a sudden increase in solar wind speed from 450 to 620 km/sec. The geomagnetic field has been at minor to severe storm levels since about 15:30 UTC.

Coronal mass ejections (CMEs)

October 23: The X5 flare in region 10486 at 08:35 UTC was associated with a large and fast full halo CME. The CME was well defined in the east and faint in the west. While Earth will not receive an impact from the main part of the CME, a glancing shock is likely to arrive at Earth on October 25. The X1 flare in region 10486 at 20:04 UTC produced another CME, not quite as large as the one observed earlier in the day. Still, there is chance of a glancing blow from this CME as well.

October 22: A CME was observed off of the southeast limb following a long duration M3 event in region 10486. This CME is not likely to become geoeffective. A partial halo CME was observed in LASCO C3 images beginning at 10:20 UTC. Ejected material was first observed over the north pole and the northwest limb then below the south pole and the southwest limb at 10:42 UTC. By 12:42 UTC the CME had expanded to cover the entire west limb and high latitude parts of the northeast and southeast limbs. The distribution of the ejected material and the lack of frontside activity in the northwest quadrant suggests a source about 6 days behind the northwest limb. Other observers point to possible frontside sources in an erupting filament (mainly in the southeast quadrant) and an erupting loop system in the northern hemisphere. The major M9.9 flare in region 10486 at 20:07 was associated with a fast full halo CME. Most of the ejected material was observed over the southeast limb, the CME was faint over the west limb.

October 21: A large full halo CME was observed beginning at 03:54 UTC at the southeast limb. The source of this CME is a region one or two days behind the southeast limb. Further CMEs were observed late in the day from two sources at and just behind the southeast limb.

Coronal holes

Coronal hole history (since late October 2002)
Compare today's report with the situation one solar rotation ago: 28 days ago 27 days ago 26 days ago

A recurrent coronal hole in the northern hemisphere (CH64) could rotate into a geoeffective position on October 25-26. During the previous solar rotation this coronal hole did not cause a geomagnetic disturbance.

Processed SOHO/EIT 284 image at 01:06 UTC on October 24. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be quiet to unsettled early on October 24. One or two solar wind shocks will likely arrive during the day and cause unsettled to major storm conditions. Further shocks are likely on October 25 and unsettled to major storm is likely that day as well.

Long distance low frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is very poor. Propagation along north-south paths is poor. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant station tonight: Radio Vibración (Venezuela)].

Coronal holes (1)	Coronal mass ejections (2)	M and X class flares (3)

1) Effects from a coronal hole could reach Earth within the next 5 days.
2) Material from a CME is likely to impact Earth within 96 hours.
3) There is a possibility of either M or X class flares within the next 48 hours.

Green: 0-20% probability, Yellow: 20-60% probability, Red: 60-100% probability.

Active solar regions (Recent map)

Compare to the previous day's image.

Data for all numbered solar regions according to the Solar Region Summary provided by NOAA/SEC. Comments are my own, as is the STAR spot count (spots observed at or inside a few hours before midnight) and data for regions not numbered by SEC or where SEC has observed no spots.

Monthly solar cycle data

1) Running average based on the daily 20:00 UTC observed solar flux value at 2800 MHz.
2) Unofficial, accumulated value based on the Boulder (NOAA/SEC) sunspot number. The official international sunspot number is typically 30-50% less.

This report has been prepared by Jan Alvestad. It is based partly on my own observations and analysis, and partly on data from sources noted in solar links. All time references are to the UTC day. Comments and suggestions are always welcome.