Solar Terrestrial Activity Report

Last update issued on October 21, 2003 at 03:30 UTC. Minor update posted at 10:35 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 15, 2003)]

Recent activity

The geomagnetic field was unsettled to minor storm on October 20. Solar wind speed ranged between 494 and 700 km/sec under the influence of a high speed stream from coronal hole CH63.

Solar flux measured at 20h UTC on 2.8 GHz was 135.1. The planetary A index was 30 (STAR Ap - based on the mean of three hour interval ap indices: 32.3).
Three hour interval K indices: 34554445 (planetary), 34434445 (Boulder).

The background x-ray flux is at the class C1 level.

At midnight there were 4 spotted regions on the visible disk. Solar flare activity was moderate. A total of 12 C and 1 M class flares was recorded during the day.

Region 10482 decayed slowly and quietly.
Region 10483 reemerged quickly early in the day and soon developed a magnetic delta structure. This delta disintegrated late in the day but the region could still produce C flares.
Region 10484 continued to develop rapidly and is now in the top 5 list of the largest spotted regions during solar cycle 23. A strong magnetic delta structure is embedded in the main penumbra. A delta in the southern penumbra has become much stronger and could easily become the origin of major flares. Major flares are likely and could occur anytime during the next few days. There's a slight possibility of an X10+ proton flare. Multiple earth directed solar storms (CMEs) are likely to be generated by this region as long as the delta structures persists. Flares: C5.1 at 00:24, C4.9 at 01:08, C1.8 at 05:41, M1.9/2N at 07:22, C1.1 at 13:19, C1.9 at 14:26, C3.3 at 14:49, C3.2 at 15:55, C1.6 at 17:03, C2.4 at 18:24, C5.9 at 20:02, C4.5 at 20:46 and C6.1 at 22:02 UTC.

Spotted regions not numbered by NOAA/SEC:
[S281] A new region emerged in the southeast quadrant on October 20. Location at midnight: S06E55.

Comment added at 10:35 UTC on October 21: Development in the southeastern part of region 10484 has caused another magnetic delta structure to form. This is also the part of the region where penumbral area has increased the most since midnight. The two main penumbrae could be merging, at least the penumbraless area between them has decreased, especially in the eastern section.
Region 10483 has redeveloped a magnetic delta structure, the main penumbra has both negative and positive polarity spots.
The background x-ray flux has increased to the C2 level.
A large CME was observed off of the southeast limb beginning at 03:54 UTC in LASCO C2 images. Its source is a region at or just behind the southeast limb.
Solar wind speed, which had increased yesterday as the high speed stream from the well defined eastern part of coronal hole CH63 became the dominant solar wind influence, has been decreasing slowly all day.

Coronal mass ejections (CMEs)

October 20: No potentially geoeffective CMEs observed.

October 19: A full halo CME was observed in LASCO C3 images after the X1 flare in region 10484. Although most of the ejected material was observed off of the northeast limb and the CME was faint in the southwest, this CME could cause a significant geomagnetic disturbance on October 22.

October 18: A halo CME was observed in LASCO C3 images beginning at 16:18 UTC and was likely associated with an event near the east limb. It is not yet certain if the event was associated with activity in region 10484 or another region 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 trans equatorial hole (CH63) was in a geoeffective position on October 12-19.

Processed SOHO/EIT 284 image at 01:06 UTC on October 21. The darkest areas on the solar disk are likely coronal holes.

Forecast

The geomagnetic field is expected to be unsettled to minor storm on October 21 and early on October 22 due to a high speed stream from coronal hole CH63. The CME associated with the X1 flare on October 19 will likely cause active to major geomagnetic storm conditions on October 22.

Long distance low frequency (below 2 MHz) propagation along east-west paths over high and upper middle latitudes is useless. Propagation along north-south paths is poor. [Trans Atlantic propagation conditions are currently monitored every night on 1470 kHz. Dominant station tonight: Radio Cristal del Uruguay. An unidentified Argentine station from the Buenos Aires area was heard as well].

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.